- Email: [email protected]
Effect of silver co-doping on enhancement of the Sm3+ luminescence in lithium tetraborate glass
Journal of Luminescence 213 (2019) 290–296
Contents lists available at ScienceDirect
Journal of Luminescence journal homepage: www.elsevier.com/locate/jlumin
Effect of silver co-doping on enhancement of the Sm3+ luminescence in lithium tetraborate glass
T
I.I. Kindrata, B.V. Padlyaka,b,∗, B. Kuklińskic, A. Drzewieckia, V.T. Adamivb a
University of Zielona Góra, Institute of Physics, 4a Szafrana Str., 65-516, Zielona Góra, Poland Vlokh Institute of Physical Optics, Department of Optical Materials, 23 Dragomanov Str., 79-005, Lviv, Ukraine c University of Gdańsk, Institute of Experimental Physics, 57 Wita Stwosza Str., 80-308, Gdańsk, Poland b
A R T I C LE I N FO
A B S T R A C T
Keywords: Borate glasses Sm3+ ions Luminescence spectra Ag+ ions Silver nanoparticles Quantum yield
Luminescent properties of the Sm3+-doped and Sm3+-Ag co-doped glasses with Li2B4O7 (or Li2O–2B2O3) basic composition are investigated and analysed. Spectroscopic properties of the obtained Li2B4O7:Sm and Li2B4O7:Sm, Ag glasses were studied using measurements of optical absorption, electron paramagnetic resonance (EPR), photoluminescence (excitation, emission, decay kinetics), and quantum yield (QY) via an absolute method. Optical absorption spectra exhibit absorption bands related with transitions from the ground 6H5/2 state of Sm3+ ions to several excited states. Photoluminescence spectra of the Sm3+-doped glasses reveal emission bands, which correspond to the 4G5/2 → 6HJ (J = 5/2–13/2) transitions of Sm3+ ions. Luminescence excitation spectra and decay curves of the Sm3+ luminescence also have been analysed. The EPR study confirms presence of Ag species in the Sm3+-Ag co-doped samples. Photoluminescence emission and excitation spectra and luminescence decay kinetics of the Ag+ ions and small non-plasmonic molecule-like silver (ML-Ag) nanoclusters are observed and discussed. Enhancement of Sm3+ luminescence in the Li2B4O7:Sm, Ag glass has been observed. Measurements confirm the increasing of external QY of the Sm3+ luminescence in 1.43 times in the Ag co-doped glass. Such enhancement of the luminescence is attributed to the excitation energy transfer from Ag+ ions and ML-Ag nanoclusters to the Sm3+ ions. The obtained high QY of the Sm3+ luminescence shows that Li2B4O7:Sm, Ag glasses belong to promising luminescent materials.
1. Introduction In the last decades, the studies of borate glasses represents significant practical interest, because these glasses reveal attractive optical and spectroscopic properties [1–6]. Practical interest to borate glasses, generally, is caused by two aspects. At first, glassy borate compounds are more promising materials than corresponding crystals thank to simple and inexpensive producing technology. At second, the network of borate glasses allows to incorporate considerably higher amount of the impurity lanthanide (Ln) ions in comparison with their crystalline analogies. At present time special interest represent borate glasses with Li2O–2B2O3 basic composition that is identical to the well-known lithium tetraborate (Li2B4O7) crystal [4–6]. Attractive luminescent properties of materials doped with lanthanide ions, including Sm3+ ions, initiated potentialities for their wide practical application e.g. in solid-state lighting, laser technique, energy transformers, sensors, displays, telecommunication devices, etc. [7,8]. The Sm3+ (4f5, 6H5/2) ions in oxide glasses reveal characteristic intense
∗
yellow, orange, and red emission bands, which are related to the 4G5/ 6 4 6 4 6 2 → H5/2, G5/2 → H7/2, and G5/2 → H9/2 emission transitions, respectively. Up to present time, the luminescent properties of different Sm3+-doped borate glasses were widely studied and reported in number papers, notably in Refs. [9–12]. The luminescent properties of the Sm2+ (4f6, 7F0) ions in oxide glasses were published only in few articles [13–15]. Luminescence of Sm2+ ions is characterised by broad emission in the red spectral region. Generally, the Sm2+ stable ions can be formed in glasses only during synthesis in strongly reduced atmospheres [14,15], whereas the Sm2+ ions created by X- or γ-radiation are unstable [13,14]. The Sm3+ ions reveal abovementioned efficient photoluminescence. However, cross-section of the Sm3+ absorption transitions, particularly in the ultraviolet (UV) region, is not very high due to the parity forbidden 4f – 4f transitions. Therefore, additional approaches are required in order to increase the light output of the Sm3+ luminescence. At present time, co-doping with silver is investigated as an attractive approach to improve the luminescence output of lanthanide ions.
Corresponding author.University of Zielona Góra, Institute of Physics, 4a Szafrana Str., 65-516, Zielona Góra, Poland. E-mail address: [email protected] (B.V. Padlyak).
https://doi.org/10.1016/j.jlumin.2019.05.045 Received 14 April 2019; Received in revised form 16 May 2019; Accepted 17 May 2019 Available online 20 May 2019 0022-2313/ © 2019 Elsevier B.V. All rights reserved.
Journal of Luminescence 213 (2019) 290–296
I.I. Kindrat, et al.
Enhanced luminescence of Eu3+ ions as a result of the local-field effect, caused by surface plasmon resonance (SPR) of the Ag nanoparticles was observed in the CaF2–B2O3 glass by Malta et al. [16]. Jiménez et al. [17] report enhanced Sm3+ photoluminescence in aluminophosphate glass co-doped with Ag due to the energy transfer from the Ag+ to Sm3+ centres. Transfer of excitation energy from non-plasmonic moleculelike gold and silver particles to the Ln3+ ions was noticed for the first time in soda-lime silicate glasses by Eichelbaum and Rademann [18]. Currently three different processes of the Ln3+ luminescence enhancement in the co-doped with Ln and Ag glasses had been proposed. Up to present time, enhancement of the Sm3+ luminescence related with SPR effect was reported in sodium borosilicate [19], heavy metal fluorotellurite [20], and sodium-zinc tellurite [21] glasses. It should be noted that a quenching effect of Sm3+ photoluminescence with the presence of metallic silver nanoparticles was reported in Refs. [22,23]. Transfer of the excitation energy from Ag+ to Sm3+ centres was stated in oxyfluoride [24] and fluorophosphate [25] glasses. At last, the excitation energy transfer from different silver species to Sm3+ ions have been observed in sodium-aluminosilicate glass [23]. The number of studies of borate glasses co-doped with Sm3+ and Ag is very limited at present time. Dyrba et al. [26] observe SPR-related absorption band of silver nanoparticles in lithium and sodium borate glasses. However, it was concluded that influence of plasmon resonance in these glasses is too small to enhance the fluorescence emission [26]. In previous year, scientists from Kyoto University report study of Sm3+doped aluminoborate glass containing Ag nanoparticles [27]. The intensity of visible Sm3+ photoluminescence near 600 nm was enhanced under excitation at 400 nm in 1.398 times [27]. The enhancement was ascribed to the SPR of Ag nanoparticles [27]. Luminescent properties of the Sm3+-doped borate glasses with different compositions (Li2B4O7, LiKB4O7, CaB4O7, and LiCaBO3) preliminary have been studied by us in Ref. [4]. Attractive results were obtained for the Sm3+-doped lithium tetraborate (Li2B4O7:Sm) glass that reveals highest quantum yield (QY) of luminescence among the investigated glasses [12]. Consequently, the main aim of this article is to investigate the effect of silver co-doping on the possibility to enhance of the Sm3+ luminescence in the lithium tetraborate glasses. This paper mainly is focused on the analysis of luminescence QY in the Li2B4O7 glasses, doped with Sm3+ and co-doped with Sm3+ and Ag as well as mechanisms related to the Sm3+ photoluminescence enhancing, caused by the Ag dopant.
Fig. 1. The XRD patterns of the Li2B4O7:Sm (a) and Li2B4O7:Sm, Ag (b) glasses.
polished to the approximate size of 10 mm × 7 mm × 2 mm. For electron paramagnetic resonance (EPR) investigation the obtained glass samples were cut to the approximate size of 5 mm × 3 mm × 2 mm. 2.2. Experimental equipment The XRD (X-ray diffraction) investigations were performed with usage commercial X-ray diffractometer (model DRON-3) controlled by computer. The XRD patterns of the Li2B4O7:Sm and Li2B4O7:Sm, Ag glasses are presented in Fig. 1. Obtained diffractograms show typical glassy-like pattern without any discrete sharp peaks that confirms disordered glass structure of the investigated Li2B4O7:Sm and Li2B4O7:Sm, Ag samples. Optical absorption spectra were registered with usage Shimadzu (model UV-2600) spectrophotometer. Emission and luminescence excitation spectra as well as decay curves were registered using Horiba Yvon (model FluoroMax–4) spectrofluorimeter. The luminescence spectra and kinetics were registered at room temperature with usage the same holder for solid bulk sample. Excitation and monitoring wavelengths for registered luminescence spectra are indicated in corresponding figures. The quantum yield of luminescence was registered by Hamamatsu Quantaurus-QY Absolute PL quantum yield spectrometer (model C11347). Paramagnetic centres have been registered with usage commercial X-band “Radiopan” (Poland) EPR spectrometer (model SE/X-2013) controlled by computer. The effective g-factor (geff) of observed EPR signals was calculated using the following relation:
2. Experimental details 2.1. Borate glasses synthesis and samples preparation The Li2B4O7 glasses doped with Sm3+ and co-doped with Sm3+ and Ag were produced using standard melt-quenching glass technology [28]. Initially, the mixture of the Li2CO3 and H3BO3, taken in the stoichiometric proportion, has been prepared. The Li2B4O7 powdered compound was synthesised in the air using the following multi-step heating reaction: 4H2 O↑
geff =
(2)
where h is the Planck constant, μB is the Bohr magneton, Br is the resonance magnetic field, and ν is the working frequency of EPR spectrometer.
2H2 O↑
Li2 CO3 + 4H3 BO3 →o Li2 CO3 + 4(α − НВО2) →o 170 C
hν μB Br
250 C
CO2 ↑
Li2 CO3 +2B2 O3 →o Li2 B4 O7 800 C
3. Results and discussion
(1)
3.1. The optical absorption spectra
Then, the Sm2O3 in amount of 1.0 mol.% (for obtaining of the Li2B4O7:Sm glass) or Sm2O3 in amount of 1.0 mol.% and AgNO3 in amount 2.0 mol.% (for obtaining of the Li2B4O7:Sm, Ag glass) were added to the as-synthesised Li2B4O7 powdered compound and thoroughly mixed. Obtained mixtures were heated and melted in a corundum ceramic crucible. Large samples of the Li2B4O7 glasses doped with Sm3+ and co-doped with Sm3+ and Ag of high chemical purity and optical quality were obtained by quick cooling of the corresponding melts. The bulk glass samples for optical measurements were cut and
Optical absorption spectra of the Li2B4O7 glasses doped with Sm3+ and co-doped with Sm3+ and Ag, registered in the 300–800 nm spectral range are presented in Fig. 2. Significant increasing of optical absorption below 340 nm is attributed to the fundamental absorption edge of the glass matrix. In registered absorption spectra have been observed several bands of weak intensity belonging to the Sm3+ ions (see inset in Fig. 2). The most intense absorption band that is peaked about 402 nm 291
Journal of Luminescence 213 (2019) 290–296
I.I. Kindrat, et al.
Fig. 3. The X-band EPR spectra of the Li2B4O7:Sm (a) and Li2B4O7:Sm, Ag (b) glasses, recorded at T = 295 K. Fig. 2. The optical absorption spectra of the Li2B4O7:Sm (a) and Li2B4O7:Sm, Ag (b) glasses, recorded at T = 295 K in the range of 300–800 nm.
inhomogeneously broadened signals of isolated Ag0 and Ag2+ centres as well as their paramagnetic nanoclusters and aggregates with unresolved HF and SHF structures.
corresponds to the 6H5/2 → 6P3/2 transition. Spectrum of optical absorption of the Li2B4O7:Sm, Ag glass reveals additional weak band in the 410–425 nm range (Fig. 2). The broadband absorption peaked near 418 nm is assigned to the SPR (surface plasmon resonance) of the Ag metallic nanoparticles, or most precisely – resonant oscillations of the conduction electrons in the Ag nanoparticles, stimulated by an incident light. It is worth noting that registered SPR band intensity in several dozen times is less than intensities of SPR bands with maxima located between 436 and 450 nm in sodium borosilicate glass [19], around 430 nm in lithium and sodium borate glasses [26], and about 425 nm in aluminoborate glass [27]. Hence, the amount of silver nanoparticles (Ag0) in the investigated Li2B4O7:Sm, Ag glass is relatively small.
3.3. Luminescence emission and excitation spectra of the Sm3+ ions In Fig. 4 are presented the Sm3+ emission spectra in the Li2B4O7 glasses doped with Sm3+ (1.0 mol.% of Sm2O3) and co-doped with Sm3+ (1.0 mol.% of Sm2O3) and Ag (2.0 mol.% of AgNO3). The Sm3+ emission intensity in the Li2B4O7:Sm, Ag glass increases in 1.5 times in comparison with Li2B4O7:Sm glass, but the form of emission bands are much the same. The Sm3+ emission spectra reveal three intense bands in the 550–670 nm region and two weak bands in the 670–820 nm range (Table 1). The observed bands refer to 4G5/2 → 6HJ (J = 5/2, 7/2, 9/2, 11/2, and 13/2) emission transitions of the Sm3+ centres, which are denoted in Fig. 4. Excitation spectra of the Sm3+-doped and Sm3+-Ag co-doped Li2B4O7 glasses, registered at T = 295 K by monitoring of luminescence intensity at λmon = 598 nm are given in Fig. 5. The Ag co-doping causes the raising of intensities of excitation bands in the Li2B4O7:Sm, Ag glass. Observed in the excitation spectra bands according to Refs. [34,35]
3.2. EPR spectroscopy of the Li2B4O7:Sm, Ag glass The impurity of samarium can reveals in oxide compounds as paramagnetic Sm3+ (4f5, 6H5/2) Kramers ions and Sm2+ (4f6, 7F0) nonKramers ions. The isolated Sm3+ ions in the Li2B4O7 glass show asymmetric broad EPR signal with geff ≅ 9.7 observed only at low temperatures (T ≤ 20 K) [4]. The silver dopant into the structure of oxide compounds can be incorporated as Ag2+ (4d9, 2D5/2), Ag+ (4d10, 1 S0), and Ag0 (4d105s1, 2S1/2) ions. The paramagnetic Ag2+ and Ag0 ions can be detected by EPR. Isolated Ag2+ ions in EPR spectra of the Li2B4O7:Ag crystals [29–31] show characteristic doublets, cause by hyperfine (HF) interactions of electron spin S = 1/2 with nuclear spin I = 1/2 of both 107Ag and 109Ag isotopes. Isolated Ag0 ions in Li2B4O7:Ag crystals reveal 16 lines as a result of HF interaction of electron spin with the 107Ag and 109Ag nuclei (I = 1/2) and superhyperfine (SHF) interaction with nuclei of 11B (I = 3/2) [29–31]. In Fig. 3 are presented the X-band EPR spectra of the Li2B4O7 glasses, doped with Sm3+ and co-doped with Sm3+ and Ag. In the Li2B4O7:Sm and Li2B4O7:Sm, Ag glasses has been registered the sharp EPR signal with the following parameters: geff = 4.296 ± 0.005 and peak-to-peak derivative linewidth ΔBpp = (7.7 ± 0.5) mT as well as geff = 4.297 ± 0.005 and ΔBpp = (7.8 ± 0.5) mT, respectively. Observed signal is typical for glass network and according to Refs. [4,32,33] is attributed to the non-controlled Fe3+ (3d5, 6S5/2) isolated ions, which are localised in the octahedral and/or tetrahedral sites with a strong rhombic distortion. Broad unresolved complex EPR signal with geff = 2.07 ± 0.01 and ΔBpp = (88 ± 5) mT that is observed only in the Li2B4O7:Sm, Ag glass (see Fig. 3) belongs to the superposition of
Fig. 4. The luminescence emission spectra of the Li2B4O7:Sm (a) and Li2B4O7:Sm, Ag (b) glasses containing 1.0 mol.% Sm2O3, registered under excitation with λexc = 402 nm (6H5/2 → 6P3/2 transition) at T = 295 K. 292
Journal of Luminescence 213 (2019) 290–296
I.I. Kindrat, et al.
Table 1 The peak position (λmax), full width at high maximum (FWHM) and luminescence branching ratio (β) of emission bands in the Sm3+-doped and Sm3+-Ag co-doped Li2B4O7 glasses. Transitions
G5/2 → 6H5/2 G5/2 → 6H7/2 4 G5/2 → 6H9/2 4 G5/2 → 6H11/2 4 G5/2 → 6H13/2 4 4
Li2B4O7:Sm
Li2B4O7:Sm,Ag
λmax (nm)
FWHM (cm−1)
β
λmax (nm)
FWHM (cm−1)
β
562 598 645 705 790
289 281 271 553 680
0.210 0.549 0.218 0.022 0.001
562 598 645 704 787
283 294 276 563 690
0.206 0.555 0.216 0.022 0.001
Fig. 6. The luminescence emission spectra of the Li2B4O7:Sm (a) glass as well as luminescence excitation (dashed curves) and emission (solid curves) spectra of the Li2B4O7:Sm, Ag (b) glass at T = 295 K. Wavelengths of excitation (λexc) and monitoring (λmon) are denoted in the Figure.
spectrum upon 352 nm excitation has been observed a broad band peaked at 440 nm [41]. Recently, the strong broad emission from 400 nm to 700 nm ascribed to silver aggregates or silver nanoclusters was observed in calcium borate [42], calcium fluoroborate [43], and multicomponent fluorophosphate [44,45] glasses. Generally, silver dopant in glass network gives positive influence for energy transfer effects, improving of colour coordinates, generation of white light or tuneable emission [42,44]. But, as it was mentioned above, the quenching of Sm3+ luminescence in glasses co-doped with Ag also can be observed [22,23]. Therefore, here it is worth noting the new interesting results [46] about possibility of spatial redistribution of silver species in phosphate glass induced by a femtosecond laser. The luminescence emission spectra of the Li2B4O7:Sm and Li2B4O7:Sm, Ag glasses registered upon excitation of 266 nm are given in Fig. 6. The Li2B4O7:Sm glass shows broadband intrinsic luminescence with a peak near 465 nm and the Sm3+ emission bands in the 550–720 nm spectral region. The intrinsic luminescence of un-doped borate glasses has been investigated in details by us in Ref. [47]. The broadband intrinsic luminescence peaked about 470–490 nm was observed in the Li2B4O7, LiKB4O7, CaB4O7, and LiCaBO3 glasses under excitation at 270 nm [47]. The intrinsic emission band peaked about 470–490 nm in the un-doped borate glasses is related to recombination of the UV-generated O− hole centres with electrons [47]. In the Li2B4O7:Sm, Ag glass, intense photoluminescence of silver dopant was observed in the range of 350–500 nm (see Fig. 6). Observed emission of Ag dopant consists of a strong band near 390 nm and a weaker band about 410–450 nm. The excitation spectrum reveals a broad band peaked near 266 nm. The luminescence emission spectrum of the Li2B4O7:Sm, Ag glass registered under 352 nm excitation is shown in Fig. 7. Upon this excitation dominates emission in the range of 410–450 nm. Corresponding excitation spectrum shows a stronger band peaked at 352 nm and a weaker band about 266 nm (Fig. 7). The luminescence band with a maximum near 390 nm that is efficiently excited about 266 nm can be assigned to 4d95s1 → 4d10 transition of the isolated Ag+ ions [36,37,40,48]. The luminescence band with extended maximum near 410–450 nm that is efficiently excited at 352 nm may be assigned to the Ag+ pair centres and/or the ML-Ag nonplasmonic nanoclusters [37,40,41,44,48,49]. The narrow dip at 402 nm in emission spectra (see Figs. 6 and 7) is related with the 6H5/2 → 6P3/2 excitation transition of the Sm3+ ions. Detailed research of the Ag
Fig. 5. Luminescence excitation spectra of the Li2B4O7:Sm (a) and Li2B4O7:Sm, Ag (b) glasses containing 1.0 mol.% of Sm2O3 registered at T = 295 K by monitoring intensity of emission band at λmon = 598 nm (4G5/2 → 6H7/2 transition).
were attributed to the Sm3+ transitions, denoted in Fig. 5. Observed in the excitation spectra most intense band peaked at 402 nm belongs to the 6H5/2 → 6P3/2 transition. One can notice that the Sm3+ luminescence excitation spectra (Fig. 5) show larger number of the bands with better resolution than the optical absorption spectra (Fig. 2). 3.4. Photoluminescence spectra of Ag centres in the Li2B4O7 glass co-doped with Sm3+ and Ag Usually, the silver impurity introduces in the structure of oxide glasses as Ag+ (4d10) ions, which show photoluminescence [8,22,23,36–38]. Emission band of the Ag+ isolated centres peaked near 355 nm has been observed under excitation at 255 nm in the oxyfluoride glass, doped with Ag [24]. The emission band with maximum about 400 nm belonging to the Ag+ isolated ions was registered upon 270 nm excitation in the sodium-aluminosilicate glass [23]. The Ag+ ions can be reduced to neutral Ag0 (4d105s1) atoms and can form the silver nanoparticles [39] during glass preparation or heat treatment. The neutral Ag0 atoms in glassy SrB4O7 did not show luminescence, but reveal absorption band near 425 nm [40]. Besides this, photoluminescence of the Ag+ pairs [40] and small ML-Ag nanoclusters [41] also can be observed. The Ag+ pairs in the SrB4O7:Ag glass upon excitation of 365 nm reveal broad emission band at 420 nm [40]. Small ML-Ag particles in the soda-lime silicate glasses show broad emission band with a peak at 525 nm under 337 nm excitation [18]. The study of oxyfluoride silicate glass also shows luminescence of the ML-Ag nanoparticles [41]. Particularly, in the emission 293
Journal of Luminescence 213 (2019) 290–296
I.I. Kindrat, et al.
Fig. 9. The luminescence decay curves of Sm3+ centres (4G5/2 → 6H7/2 transition, λmon = 598 nm) in the Li2B4O7:Sm (a) and Li2B4O7:Sm, Ag (b) glasses, registered at T = 295 K under excitation with λexc = 402 nm (6H5/2 → 6P3/2 transition).
Fig. 7. The luminescence excitation (dashed curves) and emission (solid curves) spectra of the Li2B4O7:Sm, Ag glass at T = 295 K. Wavelengths of excitation (λexc) and monitoring (λmon) are denoted in the Figure.
centres in borate glasses will be presented in a separate work. Based on analysis of optical absorption, photoluminescence excitation and emission spectra the diagram of Sm3+ energy levels in the Li2B4O7:Sm, Ag glass is proposed (see Fig. 8). This diagram also shows possible channels of excitation energy transfer from the Ag+ centres and ML-Ag nanoclusters to the Sm3+ centres. 3.5. Decay kinetics of the luminescence centres in Li2B4O7:Sm, Ag glass The luminescence decay curves of Sm3+ emission, which were registered at λexc = 402 nm, λmon = 598 nm, T = 295 K in the Li2B4O7 glasses doped with Sm3+ and co-doped with Sm3+ and Ag are shown in Fig. 9. The registered decay curves are satisfactory fitted by a single exponent function with the lifetime values 2.64 ms and 2.54 ms for the Li2B4O7:Sm and Li2B4O7:Sm, Ag glasses, respectively. The luminescence kinetics of the Ag+ and ML-Ag centres in the Li2B4O7:Sm, Ag glass are given in Fig. 10. The obtained luminescence decay curves show slightly non-exponential nature. Therefore, the mean lifetimes were calculated with usage the following relation [8]:
τmean =
∫ t⋅I (t )⋅dt ∫ I (t )⋅dt
Fig. 10. The luminescence decay curves of Ag+ ions (a) and ML-Ag nanoclusters (b) in the Li2B4O7:Sm, Ag glass. Wavelengths of excitation (λexc) and monitoring (λmon) are denoted in the Figure.
(3)
It was found that the mean lifetime of Ag+ luminescence equals 63 μs. Luminescence kinetics of the ML-Ag nanoclusters in the Li2B4O7:Sm, Ag glass is characterised by slightly greater mean lifetime that equals 117 μs. The obtained lifetime values well correlate with results of our previous article [37], where the non-exponential decay curves with mean values of lifetime 91 μs and 112 μs for Ag+ centres and ML-Ag nanoclusters, respectively, were observed in lithium borate glass, co-doped with Eu and Ag. Besides this, obtained lifetimes are comparable with the following lifetimes 68 μs, 114 μs, and 131 us registered for emission of Ag nanoclusters in fluorophosphate glasses at 420 nm, 550 nm, and 620 nm, respectively [44]. 3.6. Quantum yield of the Sm3+ luminescence in the studied glasses The external quantum yield (QY) of luminescence is defined as ratio of a number of emitted photons to a number of absorbed photons. The QY of the Sm3+ luminescence has been measured experimentally by absolute method using integrating sphere. The external QY as a function of excitation wavelength for the Li2B4O7:Sm and Li2B4O7:Sm, Ag glasses are presented in Fig. 11. One can see that absolute QY of the
Fig. 8. The partial energy diagram of Sm3+ ions in the Sm3+-Ag co-doped Li2B4O7 glass showing luminescence mechanism and energy transfer channels. 294
Journal of Luminescence 213 (2019) 290–296
I.I. Kindrat, et al.
Li2B4O7:Sm, Ag glass is promising orange-red luminescent materials. The main priority of the studied glasses is simple preparation technology allowing to produce large luminescent layers of high transparency that is impracticable for powdered and monocrystalline materials. Such UV–visible photo-conversion layers can be used in the Si solar cells working in the regions with intense UV-radiation including outer space [11]. Thus, the spectroscopic results, presented in this article, including measurements of external QY of the Sm3+ luminescence, can significant extend the application of glasses co-doped with Sm3+ and Ag. 4. Conclusions The lithium tetraborate (Li2B4O7) glasses, doped with Sm3+ and codoped with Sm3+ and Ag have been obtained and studied in detail by conventional EPR and optical spectroscopy methods. On the basis of analysis of obtained results, it is possible to summarise the following:
• The Sm dopant is incorporated into the structure of lithium tetra-
Fig. 11. The dependence of external QY of the Sm3+ luminescence in the Li2B4O7:Sm (a) and Li2B4O7:Sm, Ag (b) glasses as a function of wavelength of photoexcitation.
•
Table 2 External QY of the Sm3+ luminescence in the investigated Li2B4O7:Sm and Li2B4O7:Sm, Ag glasses and some other Sm3+-doped glasses, reported by different authors. Glass composition
QY, %
References
Li2B4O7:Sm Li2B4O7:Sm,Ag CdO–Al2O3–SiO2 Na2O–ZnO–PbO–GeO2–TeO2 Li2O–K2O–BaO–Bi2O3–TeO2 Li2O–Y2O3–Al2O3–SiO2 Li2O–K2O–ZnO–BaO–Sb2O3–B2O3
20.4 29.1 2.52 6.0 7.55 11.58 13.29
this work this work [50] [51] [52] [53] [54]
• • • •
Li2B4O7:Sm, Ag glass upon excitation at 402 nm significantly grows from 20.4% up to 29.1% in comparison with Li2B4O7:Sm glass. Increasing of QY in the Sm3+-Ag co-doped Li2B4O7 glass also is observed under excitations at 475 nm from 12.0% up to 16.6%, 375 nm from 4.2% to 10.2%, and 362 nm from 2.2% to 5.9% (see Fig. 11). The increasing of Sm3+ luminescence QY in the Li2B4O7:Sm, Ag glass in the UV and violet spectral regions is more intense than in the blue and cyan spectral ranges. Strong increasing of absolute QY of Sm3+ luminescence in the Li2B4O7:Sm, Ag glass is associated with transfer of excitation energy from the Ag+ to the Sm3+ centres. The transfer of excitation energy from the Ag+ pair centres and/or ML-Ag nanoclusters to the Sm3+ centres also can be responsible for the Sm3+ luminescence enhancement in the Li2B4O7 glass, co-doped with Sm3+ and Ag. Eventually, effects induced by SPR of the Ag metallic nanoparticles can also lead to increasing of the Sm3+ luminescence intensity. However, in our opinion, mechanism related with plasmonic Ag nanoparticles is insignificant in the investigated Li2B4O7:Sm, Ag glass. Up to present time there are absent articles, which present measurements of external QY of luminescence of the Sm3+ ions in glasses co-doped by Sm3+ and Ag. Recently published articles [17,19–25,27] present increasing of the Sm3+ luminescence intensity in the silver codoped glasses, but have no reported about the QY of luminescence that is essential for applying of luminescent materials in practice. Comparison of the measured luminescence QY with corresponding values, obtained for some other Sm3+-doped glasses, are shown in Table 2. It should be noted that achieved external QY of Sm3+ luminescence in the Sm3+-Ag co-doped Li2B4O7 glass is higher than the QY in other oxide glasses. Hence, it is possible to conclude that the
borate glass exclusively in form of the Sm3+ (4f5, 6H5/2) impurity ions, which reveal typical optical absorption and luminescence spectra. Luminescence emission spectra of the Sm3+ centres in the Li2B4O7 glasses, doped with Sm3+ and co-doped with Sm3+ and Ag show bands belonging to the 4G5/2 → 6HJ (J = 5/2–13/2) 4f – 4f transitions with characteristic decay kinetics. Photoluminescence spectra and decay kinetics of the Ag+ centres and ML-Ag nanoclusters in glass with Li2B4O7:Sm, Ag composition have been registered and analysed. Enhancement of Sm3+ luminescence in the Li2B4O7:Sm, Ag glass was registered as a result of transfer of the excitation energy from the Ag+ centres and the ML-Ag non-plasmonic nanoclusters to the Sm3+. Quantum yield of luminescence of the Sm3+ centres in Li2B4O7:Sm, Ag glass grows from 20.4 to 29.1% as compared with the Li2B4O7:Sm glass. centres The Li2B4O7 glasses co-doped with Sm3+ and Ag are prospective orange-red luminescent materials for different applications, including UV–visible conversion layers.
Acknowledgements This work was partly supported by the Vlokh Institute of Physical Optics (Lviv, Ukraine) in the framework of scientific project No. 0119U100357 of the Ministry of Education and Science of Ukraine. Authors are thankful to M.Sc. I.M. Teslyuk for glasses synthesis and samples preparation. Special thanks to Dr. Y.O. Kulyk from Ivan Franko National University of Lviv (Ukraine) for registration of the XRD patterns. References [1] M. Yamane, Y. Asahara, Glasses for Photonics, Cambridge University Press, 2000, https://doi.org/10.1017/CBO9780511541308. [2] L.D. Pye, V.D. Fréchette, N.J. Kreidl (Eds.), Borate Glasses, Plenum Press, New York, 1978, https://doi.org/10.1007/978-1-4684-3357-9. [3] S. Tanabe, Rare-earth-doped glasses for fiber amplifiers in broadband telecommunication, C.R. Chimie 5 (2002) 815–824 https://doi.org/10.1016/S16310748(02)01449-2. [4] I.I. Kindrat, B.V. Padlyak, A. Drzewiecki, Luminescence properties of the Sm-doped borate glasses, J. Lumin. 166 (2015) 264–275 https://doi.org/10.1016/j.jlumin. 2015.05.051. [5] I.I. Kindrat, B.V. Padlyak, S. Mahlik, B. Kukliński, Y.O. Kulyk, Spectroscopic properties of the Ce-doped borate glasses, Opt. Mater. 59 (2016) 20–27 https://doi.org/ 10.1016/j.optmat.2016.03.053. [6] I.I. Kindrat, B.V. Padlyak, Luminescence properties and quantum efficiency of the Eu-doped borate glasses, Opt. Mater. 77 (2018) 93–103 https://doi.org/10.1016/j. optmat.2018.01.019. [7] G. Blasse, B.C. Grabmaier, Luminescent Materials, Springer Verlag, Berlin, 1994https://doi.org/10.1007/978-3-642-79017-1.
295
Journal of Luminescence 213 (2019) 290–296
I.I. Kindrat, et al.
[32] B.V. Padlyak, W. Ryba-Romanowski, R. Lisiecki, V.T. Adamiv, Ya.V. Burak, I.M. Teslyuk, Synthesis, EPR and optical spectroscopy of the Cr-doped tetraborate glasses, Opt. Mater. 34 (2012) 2112–2119 https://doi.org/10.1016/j.optmat.2012. 06.014. [33] B.V. Padlyak, A. Drzewiecki, Spectroscopy of the CaB4O7 and LiCaBO3 glasses, doped with terbium and dysprosium, J. Non-Cryst. Solids 367 (2013) 58–69 https://doi.org/10.1016/j.jnoncrysol.2013.02.018. [34] G.H. Dieke, H.M. Crosswhite, The spectra of the doubly and triply ionized rare earths, Appl. Opt. 2 (1963) 675–686 https://doi.org/10.1364/AO.2.000675. [35] W.T. Carnall, P.R. Fields, K. Rajnak, Electronic energy levels in the trivalent lanthanide aquo ions. I. Pr3+, Nd3+, Pm3+, Sm3+, Dy3+, Ho3+, Er3+, and Tm3+, J. Chem. Phys. 49 (1968) 4424–4442 https://doi.org/10.1063/1.1669893. [36] B.V. Padlyak, A. Drzewiecki, T.B. Padlyak, V.T. Adamiv, I.M. Teslyuk, Resonant excited UV luminescence of the Gd3+ centres in borate glasses, co-doped with Gd and Ag, Opt. Mater. 79 (2018) 302–309 https://doi.org/10.1016/j.optmat.2018.03. 050. [37] I.I. Kindrat, B.V. Padlyak, B. Kukliński, A. Drzewiecki, V.T. Adamiv, Enhancement of the Eu3+ luminescence in Li2B4O7 glasses co-doped with Eu and Ag, J. Lumin. 204 (2018) 122–129 https://doi.org/10.1016/j.jlumin.2018.07.051. [38] I.I. Kindrat, B.V. Padlyak, R. Lisiecki, V.T. Adamiv, I.M. Teslyuk, Enhancement of the Er3+ luminescence in Er–Ag co-doped Li2B4O7 glasses, Opt. Mater. 85 (2018) 238–245 https://doi.org/10.1016/j.optmat.2018.08.052. [39] A.S. Kuznetsov, V.K. Tikhomirov, M.V. Shestakov, V.V. Moshchalkov, Ag nanocluster functionalized glasses for efficient photonic conversion in light sources, solar cells and flexible screen monitors, Nanoscale 5 (2013) 10065–10075 https:// doi.org/10.1039/c3nr02798h. [40] A. Meijerink, M.M.E. van Heek, G. Blasse, Luminescence of Ag+ in crystalline and glassy SrB4O7, J. Phys. Chem. Solids 54 (1993) 901–906 https://doi.org/10.1016/ 0022-3697(93)90216-E. [41] H. Guo, X.F. Wang, J.D. Chen, F. Li, Ultraviolet light induced white light emission in Ag and Eu3+ co-doped oxyfluoride glasses, Optic Express 18 (2010) 18900–18905 https://doi.org/10.1364/OE.18.018900. [42] H. Zhong, B. Chen, S. Fu, X. Li, J. Zhang, S. Xu, Y. Zhang, L. Tong, G. Sui, H. Xia, Broadband emission and flat optical gain glass containing Ag aggregates for tunable laser, J. Am. Ceram. Soc. 102 (2019) 1150–1156 https://doi.org/10.1111/jace. 16006. [43] X. Li, H. Zhong, B. Chen, G. Sui, J. Sun, S. Xu, L. Cheng, J. Zhang, Highly stable and tunable white luminescence from Ag-Eu3+ co-doped fluoroborate glass phosphors combined with violet LED, Optic Express 26 (2018) 1870–1881 https://doi.org/10. 1364/OE.26.001870. [44] H. Fares, T. Castro, J.R. Orives, D.F. Franco, M. Nalin, White light and multicolor emission tuning in Ag nanocluster doped fluorophosphate glasses, RSC Adv. 7 (2017) 44356–44365 https://doi.org/10.1039/C7RA08778K. [45] H. Fares, S.N.C. Santos, M.V. Santos, D.F. Franco, A.E. Souza, D. Manzani, C.R. Mendonça, M. Nalin, Highly luminescent silver nanocluster-doped fluorophosphate glasses for microfabrication of 3D waveguides, RSC Adv. 7 (2017) 55935–55944 https://doi.org/10.1039/C7RA11792B. [46] Y. Petit, C.-H. Park, J.-M. Mok, E. Smetanina, B. Chimier, G. Duchateau, T. Cardinal, L. Canioni, S.-H. Park, Ultrashort laser induced spatial redistribution of silver species and nano-patterning of etching selectivity in silver-containing glasses, Optic Express 27 (2019) 13765 13680 https://doi.org/10.1364/OE.27.013675. [47] I.I. Kindrat, B.V. Padlyak, A. Drzewiecki, Intrinsic luminescence of un-doped borate glasses, J. Lumin. 187 (2017) 546–554 https://doi.org/10.1016/j.jlumin.2017.03. 071. [48] R.F. Wei, J.J. Li, J.Y. Gao, H. Guo, Enhancement of Eu3+ luminescence by Ag species (Ag NPs, ML-Ag, Ag+) in oxyfluoride glasses, J. Am. Ceram. Soc. 95 (2012) 3380–3382 https://doi.org/10.1111/j.1551-2916.2012.05459.x. [49] R. Ma, J. Gao, Q. Xu, S. Cui, X. Qiao, J. Du, X. Fan, Eu2+ promoted formation of molecule-like Ag and enhanced white luminescence of Ag/Eu-codoped oxyfluoride glasses, J. Non-Cryst. Solids 432 (2016) 348–353 https://doi.org/10.1016/j. jnoncrysol.2015.10.032. [50] Y. Lei, F.F. Fu, L. Zheng, Z.Q. Wang, X. Zhao, H. Lin, Absolute luminous flux and quantum yield of Sm3+-doped cadmium-aluminum-silicate glasses under the pumping of blue light emitting diode, Appl. Mech. Mater. 275–277 (2013) 1974–1977 https://doi.org/10.4028/www.scientific.net/AMM.275-277.1974. [51] F. Wang, B.J. Chen, H. Lin, E.Y.B. Pun, Spectroscopic properties and external quantum yield of Sm3+ doped germanotellurite glasses, J. Quant. Spectrosc. Radiat. Transfer 147 (2014) 63–70 https://doi.org/10.1016/j.jqsrt.2014.05.014. [52] H. Lin, X.Y. Wang, C.M. Li, X.J. Li, S. Tanabe, J.Y. Yu, Spectral power distribution and quantum yields of Sm3+-doped heavy metal tellurite glass under the pumping of blue lighting emitting diode, Spectrochim. Acta A 67 (2007) 1417–1420 https:// doi.org/10.1016/j.saa.2006.10.039. [53] F. Fu, B. Chen, L. Shen, E.Y.B. Pun, H. Lin, Multi-channel transition emissions of Sm3+ in lithium yttrium aluminum silicate glasses and derived opalescent glass ceramics, J. Alloy. Comp. 582 (2014) 265–272 https://doi.org/10.1016/j.jallcom. 2013.08.040. [54] L.F. Shen, B.J. Chen, E.Y.B. Pun, H. Lin, Sm3+-doped alkaline earth borate glasses as UV → visible photon conversion layer for solar cells, J. Lumin. 160 (2015) 138–144 https://doi.org/10.1016/j.jlumin.2014.11.052.
[8] W.M. Yen, Sh. Shionoya, H. Yamamoto (Eds.), Phosphor Handbook, CRC Press, Boca Raton, 2007, https://doi.org/10.1201/9781420005233. [9] C.K. Jayasankar, P. Babu, Optical properties of Sm ions in lithium borate and lithium fluoroborate glasses, J. Alloy. Comp. 307 (2000) 82–95 https://doi.org/10. 1016/S0925-8388(00)00888-4. [10] P. Kaur, S. Kaur, G.P. Singh, D.P. Singh, Sm3+ doped lithium aluminoborate glasses for orange coloured visible laser host material, Solid State Commun. 171 (2013) 22–25 https://doi.org/10.1016/j.ssc.2013.07.021. [11] I.I. Kindrat, B.V. Padlyak, R. Lisiecki, Judd–Ofelt analysis and radiative properties of the Sm3+ centres in Li2B4O7, CaB4O7, and LiCaBO3 glasses, Opt. Mater. 49 (2015) 241–248 https://doi.org/10.1016/j.optmat.2015.09.024. [12] B.V. Padlyak, I.I. Kindrat, R. Lisiecki, V.T. Adamiv, I.M. Teslyuk, New effective luminescent materials based on the Sm-doped borate glasses, Adv. Mater. Lett. 8 (2017) 723–734 https://doi.org/10.5185/amlett.2017.1436. [13] C. Jiang, Y. Huang, S. Park, K. Jang, H.J. Seo, Luminescence and spectral hole burning of Sm2+ doped in Li2O–SrO–B2O3 glass-ceramics, Spectrochim. Acta A 72 (2009) 412–416 https://doi.org/10.1016/j.saa.2008.10.014. [14] H. Song, M. Nogami, Room-temperature hole-burning and sublinear hole-growth dynamics in an Sm2+-doped aluminosilicate glass, J. Non-Cryst. Solids 297 (2002) 113–119 https://doi.org/10.1016/S0022-3093(01)01035-3. [15] V.C. Costa, Y. Shen, A.M.M. Santos, K.L. Bray, Luminescence measurements on Sm2+-doped sol–gel glasses, J. Non-Cryst. Solids 304 (2002) 238–243 https://doi. org/10.1016/S0022-3093(02)01029-3. [16] O.L. Malta, P.A. Santa-Cruz, G.F. De Sá, F. Auzel, Fluorescence enhancement induced by the presence of small silver particles in Eu3+ doped materials, J. Lumin. 33 (1985) 261–272 https://doi.org/10.1016/0022-2313(85)90003-1. [17] J.A. Jiménez, S. Lysenko, H. Liu, M. Sendova, Luminescence of trivalent samarium ions in silver and tin co-doped aluminophosphate glass, Opt. Mater. 33 (2011) 1215–1220 https://doi.org/10.1016/j.optmat.2011.02.013. [18] M. Eichelbaum, K. Rademann, Plasmonic enhancement or energy transfer? On the luminescence of gold-, silver-, and lanthanide-doped silicate glasses and its potential for light-emitting devices, Adv. Funct. Mater. 19 (2009) 2045–2052 https://doi. org/10.1002/adfm.200801892. [19] M.R. Dousti, Plasmonic effect of silver nanoparticles on the upconversion emissions of Sm3+-doped sodium-borosilicate glass, Measurement 56 (2014) 117–120 https://doi.org/10.1016/j.measurement.2014.06.024. [20] I. Mechergui, H. Fares, S.A. Mohamed, M. Nalin, H. Elhouichet, Coupling between surface plasmon resonance and Sm3+ ions induced enhancement of luminescence properties in fluoro-tellurite glasses, J. Lumin. 190 (2017) 518–524 https://doi. org/10.1016/j.jlumin.2017.06.013. [21] S.Q. Mawlud, A comparative enhancement of Au and Ag NPs role on radiative properties in Sm3+ doped zinc-sodium tellurite glass: Judd-Ofelt parameter, Spectrochim. Acta A 209 (2019) 78–84 https://doi.org/10.1016/j.saa.2018.10.032. [22] G.E. Malashkevich, A.V. Semchenko, A.A. Sukhodola, A.P. Stupak, A.V. Sukhodolov, B.V. Plyushch, V.V. Sidskiĭ, G.A. Denisenko, Influence of silver on the Sm3+ luminescence in “Aerosil” silica glasses, Phys. Solid State 50 (2008) 1464–1472 https://doi.org/10.1134/S1063783408080131. [23] L. Li, Y. Yang, D. Zhou, Z. Yang, X. Xu, J. Qiu, Investigation of the role of silver species on spectroscopic features of Sm3+-activated sodium–aluminosilicate glasses via Ag+-Na+ ion exchange, J. Appl. Phys. 113 (2013) 193103https://doi.org/10. 1063/1.4807313. [24] J.J. Li, R.F. Wei, X.Y. Liu, H. Guo, Enhanced luminescence via energy transfer from Ag+ to RE ions (Dy3+, Sm3+, Tb3+) in glasses, Optic Express 20 (2012) 10122–10127 https://doi.org/10.1364/OE.20.010122. [25] S. Thomas, M.S. Sajna, Sk.N. Rasool, M. Gopinath, C. Joseph, N.V. Unnikrishnan, Sm3+-doped fluorophosphate glass: formation of Ag nanoparticles via Ag+/K+ ion exchange and their effects on optical and dielectric properties, Opt. Mater. 39 (2015) 167–172 https://doi.org/10.1016/j.optmat.2014.11.019. [26] M. Dyrba, P.-T. Miclea, S. Schweizer, Surface plasmons for fluorescence enhancement in Sm-doped borate glasses, Radiat. Meas. 45 (2010) 314–316 https://doi. org/10.1016/j.radmeas.2010.01.028. [27] Y. Gao, S. Murai, K. Fujita, K. Tanaka, Visible and near-infrared photoluminescence enhanced by Ag nanoparticles in Sm3+-doped aluminoborate glass, Opt. Mater. 86 (2018) 611–616 https://doi.org/10.1016/j.optmat.2018.10.018. [28] B.V. Padlyak, S.I. Mudry, Y.O. Kulyk, A. Drzewiecki, V.T. Adamiv, Y.V. Burak, I.M. Teslyuk, Synthesis and X-ray structural investigation of undoped borate glasses, Mater. Sci. Pol. 30 (2012) 264–273 https://doi.org/10.2478/s13536-012-0032-1. [29] A.T. Brant, B.E. Kananan, M.K. Murari, J.W. McClory, J.C. Petrosky, V.T. Adamiv, Ya.V. Burak, P.A. Dowben, L.E. Halliburton, Electron and hole traps in Ag-doped lithium tetraborate (Li2B4O7) crystals, J. Appl. Phys. 110 (2011) 093719https://doi. org/10.1063/1.3658264. [30] A.T. Brant, D.A. Buchanan, J.W. McClory, V.T. Adamiv, Ya.V. Burak, L.E. Halliburton, N.C. Giles, Photoluminescence from Ag2+ ions in lithium tetraborate (Li2B4O7) crystals, J. Lumin. 153 (2014) 79–84 https://doi.org/10.1016/j. jlumin.2014.03.008. [31] B.E. Kananen, E.S. Maniego, E.M. Golden, N.C. Giles, J.W. McClory, V.T. Adamiv, Ya.V. Burak, L.E. Halliburton, Optically stimulated luminescence (OSL) from Agdoped Li2B4O7 crystals, J. Lumin. 177 (2016) 190–196 https://doi.org/10.1016/j. jlumin.2016.04.032.
296
Contents lists available at ScienceDirect
Journal of Luminescence journal homepage: www.elsevier.com/locate/jlumin
Effect of silver co-doping on enhancement of the Sm3+ luminescence in lithium tetraborate glass
T
I.I. Kindrata, B.V. Padlyaka,b,∗, B. Kuklińskic, A. Drzewieckia, V.T. Adamivb a
University of Zielona Góra, Institute of Physics, 4a Szafrana Str., 65-516, Zielona Góra, Poland Vlokh Institute of Physical Optics, Department of Optical Materials, 23 Dragomanov Str., 79-005, Lviv, Ukraine c University of Gdańsk, Institute of Experimental Physics, 57 Wita Stwosza Str., 80-308, Gdańsk, Poland b
A R T I C LE I N FO
A B S T R A C T
Keywords: Borate glasses Sm3+ ions Luminescence spectra Ag+ ions Silver nanoparticles Quantum yield
Luminescent properties of the Sm3+-doped and Sm3+-Ag co-doped glasses with Li2B4O7 (or Li2O–2B2O3) basic composition are investigated and analysed. Spectroscopic properties of the obtained Li2B4O7:Sm and Li2B4O7:Sm, Ag glasses were studied using measurements of optical absorption, electron paramagnetic resonance (EPR), photoluminescence (excitation, emission, decay kinetics), and quantum yield (QY) via an absolute method. Optical absorption spectra exhibit absorption bands related with transitions from the ground 6H5/2 state of Sm3+ ions to several excited states. Photoluminescence spectra of the Sm3+-doped glasses reveal emission bands, which correspond to the 4G5/2 → 6HJ (J = 5/2–13/2) transitions of Sm3+ ions. Luminescence excitation spectra and decay curves of the Sm3+ luminescence also have been analysed. The EPR study confirms presence of Ag species in the Sm3+-Ag co-doped samples. Photoluminescence emission and excitation spectra and luminescence decay kinetics of the Ag+ ions and small non-plasmonic molecule-like silver (ML-Ag) nanoclusters are observed and discussed. Enhancement of Sm3+ luminescence in the Li2B4O7:Sm, Ag glass has been observed. Measurements confirm the increasing of external QY of the Sm3+ luminescence in 1.43 times in the Ag co-doped glass. Such enhancement of the luminescence is attributed to the excitation energy transfer from Ag+ ions and ML-Ag nanoclusters to the Sm3+ ions. The obtained high QY of the Sm3+ luminescence shows that Li2B4O7:Sm, Ag glasses belong to promising luminescent materials.
1. Introduction In the last decades, the studies of borate glasses represents significant practical interest, because these glasses reveal attractive optical and spectroscopic properties [1–6]. Practical interest to borate glasses, generally, is caused by two aspects. At first, glassy borate compounds are more promising materials than corresponding crystals thank to simple and inexpensive producing technology. At second, the network of borate glasses allows to incorporate considerably higher amount of the impurity lanthanide (Ln) ions in comparison with their crystalline analogies. At present time special interest represent borate glasses with Li2O–2B2O3 basic composition that is identical to the well-known lithium tetraborate (Li2B4O7) crystal [4–6]. Attractive luminescent properties of materials doped with lanthanide ions, including Sm3+ ions, initiated potentialities for their wide practical application e.g. in solid-state lighting, laser technique, energy transformers, sensors, displays, telecommunication devices, etc. [7,8]. The Sm3+ (4f5, 6H5/2) ions in oxide glasses reveal characteristic intense
∗
yellow, orange, and red emission bands, which are related to the 4G5/ 6 4 6 4 6 2 → H5/2, G5/2 → H7/2, and G5/2 → H9/2 emission transitions, respectively. Up to present time, the luminescent properties of different Sm3+-doped borate glasses were widely studied and reported in number papers, notably in Refs. [9–12]. The luminescent properties of the Sm2+ (4f6, 7F0) ions in oxide glasses were published only in few articles [13–15]. Luminescence of Sm2+ ions is characterised by broad emission in the red spectral region. Generally, the Sm2+ stable ions can be formed in glasses only during synthesis in strongly reduced atmospheres [14,15], whereas the Sm2+ ions created by X- or γ-radiation are unstable [13,14]. The Sm3+ ions reveal abovementioned efficient photoluminescence. However, cross-section of the Sm3+ absorption transitions, particularly in the ultraviolet (UV) region, is not very high due to the parity forbidden 4f – 4f transitions. Therefore, additional approaches are required in order to increase the light output of the Sm3+ luminescence. At present time, co-doping with silver is investigated as an attractive approach to improve the luminescence output of lanthanide ions.
Corresponding author.University of Zielona Góra, Institute of Physics, 4a Szafrana Str., 65-516, Zielona Góra, Poland. E-mail address: [email protected] (B.V. Padlyak).
https://doi.org/10.1016/j.jlumin.2019.05.045 Received 14 April 2019; Received in revised form 16 May 2019; Accepted 17 May 2019 Available online 20 May 2019 0022-2313/ © 2019 Elsevier B.V. All rights reserved.
Journal of Luminescence 213 (2019) 290–296
I.I. Kindrat, et al.
Enhanced luminescence of Eu3+ ions as a result of the local-field effect, caused by surface plasmon resonance (SPR) of the Ag nanoparticles was observed in the CaF2–B2O3 glass by Malta et al. [16]. Jiménez et al. [17] report enhanced Sm3+ photoluminescence in aluminophosphate glass co-doped with Ag due to the energy transfer from the Ag+ to Sm3+ centres. Transfer of excitation energy from non-plasmonic moleculelike gold and silver particles to the Ln3+ ions was noticed for the first time in soda-lime silicate glasses by Eichelbaum and Rademann [18]. Currently three different processes of the Ln3+ luminescence enhancement in the co-doped with Ln and Ag glasses had been proposed. Up to present time, enhancement of the Sm3+ luminescence related with SPR effect was reported in sodium borosilicate [19], heavy metal fluorotellurite [20], and sodium-zinc tellurite [21] glasses. It should be noted that a quenching effect of Sm3+ photoluminescence with the presence of metallic silver nanoparticles was reported in Refs. [22,23]. Transfer of the excitation energy from Ag+ to Sm3+ centres was stated in oxyfluoride [24] and fluorophosphate [25] glasses. At last, the excitation energy transfer from different silver species to Sm3+ ions have been observed in sodium-aluminosilicate glass [23]. The number of studies of borate glasses co-doped with Sm3+ and Ag is very limited at present time. Dyrba et al. [26] observe SPR-related absorption band of silver nanoparticles in lithium and sodium borate glasses. However, it was concluded that influence of plasmon resonance in these glasses is too small to enhance the fluorescence emission [26]. In previous year, scientists from Kyoto University report study of Sm3+doped aluminoborate glass containing Ag nanoparticles [27]. The intensity of visible Sm3+ photoluminescence near 600 nm was enhanced under excitation at 400 nm in 1.398 times [27]. The enhancement was ascribed to the SPR of Ag nanoparticles [27]. Luminescent properties of the Sm3+-doped borate glasses with different compositions (Li2B4O7, LiKB4O7, CaB4O7, and LiCaBO3) preliminary have been studied by us in Ref. [4]. Attractive results were obtained for the Sm3+-doped lithium tetraborate (Li2B4O7:Sm) glass that reveals highest quantum yield (QY) of luminescence among the investigated glasses [12]. Consequently, the main aim of this article is to investigate the effect of silver co-doping on the possibility to enhance of the Sm3+ luminescence in the lithium tetraborate glasses. This paper mainly is focused on the analysis of luminescence QY in the Li2B4O7 glasses, doped with Sm3+ and co-doped with Sm3+ and Ag as well as mechanisms related to the Sm3+ photoluminescence enhancing, caused by the Ag dopant.
Fig. 1. The XRD patterns of the Li2B4O7:Sm (a) and Li2B4O7:Sm, Ag (b) glasses.
polished to the approximate size of 10 mm × 7 mm × 2 mm. For electron paramagnetic resonance (EPR) investigation the obtained glass samples were cut to the approximate size of 5 mm × 3 mm × 2 mm. 2.2. Experimental equipment The XRD (X-ray diffraction) investigations were performed with usage commercial X-ray diffractometer (model DRON-3) controlled by computer. The XRD patterns of the Li2B4O7:Sm and Li2B4O7:Sm, Ag glasses are presented in Fig. 1. Obtained diffractograms show typical glassy-like pattern without any discrete sharp peaks that confirms disordered glass structure of the investigated Li2B4O7:Sm and Li2B4O7:Sm, Ag samples. Optical absorption spectra were registered with usage Shimadzu (model UV-2600) spectrophotometer. Emission and luminescence excitation spectra as well as decay curves were registered using Horiba Yvon (model FluoroMax–4) spectrofluorimeter. The luminescence spectra and kinetics were registered at room temperature with usage the same holder for solid bulk sample. Excitation and monitoring wavelengths for registered luminescence spectra are indicated in corresponding figures. The quantum yield of luminescence was registered by Hamamatsu Quantaurus-QY Absolute PL quantum yield spectrometer (model C11347). Paramagnetic centres have been registered with usage commercial X-band “Radiopan” (Poland) EPR spectrometer (model SE/X-2013) controlled by computer. The effective g-factor (geff) of observed EPR signals was calculated using the following relation:
2. Experimental details 2.1. Borate glasses synthesis and samples preparation The Li2B4O7 glasses doped with Sm3+ and co-doped with Sm3+ and Ag were produced using standard melt-quenching glass technology [28]. Initially, the mixture of the Li2CO3 and H3BO3, taken in the stoichiometric proportion, has been prepared. The Li2B4O7 powdered compound was synthesised in the air using the following multi-step heating reaction: 4H2 O↑
geff =
(2)
where h is the Planck constant, μB is the Bohr magneton, Br is the resonance magnetic field, and ν is the working frequency of EPR spectrometer.
2H2 O↑
Li2 CO3 + 4H3 BO3 →o Li2 CO3 + 4(α − НВО2) →o 170 C
hν μB Br
250 C
CO2 ↑
Li2 CO3 +2B2 O3 →o Li2 B4 O7 800 C
3. Results and discussion
(1)
3.1. The optical absorption spectra
Then, the Sm2O3 in amount of 1.0 mol.% (for obtaining of the Li2B4O7:Sm glass) or Sm2O3 in amount of 1.0 mol.% and AgNO3 in amount 2.0 mol.% (for obtaining of the Li2B4O7:Sm, Ag glass) were added to the as-synthesised Li2B4O7 powdered compound and thoroughly mixed. Obtained mixtures were heated and melted in a corundum ceramic crucible. Large samples of the Li2B4O7 glasses doped with Sm3+ and co-doped with Sm3+ and Ag of high chemical purity and optical quality were obtained by quick cooling of the corresponding melts. The bulk glass samples for optical measurements were cut and
Optical absorption spectra of the Li2B4O7 glasses doped with Sm3+ and co-doped with Sm3+ and Ag, registered in the 300–800 nm spectral range are presented in Fig. 2. Significant increasing of optical absorption below 340 nm is attributed to the fundamental absorption edge of the glass matrix. In registered absorption spectra have been observed several bands of weak intensity belonging to the Sm3+ ions (see inset in Fig. 2). The most intense absorption band that is peaked about 402 nm 291
Journal of Luminescence 213 (2019) 290–296
I.I. Kindrat, et al.
Fig. 3. The X-band EPR spectra of the Li2B4O7:Sm (a) and Li2B4O7:Sm, Ag (b) glasses, recorded at T = 295 K. Fig. 2. The optical absorption spectra of the Li2B4O7:Sm (a) and Li2B4O7:Sm, Ag (b) glasses, recorded at T = 295 K in the range of 300–800 nm.
inhomogeneously broadened signals of isolated Ag0 and Ag2+ centres as well as their paramagnetic nanoclusters and aggregates with unresolved HF and SHF structures.
corresponds to the 6H5/2 → 6P3/2 transition. Spectrum of optical absorption of the Li2B4O7:Sm, Ag glass reveals additional weak band in the 410–425 nm range (Fig. 2). The broadband absorption peaked near 418 nm is assigned to the SPR (surface plasmon resonance) of the Ag metallic nanoparticles, or most precisely – resonant oscillations of the conduction electrons in the Ag nanoparticles, stimulated by an incident light. It is worth noting that registered SPR band intensity in several dozen times is less than intensities of SPR bands with maxima located between 436 and 450 nm in sodium borosilicate glass [19], around 430 nm in lithium and sodium borate glasses [26], and about 425 nm in aluminoborate glass [27]. Hence, the amount of silver nanoparticles (Ag0) in the investigated Li2B4O7:Sm, Ag glass is relatively small.
3.3. Luminescence emission and excitation spectra of the Sm3+ ions In Fig. 4 are presented the Sm3+ emission spectra in the Li2B4O7 glasses doped with Sm3+ (1.0 mol.% of Sm2O3) and co-doped with Sm3+ (1.0 mol.% of Sm2O3) and Ag (2.0 mol.% of AgNO3). The Sm3+ emission intensity in the Li2B4O7:Sm, Ag glass increases in 1.5 times in comparison with Li2B4O7:Sm glass, but the form of emission bands are much the same. The Sm3+ emission spectra reveal three intense bands in the 550–670 nm region and two weak bands in the 670–820 nm range (Table 1). The observed bands refer to 4G5/2 → 6HJ (J = 5/2, 7/2, 9/2, 11/2, and 13/2) emission transitions of the Sm3+ centres, which are denoted in Fig. 4. Excitation spectra of the Sm3+-doped and Sm3+-Ag co-doped Li2B4O7 glasses, registered at T = 295 K by monitoring of luminescence intensity at λmon = 598 nm are given in Fig. 5. The Ag co-doping causes the raising of intensities of excitation bands in the Li2B4O7:Sm, Ag glass. Observed in the excitation spectra bands according to Refs. [34,35]
3.2. EPR spectroscopy of the Li2B4O7:Sm, Ag glass The impurity of samarium can reveals in oxide compounds as paramagnetic Sm3+ (4f5, 6H5/2) Kramers ions and Sm2+ (4f6, 7F0) nonKramers ions. The isolated Sm3+ ions in the Li2B4O7 glass show asymmetric broad EPR signal with geff ≅ 9.7 observed only at low temperatures (T ≤ 20 K) [4]. The silver dopant into the structure of oxide compounds can be incorporated as Ag2+ (4d9, 2D5/2), Ag+ (4d10, 1 S0), and Ag0 (4d105s1, 2S1/2) ions. The paramagnetic Ag2+ and Ag0 ions can be detected by EPR. Isolated Ag2+ ions in EPR spectra of the Li2B4O7:Ag crystals [29–31] show characteristic doublets, cause by hyperfine (HF) interactions of electron spin S = 1/2 with nuclear spin I = 1/2 of both 107Ag and 109Ag isotopes. Isolated Ag0 ions in Li2B4O7:Ag crystals reveal 16 lines as a result of HF interaction of electron spin with the 107Ag and 109Ag nuclei (I = 1/2) and superhyperfine (SHF) interaction with nuclei of 11B (I = 3/2) [29–31]. In Fig. 3 are presented the X-band EPR spectra of the Li2B4O7 glasses, doped with Sm3+ and co-doped with Sm3+ and Ag. In the Li2B4O7:Sm and Li2B4O7:Sm, Ag glasses has been registered the sharp EPR signal with the following parameters: geff = 4.296 ± 0.005 and peak-to-peak derivative linewidth ΔBpp = (7.7 ± 0.5) mT as well as geff = 4.297 ± 0.005 and ΔBpp = (7.8 ± 0.5) mT, respectively. Observed signal is typical for glass network and according to Refs. [4,32,33] is attributed to the non-controlled Fe3+ (3d5, 6S5/2) isolated ions, which are localised in the octahedral and/or tetrahedral sites with a strong rhombic distortion. Broad unresolved complex EPR signal with geff = 2.07 ± 0.01 and ΔBpp = (88 ± 5) mT that is observed only in the Li2B4O7:Sm, Ag glass (see Fig. 3) belongs to the superposition of
Fig. 4. The luminescence emission spectra of the Li2B4O7:Sm (a) and Li2B4O7:Sm, Ag (b) glasses containing 1.0 mol.% Sm2O3, registered under excitation with λexc = 402 nm (6H5/2 → 6P3/2 transition) at T = 295 K. 292
Journal of Luminescence 213 (2019) 290–296
I.I. Kindrat, et al.
Table 1 The peak position (λmax), full width at high maximum (FWHM) and luminescence branching ratio (β) of emission bands in the Sm3+-doped and Sm3+-Ag co-doped Li2B4O7 glasses. Transitions
G5/2 → 6H5/2 G5/2 → 6H7/2 4 G5/2 → 6H9/2 4 G5/2 → 6H11/2 4 G5/2 → 6H13/2 4 4
Li2B4O7:Sm
Li2B4O7:Sm,Ag
λmax (nm)
FWHM (cm−1)
β
λmax (nm)
FWHM (cm−1)
β
562 598 645 705 790
289 281 271 553 680
0.210 0.549 0.218 0.022 0.001
562 598 645 704 787
283 294 276 563 690
0.206 0.555 0.216 0.022 0.001
Fig. 6. The luminescence emission spectra of the Li2B4O7:Sm (a) glass as well as luminescence excitation (dashed curves) and emission (solid curves) spectra of the Li2B4O7:Sm, Ag (b) glass at T = 295 K. Wavelengths of excitation (λexc) and monitoring (λmon) are denoted in the Figure.
spectrum upon 352 nm excitation has been observed a broad band peaked at 440 nm [41]. Recently, the strong broad emission from 400 nm to 700 nm ascribed to silver aggregates or silver nanoclusters was observed in calcium borate [42], calcium fluoroborate [43], and multicomponent fluorophosphate [44,45] glasses. Generally, silver dopant in glass network gives positive influence for energy transfer effects, improving of colour coordinates, generation of white light or tuneable emission [42,44]. But, as it was mentioned above, the quenching of Sm3+ luminescence in glasses co-doped with Ag also can be observed [22,23]. Therefore, here it is worth noting the new interesting results [46] about possibility of spatial redistribution of silver species in phosphate glass induced by a femtosecond laser. The luminescence emission spectra of the Li2B4O7:Sm and Li2B4O7:Sm, Ag glasses registered upon excitation of 266 nm are given in Fig. 6. The Li2B4O7:Sm glass shows broadband intrinsic luminescence with a peak near 465 nm and the Sm3+ emission bands in the 550–720 nm spectral region. The intrinsic luminescence of un-doped borate glasses has been investigated in details by us in Ref. [47]. The broadband intrinsic luminescence peaked about 470–490 nm was observed in the Li2B4O7, LiKB4O7, CaB4O7, and LiCaBO3 glasses under excitation at 270 nm [47]. The intrinsic emission band peaked about 470–490 nm in the un-doped borate glasses is related to recombination of the UV-generated O− hole centres with electrons [47]. In the Li2B4O7:Sm, Ag glass, intense photoluminescence of silver dopant was observed in the range of 350–500 nm (see Fig. 6). Observed emission of Ag dopant consists of a strong band near 390 nm and a weaker band about 410–450 nm. The excitation spectrum reveals a broad band peaked near 266 nm. The luminescence emission spectrum of the Li2B4O7:Sm, Ag glass registered under 352 nm excitation is shown in Fig. 7. Upon this excitation dominates emission in the range of 410–450 nm. Corresponding excitation spectrum shows a stronger band peaked at 352 nm and a weaker band about 266 nm (Fig. 7). The luminescence band with a maximum near 390 nm that is efficiently excited about 266 nm can be assigned to 4d95s1 → 4d10 transition of the isolated Ag+ ions [36,37,40,48]. The luminescence band with extended maximum near 410–450 nm that is efficiently excited at 352 nm may be assigned to the Ag+ pair centres and/or the ML-Ag nonplasmonic nanoclusters [37,40,41,44,48,49]. The narrow dip at 402 nm in emission spectra (see Figs. 6 and 7) is related with the 6H5/2 → 6P3/2 excitation transition of the Sm3+ ions. Detailed research of the Ag
Fig. 5. Luminescence excitation spectra of the Li2B4O7:Sm (a) and Li2B4O7:Sm, Ag (b) glasses containing 1.0 mol.% of Sm2O3 registered at T = 295 K by monitoring intensity of emission band at λmon = 598 nm (4G5/2 → 6H7/2 transition).
were attributed to the Sm3+ transitions, denoted in Fig. 5. Observed in the excitation spectra most intense band peaked at 402 nm belongs to the 6H5/2 → 6P3/2 transition. One can notice that the Sm3+ luminescence excitation spectra (Fig. 5) show larger number of the bands with better resolution than the optical absorption spectra (Fig. 2). 3.4. Photoluminescence spectra of Ag centres in the Li2B4O7 glass co-doped with Sm3+ and Ag Usually, the silver impurity introduces in the structure of oxide glasses as Ag+ (4d10) ions, which show photoluminescence [8,22,23,36–38]. Emission band of the Ag+ isolated centres peaked near 355 nm has been observed under excitation at 255 nm in the oxyfluoride glass, doped with Ag [24]. The emission band with maximum about 400 nm belonging to the Ag+ isolated ions was registered upon 270 nm excitation in the sodium-aluminosilicate glass [23]. The Ag+ ions can be reduced to neutral Ag0 (4d105s1) atoms and can form the silver nanoparticles [39] during glass preparation or heat treatment. The neutral Ag0 atoms in glassy SrB4O7 did not show luminescence, but reveal absorption band near 425 nm [40]. Besides this, photoluminescence of the Ag+ pairs [40] and small ML-Ag nanoclusters [41] also can be observed. The Ag+ pairs in the SrB4O7:Ag glass upon excitation of 365 nm reveal broad emission band at 420 nm [40]. Small ML-Ag particles in the soda-lime silicate glasses show broad emission band with a peak at 525 nm under 337 nm excitation [18]. The study of oxyfluoride silicate glass also shows luminescence of the ML-Ag nanoparticles [41]. Particularly, in the emission 293
Journal of Luminescence 213 (2019) 290–296
I.I. Kindrat, et al.
Fig. 9. The luminescence decay curves of Sm3+ centres (4G5/2 → 6H7/2 transition, λmon = 598 nm) in the Li2B4O7:Sm (a) and Li2B4O7:Sm, Ag (b) glasses, registered at T = 295 K under excitation with λexc = 402 nm (6H5/2 → 6P3/2 transition).
Fig. 7. The luminescence excitation (dashed curves) and emission (solid curves) spectra of the Li2B4O7:Sm, Ag glass at T = 295 K. Wavelengths of excitation (λexc) and monitoring (λmon) are denoted in the Figure.
centres in borate glasses will be presented in a separate work. Based on analysis of optical absorption, photoluminescence excitation and emission spectra the diagram of Sm3+ energy levels in the Li2B4O7:Sm, Ag glass is proposed (see Fig. 8). This diagram also shows possible channels of excitation energy transfer from the Ag+ centres and ML-Ag nanoclusters to the Sm3+ centres. 3.5. Decay kinetics of the luminescence centres in Li2B4O7:Sm, Ag glass The luminescence decay curves of Sm3+ emission, which were registered at λexc = 402 nm, λmon = 598 nm, T = 295 K in the Li2B4O7 glasses doped with Sm3+ and co-doped with Sm3+ and Ag are shown in Fig. 9. The registered decay curves are satisfactory fitted by a single exponent function with the lifetime values 2.64 ms and 2.54 ms for the Li2B4O7:Sm and Li2B4O7:Sm, Ag glasses, respectively. The luminescence kinetics of the Ag+ and ML-Ag centres in the Li2B4O7:Sm, Ag glass are given in Fig. 10. The obtained luminescence decay curves show slightly non-exponential nature. Therefore, the mean lifetimes were calculated with usage the following relation [8]:
τmean =
∫ t⋅I (t )⋅dt ∫ I (t )⋅dt
Fig. 10. The luminescence decay curves of Ag+ ions (a) and ML-Ag nanoclusters (b) in the Li2B4O7:Sm, Ag glass. Wavelengths of excitation (λexc) and monitoring (λmon) are denoted in the Figure.
(3)
It was found that the mean lifetime of Ag+ luminescence equals 63 μs. Luminescence kinetics of the ML-Ag nanoclusters in the Li2B4O7:Sm, Ag glass is characterised by slightly greater mean lifetime that equals 117 μs. The obtained lifetime values well correlate with results of our previous article [37], where the non-exponential decay curves with mean values of lifetime 91 μs and 112 μs for Ag+ centres and ML-Ag nanoclusters, respectively, were observed in lithium borate glass, co-doped with Eu and Ag. Besides this, obtained lifetimes are comparable with the following lifetimes 68 μs, 114 μs, and 131 us registered for emission of Ag nanoclusters in fluorophosphate glasses at 420 nm, 550 nm, and 620 nm, respectively [44]. 3.6. Quantum yield of the Sm3+ luminescence in the studied glasses The external quantum yield (QY) of luminescence is defined as ratio of a number of emitted photons to a number of absorbed photons. The QY of the Sm3+ luminescence has been measured experimentally by absolute method using integrating sphere. The external QY as a function of excitation wavelength for the Li2B4O7:Sm and Li2B4O7:Sm, Ag glasses are presented in Fig. 11. One can see that absolute QY of the
Fig. 8. The partial energy diagram of Sm3+ ions in the Sm3+-Ag co-doped Li2B4O7 glass showing luminescence mechanism and energy transfer channels. 294
Journal of Luminescence 213 (2019) 290–296
I.I. Kindrat, et al.
Li2B4O7:Sm, Ag glass is promising orange-red luminescent materials. The main priority of the studied glasses is simple preparation technology allowing to produce large luminescent layers of high transparency that is impracticable for powdered and monocrystalline materials. Such UV–visible photo-conversion layers can be used in the Si solar cells working in the regions with intense UV-radiation including outer space [11]. Thus, the spectroscopic results, presented in this article, including measurements of external QY of the Sm3+ luminescence, can significant extend the application of glasses co-doped with Sm3+ and Ag. 4. Conclusions The lithium tetraborate (Li2B4O7) glasses, doped with Sm3+ and codoped with Sm3+ and Ag have been obtained and studied in detail by conventional EPR and optical spectroscopy methods. On the basis of analysis of obtained results, it is possible to summarise the following:
• The Sm dopant is incorporated into the structure of lithium tetra-
Fig. 11. The dependence of external QY of the Sm3+ luminescence in the Li2B4O7:Sm (a) and Li2B4O7:Sm, Ag (b) glasses as a function of wavelength of photoexcitation.
•
Table 2 External QY of the Sm3+ luminescence in the investigated Li2B4O7:Sm and Li2B4O7:Sm, Ag glasses and some other Sm3+-doped glasses, reported by different authors. Glass composition
QY, %
References
Li2B4O7:Sm Li2B4O7:Sm,Ag CdO–Al2O3–SiO2 Na2O–ZnO–PbO–GeO2–TeO2 Li2O–K2O–BaO–Bi2O3–TeO2 Li2O–Y2O3–Al2O3–SiO2 Li2O–K2O–ZnO–BaO–Sb2O3–B2O3
20.4 29.1 2.52 6.0 7.55 11.58 13.29
this work this work [50] [51] [52] [53] [54]
• • • •
Li2B4O7:Sm, Ag glass upon excitation at 402 nm significantly grows from 20.4% up to 29.1% in comparison with Li2B4O7:Sm glass. Increasing of QY in the Sm3+-Ag co-doped Li2B4O7 glass also is observed under excitations at 475 nm from 12.0% up to 16.6%, 375 nm from 4.2% to 10.2%, and 362 nm from 2.2% to 5.9% (see Fig. 11). The increasing of Sm3+ luminescence QY in the Li2B4O7:Sm, Ag glass in the UV and violet spectral regions is more intense than in the blue and cyan spectral ranges. Strong increasing of absolute QY of Sm3+ luminescence in the Li2B4O7:Sm, Ag glass is associated with transfer of excitation energy from the Ag+ to the Sm3+ centres. The transfer of excitation energy from the Ag+ pair centres and/or ML-Ag nanoclusters to the Sm3+ centres also can be responsible for the Sm3+ luminescence enhancement in the Li2B4O7 glass, co-doped with Sm3+ and Ag. Eventually, effects induced by SPR of the Ag metallic nanoparticles can also lead to increasing of the Sm3+ luminescence intensity. However, in our opinion, mechanism related with plasmonic Ag nanoparticles is insignificant in the investigated Li2B4O7:Sm, Ag glass. Up to present time there are absent articles, which present measurements of external QY of luminescence of the Sm3+ ions in glasses co-doped by Sm3+ and Ag. Recently published articles [17,19–25,27] present increasing of the Sm3+ luminescence intensity in the silver codoped glasses, but have no reported about the QY of luminescence that is essential for applying of luminescent materials in practice. Comparison of the measured luminescence QY with corresponding values, obtained for some other Sm3+-doped glasses, are shown in Table 2. It should be noted that achieved external QY of Sm3+ luminescence in the Sm3+-Ag co-doped Li2B4O7 glass is higher than the QY in other oxide glasses. Hence, it is possible to conclude that the
borate glass exclusively in form of the Sm3+ (4f5, 6H5/2) impurity ions, which reveal typical optical absorption and luminescence spectra. Luminescence emission spectra of the Sm3+ centres in the Li2B4O7 glasses, doped with Sm3+ and co-doped with Sm3+ and Ag show bands belonging to the 4G5/2 → 6HJ (J = 5/2–13/2) 4f – 4f transitions with characteristic decay kinetics. Photoluminescence spectra and decay kinetics of the Ag+ centres and ML-Ag nanoclusters in glass with Li2B4O7:Sm, Ag composition have been registered and analysed. Enhancement of Sm3+ luminescence in the Li2B4O7:Sm, Ag glass was registered as a result of transfer of the excitation energy from the Ag+ centres and the ML-Ag non-plasmonic nanoclusters to the Sm3+. Quantum yield of luminescence of the Sm3+ centres in Li2B4O7:Sm, Ag glass grows from 20.4 to 29.1% as compared with the Li2B4O7:Sm glass. centres The Li2B4O7 glasses co-doped with Sm3+ and Ag are prospective orange-red luminescent materials for different applications, including UV–visible conversion layers.
Acknowledgements This work was partly supported by the Vlokh Institute of Physical Optics (Lviv, Ukraine) in the framework of scientific project No. 0119U100357 of the Ministry of Education and Science of Ukraine. Authors are thankful to M.Sc. I.M. Teslyuk for glasses synthesis and samples preparation. Special thanks to Dr. Y.O. Kulyk from Ivan Franko National University of Lviv (Ukraine) for registration of the XRD patterns. References [1] M. Yamane, Y. Asahara, Glasses for Photonics, Cambridge University Press, 2000, https://doi.org/10.1017/CBO9780511541308. [2] L.D. Pye, V.D. Fréchette, N.J. Kreidl (Eds.), Borate Glasses, Plenum Press, New York, 1978, https://doi.org/10.1007/978-1-4684-3357-9. [3] S. Tanabe, Rare-earth-doped glasses for fiber amplifiers in broadband telecommunication, C.R. Chimie 5 (2002) 815–824 https://doi.org/10.1016/S16310748(02)01449-2. [4] I.I. Kindrat, B.V. Padlyak, A. Drzewiecki, Luminescence properties of the Sm-doped borate glasses, J. Lumin. 166 (2015) 264–275 https://doi.org/10.1016/j.jlumin. 2015.05.051. [5] I.I. Kindrat, B.V. Padlyak, S. Mahlik, B. Kukliński, Y.O. Kulyk, Spectroscopic properties of the Ce-doped borate glasses, Opt. Mater. 59 (2016) 20–27 https://doi.org/ 10.1016/j.optmat.2016.03.053. [6] I.I. Kindrat, B.V. Padlyak, Luminescence properties and quantum efficiency of the Eu-doped borate glasses, Opt. Mater. 77 (2018) 93–103 https://doi.org/10.1016/j. optmat.2018.01.019. [7] G. Blasse, B.C. Grabmaier, Luminescent Materials, Springer Verlag, Berlin, 1994https://doi.org/10.1007/978-3-642-79017-1.
295
Journal of Luminescence 213 (2019) 290–296
I.I. Kindrat, et al.
[32] B.V. Padlyak, W. Ryba-Romanowski, R. Lisiecki, V.T. Adamiv, Ya.V. Burak, I.M. Teslyuk, Synthesis, EPR and optical spectroscopy of the Cr-doped tetraborate glasses, Opt. Mater. 34 (2012) 2112–2119 https://doi.org/10.1016/j.optmat.2012. 06.014. [33] B.V. Padlyak, A. Drzewiecki, Spectroscopy of the CaB4O7 and LiCaBO3 glasses, doped with terbium and dysprosium, J. Non-Cryst. Solids 367 (2013) 58–69 https://doi.org/10.1016/j.jnoncrysol.2013.02.018. [34] G.H. Dieke, H.M. Crosswhite, The spectra of the doubly and triply ionized rare earths, Appl. Opt. 2 (1963) 675–686 https://doi.org/10.1364/AO.2.000675. [35] W.T. Carnall, P.R. Fields, K. Rajnak, Electronic energy levels in the trivalent lanthanide aquo ions. I. Pr3+, Nd3+, Pm3+, Sm3+, Dy3+, Ho3+, Er3+, and Tm3+, J. Chem. Phys. 49 (1968) 4424–4442 https://doi.org/10.1063/1.1669893. [36] B.V. Padlyak, A. Drzewiecki, T.B. Padlyak, V.T. Adamiv, I.M. Teslyuk, Resonant excited UV luminescence of the Gd3+ centres in borate glasses, co-doped with Gd and Ag, Opt. Mater. 79 (2018) 302–309 https://doi.org/10.1016/j.optmat.2018.03. 050. [37] I.I. Kindrat, B.V. Padlyak, B. Kukliński, A. Drzewiecki, V.T. Adamiv, Enhancement of the Eu3+ luminescence in Li2B4O7 glasses co-doped with Eu and Ag, J. Lumin. 204 (2018) 122–129 https://doi.org/10.1016/j.jlumin.2018.07.051. [38] I.I. Kindrat, B.V. Padlyak, R. Lisiecki, V.T. Adamiv, I.M. Teslyuk, Enhancement of the Er3+ luminescence in Er–Ag co-doped Li2B4O7 glasses, Opt. Mater. 85 (2018) 238–245 https://doi.org/10.1016/j.optmat.2018.08.052. [39] A.S. Kuznetsov, V.K. Tikhomirov, M.V. Shestakov, V.V. Moshchalkov, Ag nanocluster functionalized glasses for efficient photonic conversion in light sources, solar cells and flexible screen monitors, Nanoscale 5 (2013) 10065–10075 https:// doi.org/10.1039/c3nr02798h. [40] A. Meijerink, M.M.E. van Heek, G. Blasse, Luminescence of Ag+ in crystalline and glassy SrB4O7, J. Phys. Chem. Solids 54 (1993) 901–906 https://doi.org/10.1016/ 0022-3697(93)90216-E. [41] H. Guo, X.F. Wang, J.D. Chen, F. Li, Ultraviolet light induced white light emission in Ag and Eu3+ co-doped oxyfluoride glasses, Optic Express 18 (2010) 18900–18905 https://doi.org/10.1364/OE.18.018900. [42] H. Zhong, B. Chen, S. Fu, X. Li, J. Zhang, S. Xu, Y. Zhang, L. Tong, G. Sui, H. Xia, Broadband emission and flat optical gain glass containing Ag aggregates for tunable laser, J. Am. Ceram. Soc. 102 (2019) 1150–1156 https://doi.org/10.1111/jace. 16006. [43] X. Li, H. Zhong, B. Chen, G. Sui, J. Sun, S. Xu, L. Cheng, J. Zhang, Highly stable and tunable white luminescence from Ag-Eu3+ co-doped fluoroborate glass phosphors combined with violet LED, Optic Express 26 (2018) 1870–1881 https://doi.org/10. 1364/OE.26.001870. [44] H. Fares, T. Castro, J.R. Orives, D.F. Franco, M. Nalin, White light and multicolor emission tuning in Ag nanocluster doped fluorophosphate glasses, RSC Adv. 7 (2017) 44356–44365 https://doi.org/10.1039/C7RA08778K. [45] H. Fares, S.N.C. Santos, M.V. Santos, D.F. Franco, A.E. Souza, D. Manzani, C.R. Mendonça, M. Nalin, Highly luminescent silver nanocluster-doped fluorophosphate glasses for microfabrication of 3D waveguides, RSC Adv. 7 (2017) 55935–55944 https://doi.org/10.1039/C7RA11792B. [46] Y. Petit, C.-H. Park, J.-M. Mok, E. Smetanina, B. Chimier, G. Duchateau, T. Cardinal, L. Canioni, S.-H. Park, Ultrashort laser induced spatial redistribution of silver species and nano-patterning of etching selectivity in silver-containing glasses, Optic Express 27 (2019) 13765 13680 https://doi.org/10.1364/OE.27.013675. [47] I.I. Kindrat, B.V. Padlyak, A. Drzewiecki, Intrinsic luminescence of un-doped borate glasses, J. Lumin. 187 (2017) 546–554 https://doi.org/10.1016/j.jlumin.2017.03. 071. [48] R.F. Wei, J.J. Li, J.Y. Gao, H. Guo, Enhancement of Eu3+ luminescence by Ag species (Ag NPs, ML-Ag, Ag+) in oxyfluoride glasses, J. Am. Ceram. Soc. 95 (2012) 3380–3382 https://doi.org/10.1111/j.1551-2916.2012.05459.x. [49] R. Ma, J. Gao, Q. Xu, S. Cui, X. Qiao, J. Du, X. Fan, Eu2+ promoted formation of molecule-like Ag and enhanced white luminescence of Ag/Eu-codoped oxyfluoride glasses, J. Non-Cryst. Solids 432 (2016) 348–353 https://doi.org/10.1016/j. jnoncrysol.2015.10.032. [50] Y. Lei, F.F. Fu, L. Zheng, Z.Q. Wang, X. Zhao, H. Lin, Absolute luminous flux and quantum yield of Sm3+-doped cadmium-aluminum-silicate glasses under the pumping of blue light emitting diode, Appl. Mech. Mater. 275–277 (2013) 1974–1977 https://doi.org/10.4028/www.scientific.net/AMM.275-277.1974. [51] F. Wang, B.J. Chen, H. Lin, E.Y.B. Pun, Spectroscopic properties and external quantum yield of Sm3+ doped germanotellurite glasses, J. Quant. Spectrosc. Radiat. Transfer 147 (2014) 63–70 https://doi.org/10.1016/j.jqsrt.2014.05.014. [52] H. Lin, X.Y. Wang, C.M. Li, X.J. Li, S. Tanabe, J.Y. Yu, Spectral power distribution and quantum yields of Sm3+-doped heavy metal tellurite glass under the pumping of blue lighting emitting diode, Spectrochim. Acta A 67 (2007) 1417–1420 https:// doi.org/10.1016/j.saa.2006.10.039. [53] F. Fu, B. Chen, L. Shen, E.Y.B. Pun, H. Lin, Multi-channel transition emissions of Sm3+ in lithium yttrium aluminum silicate glasses and derived opalescent glass ceramics, J. Alloy. Comp. 582 (2014) 265–272 https://doi.org/10.1016/j.jallcom. 2013.08.040. [54] L.F. Shen, B.J. Chen, E.Y.B. Pun, H. Lin, Sm3+-doped alkaline earth borate glasses as UV → visible photon conversion layer for solar cells, J. Lumin. 160 (2015) 138–144 https://doi.org/10.1016/j.jlumin.2014.11.052.
[8] W.M. Yen, Sh. Shionoya, H. Yamamoto (Eds.), Phosphor Handbook, CRC Press, Boca Raton, 2007, https://doi.org/10.1201/9781420005233. [9] C.K. Jayasankar, P. Babu, Optical properties of Sm ions in lithium borate and lithium fluoroborate glasses, J. Alloy. Comp. 307 (2000) 82–95 https://doi.org/10. 1016/S0925-8388(00)00888-4. [10] P. Kaur, S. Kaur, G.P. Singh, D.P. Singh, Sm3+ doped lithium aluminoborate glasses for orange coloured visible laser host material, Solid State Commun. 171 (2013) 22–25 https://doi.org/10.1016/j.ssc.2013.07.021. [11] I.I. Kindrat, B.V. Padlyak, R. Lisiecki, Judd–Ofelt analysis and radiative properties of the Sm3+ centres in Li2B4O7, CaB4O7, and LiCaBO3 glasses, Opt. Mater. 49 (2015) 241–248 https://doi.org/10.1016/j.optmat.2015.09.024. [12] B.V. Padlyak, I.I. Kindrat, R. Lisiecki, V.T. Adamiv, I.M. Teslyuk, New effective luminescent materials based on the Sm-doped borate glasses, Adv. Mater. Lett. 8 (2017) 723–734 https://doi.org/10.5185/amlett.2017.1436. [13] C. Jiang, Y. Huang, S. Park, K. Jang, H.J. Seo, Luminescence and spectral hole burning of Sm2+ doped in Li2O–SrO–B2O3 glass-ceramics, Spectrochim. Acta A 72 (2009) 412–416 https://doi.org/10.1016/j.saa.2008.10.014. [14] H. Song, M. Nogami, Room-temperature hole-burning and sublinear hole-growth dynamics in an Sm2+-doped aluminosilicate glass, J. Non-Cryst. Solids 297 (2002) 113–119 https://doi.org/10.1016/S0022-3093(01)01035-3. [15] V.C. Costa, Y. Shen, A.M.M. Santos, K.L. Bray, Luminescence measurements on Sm2+-doped sol–gel glasses, J. Non-Cryst. Solids 304 (2002) 238–243 https://doi. org/10.1016/S0022-3093(02)01029-3. [16] O.L. Malta, P.A. Santa-Cruz, G.F. De Sá, F. Auzel, Fluorescence enhancement induced by the presence of small silver particles in Eu3+ doped materials, J. Lumin. 33 (1985) 261–272 https://doi.org/10.1016/0022-2313(85)90003-1. [17] J.A. Jiménez, S. Lysenko, H. Liu, M. Sendova, Luminescence of trivalent samarium ions in silver and tin co-doped aluminophosphate glass, Opt. Mater. 33 (2011) 1215–1220 https://doi.org/10.1016/j.optmat.2011.02.013. [18] M. Eichelbaum, K. Rademann, Plasmonic enhancement or energy transfer? On the luminescence of gold-, silver-, and lanthanide-doped silicate glasses and its potential for light-emitting devices, Adv. Funct. Mater. 19 (2009) 2045–2052 https://doi. org/10.1002/adfm.200801892. [19] M.R. Dousti, Plasmonic effect of silver nanoparticles on the upconversion emissions of Sm3+-doped sodium-borosilicate glass, Measurement 56 (2014) 117–120 https://doi.org/10.1016/j.measurement.2014.06.024. [20] I. Mechergui, H. Fares, S.A. Mohamed, M. Nalin, H. Elhouichet, Coupling between surface plasmon resonance and Sm3+ ions induced enhancement of luminescence properties in fluoro-tellurite glasses, J. Lumin. 190 (2017) 518–524 https://doi. org/10.1016/j.jlumin.2017.06.013. [21] S.Q. Mawlud, A comparative enhancement of Au and Ag NPs role on radiative properties in Sm3+ doped zinc-sodium tellurite glass: Judd-Ofelt parameter, Spectrochim. Acta A 209 (2019) 78–84 https://doi.org/10.1016/j.saa.2018.10.032. [22] G.E. Malashkevich, A.V. Semchenko, A.A. Sukhodola, A.P. Stupak, A.V. Sukhodolov, B.V. Plyushch, V.V. Sidskiĭ, G.A. Denisenko, Influence of silver on the Sm3+ luminescence in “Aerosil” silica glasses, Phys. Solid State 50 (2008) 1464–1472 https://doi.org/10.1134/S1063783408080131. [23] L. Li, Y. Yang, D. Zhou, Z. Yang, X. Xu, J. Qiu, Investigation of the role of silver species on spectroscopic features of Sm3+-activated sodium–aluminosilicate glasses via Ag+-Na+ ion exchange, J. Appl. Phys. 113 (2013) 193103https://doi.org/10. 1063/1.4807313. [24] J.J. Li, R.F. Wei, X.Y. Liu, H. Guo, Enhanced luminescence via energy transfer from Ag+ to RE ions (Dy3+, Sm3+, Tb3+) in glasses, Optic Express 20 (2012) 10122–10127 https://doi.org/10.1364/OE.20.010122. [25] S. Thomas, M.S. Sajna, Sk.N. Rasool, M. Gopinath, C. Joseph, N.V. Unnikrishnan, Sm3+-doped fluorophosphate glass: formation of Ag nanoparticles via Ag+/K+ ion exchange and their effects on optical and dielectric properties, Opt. Mater. 39 (2015) 167–172 https://doi.org/10.1016/j.optmat.2014.11.019. [26] M. Dyrba, P.-T. Miclea, S. Schweizer, Surface plasmons for fluorescence enhancement in Sm-doped borate glasses, Radiat. Meas. 45 (2010) 314–316 https://doi. org/10.1016/j.radmeas.2010.01.028. [27] Y. Gao, S. Murai, K. Fujita, K. Tanaka, Visible and near-infrared photoluminescence enhanced by Ag nanoparticles in Sm3+-doped aluminoborate glass, Opt. Mater. 86 (2018) 611–616 https://doi.org/10.1016/j.optmat.2018.10.018. [28] B.V. Padlyak, S.I. Mudry, Y.O. Kulyk, A. Drzewiecki, V.T. Adamiv, Y.V. Burak, I.M. Teslyuk, Synthesis and X-ray structural investigation of undoped borate glasses, Mater. Sci. Pol. 30 (2012) 264–273 https://doi.org/10.2478/s13536-012-0032-1. [29] A.T. Brant, B.E. Kananan, M.K. Murari, J.W. McClory, J.C. Petrosky, V.T. Adamiv, Ya.V. Burak, P.A. Dowben, L.E. Halliburton, Electron and hole traps in Ag-doped lithium tetraborate (Li2B4O7) crystals, J. Appl. Phys. 110 (2011) 093719https://doi. org/10.1063/1.3658264. [30] A.T. Brant, D.A. Buchanan, J.W. McClory, V.T. Adamiv, Ya.V. Burak, L.E. Halliburton, N.C. Giles, Photoluminescence from Ag2+ ions in lithium tetraborate (Li2B4O7) crystals, J. Lumin. 153 (2014) 79–84 https://doi.org/10.1016/j. jlumin.2014.03.008. [31] B.E. Kananen, E.S. Maniego, E.M. Golden, N.C. Giles, J.W. McClory, V.T. Adamiv, Ya.V. Burak, L.E. Halliburton, Optically stimulated luminescence (OSL) from Agdoped Li2B4O7 crystals, J. Lumin. 177 (2016) 190–196 https://doi.org/10.1016/j. jlumin.2016.04.032.
296