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Spectroscopic properties of Sm3+ and V4+ ions in Na2O–SiO2–ZrO2 glasses
Journal of Molecular Structure 1054–1055 (2013) 339–348
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Spectroscopic properties of Sm3+ and V4+ ions in Na2O–SiO2–ZrO2 glasses K. Neeraja, T.G.V.M. Rao, A. Rupesh Kumar, V. Uma Lakshmi, N. Veeraiah, M. Rami Reddy ⇑ Department of Physics, Acharya Nagarjuna University, Nagarjuna Nagar 522 510, India
h i g h l i g h t s XRD techniques are indicates that the glasses have amorphous nature. 4+
ESR spectrum indicates the vanadyl ions can exists in V
state. 3+
J–O parameters are indicates the strong electrostatic field exists around Sm
a r t i c l e
i n f o
Article history: Received 26 June 2013 Received in revised form 23 September 2013 Accepted 23 September 2013 Available online 30 September 2013 Keywords: XRD EDS Infrared (FT-IR) Raman EPR Optical absorption and luminescence spectra
ions.
a b s t r a c t Na2O–SiO2–ZrO2 glasses of Sm3+ ions with and without V2O5 are characterized by spectroscopic and optical properties. The XRD and EDS spectra of the glass samples reveal an amorphous nature with different compositions within the glass matrix. The Infrared and Raman spectral studies are carried out and the existence of conventional structural units are analyzed in the glass network. The ESR spectra of the glass samples have indicating that a considerable proportion of vanadium ion exists in V4+ state. The optical absorption spectra of these glasses are recorded at room temperature, from the measured intensities of various absorption bands the Judd–Ofelt parameters X2, X4 and X6 are calculated. The photo-luminescence spectra recorded with excited wavelength 400 nm, five emission bands are observed; in this the energy transfer probability takes place between Sm3+ and V4+ ions. Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction The study of oxide glasses with rare earth ion is of great importance due to the wide range of applications in sensiting solid state and glass lasers, optical fiber and optical detectors for fluorescent display devices. Due to these optical properties Sm3+ ions in the glass network may change the chemical environment. They have high emissions efficiency to recognize the spectral properties helpful to design of new glass composition for photonic materials [1– 5]. The presence of alkali oxides like sodium act like a network modifier in the glass network enhancing the rare earth suitability of the glasses to produce non-bridging oxygen atoms (NBO) that helps in the design of high efficiency in short length fiber amplifiers [6–9]. Silicate, known as a glass forming oxide enters into alkali metal oxide in glass matrix eventually changes the glass network leading to the formation of non-bridging oxygen atoms. Silicate has its applications in different areas of electronics and other fields due to high chemical resistance, coefficient of thermal expansion and good UV transparency [10–12]. ⇑ Corresponding author. Tel.: +91 9866804948; fax: +91 8632293378. E-mail address: [email protected] (M. Rami Reddy). 0022-2860/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.molstruc.2013.09.038
Zirconium oxide is one of the intermediate oxides that enters the sodium silicate glasses and improves the transparency, electrical resistivity, chemical inertness. This results in hike of the refractive index, decreases in the cutoff wavelength and reduction photochromism of the glasses and helps to improve the optical and mechanical properties [13–17]. Vanadium is one the transition metal oxide that displays excellent properties of electrochromisim of blue M green M yellow and has unique properties because of its semiconducting properties that is the result of electron hopping between the ions. Vanadium exists in three possible oxidation states i.e. V3+, V4+ and V5+. The V2O5 can be incorporated in the rare earth glasses it undergoes radiative and non-radiative transitions are takes place with in glass matrix. Due to this the energy transfer process increases the laser efficiency of the glasses and also has significant applications in research and development of new laser materials [18–25]. Keeping in view of the above interesting results, the present work makes a quantitative evaluation of the radiative and non-radiative energy transfer in the Sm2O3:V2O5 codoped sodium silicon zirconium (NSZ) glasses are used for the present study. In the present study the spectroscopic characteristics of Sm3+ ions and the energy transfer probability in (Sm3+:V4+) co doped NSZ
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glasses is monitored, investigating the structural changes that takes place due to oxidation state of vanadium. The shifting role of modifier ions varied in the spectroscopic and optical properties of Sm2O3 ions in Na2O–SiO2–ZrO2 glasses co doped with V2O5 using XRD, EDS, EPR, FT-IR, Raman spectra, Optical Absorption and Luminescence studies are recorded. 2. Experimental technique Analytical reagents with 99.9% purity of Na2CO3, SiO2, ZrO2, Sm2O3 and V2O5 are used to prepare the glasses. Here samarium and vanadium are employed as dopants in the glass network. Glasses were prepared by using melt quenching technique; in this calculated quantities of chemicals in mol% were taken in an agate mortar and then powdered to obtain homogeneous mixture. The mixture is taken in silica crucible and heated for about 1 h in an automatic temperature controlled furnace at a temperature range 1350–1450 °C. The melt is quickly poured into preheated brass mould so as to obtain the required shape. The obtained samples were immediately transferred to the muffle furnace of 450 °C temperature for annealing. The muffle furnace containing samples was switched off immediately and left to cool at room temperature at a rate of 25 °C/h to avoid thermal stress and to get the structural stability. Later the samples were polished to final dimensions of 1 cm 1 cm 0.2 cm. The glass samples are transparent and appear to have good optical quality. The composition of the prepared glasses containing variable amount of contents are given in Table 1. Density of the glasses was determined to an accuracy of (±0.0001) by the standard Archimedes Principle using o-xylene (99.9% pure) as buoyant liquid and the refractive index of the glass sample is measured by using Abbe’s refractrometer. The X-ray diffraction spectrum is recorded on a diffractometer with copper target (XRDARLX’TRA) and nickel filter operated at 40KV, 30 mA. The Energy Dispersive Spectroscopy measurements were conducted on a Thermo Instruments Model Noran System 6 attached to scanning electron microscope. The electron spin resonance (ESR) spectra of the fine powder of the sample were recorded at room temperature. Infrared Transmission Spectra are recorded on a JASCO-FT-IR -53000 spectrophotometer with resolution of 0.1 cm1 in the spectral range 400–4000 cm1 using KBr pellets (300 mg) containing the pulverized sample (1.5 mg). The Raman Spectra (model Nexus 670 Nicolet – Madison – WI, USA) is recorded on Fourier transform Raman spectrometer with resolution of 4 cm1 in the 400–1500 cm1. The optical absorption (UV–Vis) Spectra are recorded on JASCO, V-570 Spectrophotometer from 200 to 1800 nm with Spectral resolution of 0.1 nm. The luminescence Spectra are recorded at room temperature on a photon Technology International (PTI) spectroflurometer with excited wavelength 400 nm from 300 to 1200 nm. 3. Results 3.1. Physical properties To understand the physical properties of the glasses, various parameters are calculated, i.e. practically measured density (d)
and refractive index (The error in density measurements and refractive indices are estimated to be ±0.004 g/cm3 and ±0.0001 respectively) are calculated. Along with this function, some other physical parameters also calculated [26–29] using conventional formulae such as vanadium ion concentration (Ni), mean ionic separation (ri), polaron radius (rp), field strength (Fi), electronic polaraizability (a), reflection loss, Molar refractivity (RM) and optical dielectric constant (e) which are presented in the Table 2. Fig. 1 shows the variation of density and refractive index as a function of glass samples. Fig. 2 represents the ionic concentration and electronic polaraizability as a function of x mol% (x = 0.2, 0.4, 0.6, 0.8, 1.0) of dopant. 3.2. X-ray diffraction spectra The amorphous nature of the Sm3+:V4+ co-doped NSZ glasses was confirmed by X-ray diffraction spectra, which Shows a broad bump around the centered 27° (=2h). There are no observed sharp lines which shows that all the prepared samples confirms the amorphous nature and it is shown in Fig. 3. 3.3. Energy Dispersive Spectroscopy From the Energy Dispersive Spectroscopy (EDS), the chemical compositions of the glasses were determined as shown in Fig. 4. The inset figure shows the electronic image spectrum of the glass sample of 1 mol% V2O5. The analysis indicates the presence of sodium (Na), silicon (Si), zirconium (Zr), samarium(Sm), oxygen (O), carbon (C), and vanadium (V) elements in the glass network. 3.4. Fourier transforms Infrared transmission spectra (FT-IR) The Fourier transforms Infrared transmission spectra gives information about the various vibrational modes and also provides structural information of the glass network. The spectra of undoped and doped Sm3+:V4+ codoped NSZ glasses are shown in Fig. 5. The spectral features are analyzed from the studied glasses show the vibration bands without any obvious variations. The observed IR spectral bands are given in Table 3. The spectra exhibit a series of bands [30] one at about 470 cm1, the second band at around 640–660 cm1 and the third at around 730–760 cm1. Two bands are located at around 800–900 cm1 and one sharp band with a peak is located at about 960–970 cm1. Another belonging to the OH groups is found around 1500–1700 cm1 [31]. 3.5. Raman spectra Raman spectra are used to characterize the local arrangement of the structure of the glasses and also give information about the structural properties that would support the Infrared transmission spectra. Fig. 6 represents the Raman spectra of the undoped and doped Sm3+:V2O5 NSZ glasses. The Raman spectra of the glasses and band positions are presented in Table 4. The spectra of NSZ glasses have revealed a peak at round 350–365 cm1 and structural vibrations are observed at around 800 cm1. In the spectrum
Table 1 Composition of the studied glasses (batch mol%). S. no.
Glass
Na2O (mol%)
SiO2 (mol%)
ZrO2 (mol%)
Sm2O3 (mol%)
V2O5 (mol%)
1 2 3 4 5 6 7
Pure Smv0 Smv1 Smv2 Smv3 Smv4 Smv5
40 40 40 40 40 40 40
55 54 54 54 54 54 54
5 5 4.8 4.6 4.4 4.2 4
– 1 1 1 1 1 1
– – 0.2 0.4 0.6 0.8 1.0
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K. Neeraja et al. / Journal of Molecular Structure 1054–1055 (2013) 339–348 Table 2 Various physical properties of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses. Physical Parameters 3
Density d (g/cm ) (±0.004) Average molecular weight (M) Ion concentration Ni (1020 ions/cm3) (±0.005) Interionic distance ri (Å) (±0.005) Polaron radius rp (Å) (±0.005) Field strength Fi (1015 cm2) (±0.005) Refractive index n (±0.0001) Reflection loss Molar reflectivity RM (cm3) (±0.005) Electronic polaraizability (ae) (1022 ions/cm3) (±0.005) Optical dielectric constant (e0) (±0.005)
Pure
Smv0
Smv1
Smv2
Smv3
Smv4
Smv5
2.679 63.99 – – – – 1.674 0.033 8.969 – 2.803
2.692 66.88 – – – – 1.662 0.032 9.197 – 2.763
2.718 67.00 0.488 27.35 11.02 2.47 1.663 0.032 9.131 18.106 2.765
2.780 66.71 1.004 21.51 8.66 3.99 1.665 0.032 8.909 8.832 2.772
2.785 66.63 1.510 18.77 7.56 5.24 1.667 0.033 8.904 5.885 2.778
2.769 66.55 2.005 17.08 6.88 6.33 1.666 0.033 8.940 4.431 2.777
2.762 66.46 2.502 15.86 6.39 7.33 1.667 0.033 8.957 3.552 2.778
Fig. 3. XRD spectra of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses.
Fig. 1. Variation of density and refractive index with glass sample of Na2O–SiO2– ZrO2: Sm3+:V4+ codoped glasses.
Fig. 4. EDS spectra of 1 mol% V2O5 in Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses.
the nature of its bonding with the nearest neighboring ligands. The EPR spectra recorded at room temperature for the present investigated NSZ: Sm3+:V4+ co-doped glasses. No signals are observed for the undoped glasses. When V2O5 are introduced into the glass matrix, the EPR resonance spectra exhibit eight parallel and eight perpendicular lines arising from the unpaired 3d1 electron of VO2+ ions with 51V (I = 7/2) isotope in an axially symmetric field. The axial spin-Hamiltonian for hyperfine interaction is used to describe the spectra of V4+ ions [35]. Fig. 2. Variation of ionic concentration and electronic polaraizability of Na2O–SiO2– ZrO2: Sm3+:V4+ codoped glasses.
contains V2O5, stretching vibrations are observed at around 600 cm1 and another two band is observed at 900 cm1 and 1070 cm1 [32–34].
3.6. Electron paramagnetic resonance spectra Electron paramagnetic resonance spectra is a method to understand the symmetry of surroundings of the paramagnetic ion and
H ¼ b½g jj Bz Sz þ g ? ðBx Sx þ By SyÞ þ Ajj Sz Iz þ A? ðSx Ix þ Sy Iy Þ
ð4Þ
Here b denotes Bohr magneton, g||, g\ and A||, A\ denotes the components of the hyperfine coupling tensor, Bx, By and Bz denotes components of the magnetic field, Sx, Sy, Sz and Ix, Iy, Iz are the spin operator of the electron and the nucleus. The magnetic field positions for the parallel and perpendicular hyperfine peaks are based on the second order perturbation terms are
"
# A2? 63 m2 Bjj ðmÞ ¼ Bjj ð0Þ mAjj 4 1Bjj ð0Þ
ð5Þ
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Fig. 6. Raman spectra of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses.
Fig. 5. FT-IR spectra of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses.
2 3 2 A2jj þ A? 5 63 m2 B? ðmÞ ¼ B? ð0Þ mA? 4 4 4B? ð0Þ
e2 p ¼ ð6Þ
From the above equation m refer to the nuclear spin magnetic quantum number, bearing values ±7/2, ±5/2, ±1/2; B|| (0) = h/g||b and B\(0) = h/g\b. From the above parameters, the dipolar hyper fine coupling parameters P = 2dbbN r3 and the Fermi contact interaction (K), are evaluated [36] using the expression
Ajj ¼ P½ð4=7Þ-K þ ðg jj g e Þ þ ð3=7Þðg ? g e Þ
ð7Þ
A? ¼ P½ð2=7Þ-K þ ð11=14Þðg ? g e Þ
ð8Þ
In the equation, ge = 2.0023 and refer to the g factor of the free electron. The term P and K in the above equation result from the S-character of the magnetic spin of the vanadium. Generally the S-character is due to the partial unpairing or polarization of the inner s-electron gives the interaction with the unpaired d electrons. The values Dg||/Dg\ are also calculated for the tetragonality of the vanadium site. The molecular bonding coefficient b2 and e2 p are evaluated by correlating the EPR and optical data using [37] the given expressions
b2 ¼
ðg e g jj ÞDjj 8k
ð9Þ
ðg e g ? ÞD? 8k
ð10Þ
In the above equation, k is the free-ion value of spin orbit coupling constants for the vo2+ ions and is taken as 170 cm1. D|| and D\ are energies of the electronic transitions from 2B2 ? 2Bg and 2 B2 ? 2Eg respectively. The above evaluated values from these spectra along with the other pertinent data are furnished in Table 5. 3.7. Optical absorption spectra The absorption spectra of Sm3+:V4+ ions codoped NSZ glasses show a large number of bands; the observed bands are assigned on the basis of the reported energy levels [38–41] of Sm3+ ions of different glass hosts. With the addition of V2O5, the absorption intensity enhances and exhibit more absorption band. The bands are observed at 402, 470, 1070, 1221, 1260, 1360, 1370, 1465, 1522 nm [42,43] these bands are related to samarium (Sm3+) ions resulting due to the different transitions are from 6H5/2 ? 6P3/2, 4 I13/2 + 4I11/2 + 4M15/2, 6F9/2, 6F7/2, 6F5/2, 6F3/2, 6F1/2, 6H15/2. When V2O5 is added to the glass network two more additional bands are observed at 683 and 1070 nm due to the transitions 2 B2 ? 2Bg and 2B2 ? 2Eg. Thus, from these optical absorption spectra totally nine bands are observed for Sm3+:V4+ doped NSZ glasses as shows in Fig. 7. from the observed edge, we have evaluated the
Table 3 The FT-IR band positions of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses. Glass samples
Band assignments
Pure
Smv0
Smv1
Smv2
Smv3
Smv4
Smv5
470 – 732 – 890 961 1517 1695
471 – 742 – 884 968 1522 1695
470 648 743 836 884 964 1527 1696
470 653 743 818 883 963 1522 1695
471 653 742 816 884 965 1522 1695
470 652 743 816 888 963 1524 1696
471 653 743 818 889 965 1524 1696
Bending and rocking motion of Si–O–Si V–O–V bending vibrations Zr–O–Zr/ZrO4 structural units V–O–V chains Si–O–Si symmetric stretching vibrations Si–O–Zr units Stretching mode of Si–OH Water molecular vibrations
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K. Neeraja et al. / Journal of Molecular Structure 1054–1055 (2013) 339–348 Table 4 Raman band positions of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses. Glass samples
Band assignments
Pure
Smv0
Smv1
Smv2
Smv3
Smv4
Smv5
353 – 856 949 1090
353 – 854 947 1091
355 617 854 947 1091
357 617 852 949 1092
361 615 853 949 1091
361 612 856 947 1092
361 612 856 947 1091
Si–O–Si rocking vibrations V–O–V vibrations/combinations of various vibrations Si–O–Si bending vibrations Si–O–Zr rocking vibrations Si–O–Si stretching vibrations
Table 5 The spin-Hamiltonian parameters and molecular orbitals coefficients for Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses. Glass code g|| ||
g\
A||
Smv0 Smv1 Smv2 Smv3 Smv4
1.9085 1.9191 1.9191 1.9191 1.9186
183 181 181 181 181
1.8926 1.8967 1.8967 1.8968 1.8966
||
104 cm1 A\ 104 cm1 b⁄2 67 66 66 66 66
0.0471 0.0417 0.0417 0.0417 0.0420
e2 p
g||||
g\
g||
||/g\
0.0863 0.0830 0.0830 0.0830 0.0831
0.0938 0.0832 0.0832 0.0832 0.0837
0.1097 0.1056 0.1056 0.1055 0.1057
0.8550 0.7878 0.7878 0.7886 0.7918
P 104 cm1 K 144.5 140.4 140.4 140.2 140.2
0.8355 0.8476 0.8476 0.8478 0.8479
AIjj
jj
104 cm1 AI? 104 cm1
62.28 62 62 62.2 62.2
53 53 53 52.8 52.8
Fig. 7. Optical absorption spectra of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses.
optical band gap (Eo) of these glasses by drawing Tauc plot between (ahm)1/2, (ahm)2 as a function of hm as per the given equation
aðmÞhm ¼ Cðhm Eo Þn
ð1Þ
Here C is a constant and the exponent (n) can take values 1/2 and 2 for indirect, direct transitions in glasses respectively [44]. Tauc plots for direct transition in Fig. 8(a) and indirect transition are shown in Fig. 8(b). Extrapolating the linear portion of these plots as (ahm)1/ 2 = 0, (ahm)2 = 0 gives optical band gap, along with the theoretical optical band gap energy also calculated using equation E = hc/k. Here h is the plank’s constant, c is the velocity of light and k cutoff wavelength respectively. The value of DE is calculate by taking the reciprocal of the slope of the linear portion in the lower photon energy region of ln(a) verses hm plot are shown in Fig. 9. Urbach energy which corresponds to the width of localized states and characterizes the degree of disorder in the glass systems. The value of DE in the present work lies in the range 0.25–0.27 eV for all the glasses. The increase in Urbach energy with increasing the concentration of V2O5. In addition to this, the theoretical optical basicity (Kth) of the glasses can be calculated for the Sm3+:V2O5 doped NSZ glasses [45,46] by using the formula
Fig. 8. Tauc plots to evaluate (a) direct band gap, (b) in-direct band gap of Na2O– SiO2–ZrO2: Sm3+:V4+ codoped glasses.
Kth ¼
n X Zi ri i¼1
Zdi
ð2Þ
where n denotes the total number of cations present, Zi denotes the oxidation number of the ith cation, ri denotes the ratio of the
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Fig. 9. A plots of ln(a) and hm for Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses.
number of the ith cation to the number of oxides present and di denote basicity moderating parameters of ith cation. The basicity moderating parameter is calculated from the following equation
di ¼ 1:36ðxi 0:26Þ
Fig. 10. Luminescence spectra of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses.
ð3Þ
where xi represents the pouling electro negativity of the cation. The theoretical and evaluated values of cutoff wavelength, theoretical band gap, direct and indirect band gap and the theoretical optical basicity (Kth) are presented in Table 6. 3.8. Photoluminescence spectra The Photoluminescence spectra of Sm3+:V4+ doped NSZ glasses are recorded at room temperature with excited wavelength 400 nm in region 450–900 nm. When Sm3+ ions are excited at 6 P3/2 level (402 nm), the initial population relaxes finally to the 4 G5/2 level. Between 6P3/2 and 4G5/2 levels, there are several intermediate levels with smaller energy difference, which encourage their efficient non-radiative relaxation there by leading to the population at the 4G5/2 state. This state is distinct from the intermediate lower state i.e. 6F11/2. It could be stated that radiative transitions and relaxations by non-radiative energy transfer are the two main processes, which could finally depopulate the 4G5/2 state. The emission spectra of the NSZ glasses containing Sm3+ ions exhibit four emission transitions, which are assigned to 4 G5/2 ? 6F5/2 (576 nm), 4G5/2 ? 6F7/2 (604 nm), 4G5/2 ? 6F9/2 (648 nm) and 4G5/2 ? 6F11/2 (708 nm) [47,48]. By the addition of V2O5 another band is observed at round 782 nm with the transition 2 E ? 2T2 [49,50]. The Fig. 10 shows the luminescence spectra of Sm3+:V4+ codoped NSZ glasses. 4. Discussions Among the physical properties, density is an effective tool to explore the degree of structural compactness of the glasses. In the present work, increase in density is observed with the increasing content of V2O5 in all the glasses. Basically, when V2O5 enters into
Fig. 11. EPR spectra of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses.
the glass network in two forms, they acts as network modifier at low content and at high content it acts as network forming group. Due to this, non-bridging oxygen content is further increases. The density and refractive index of the observed parameters vary nonlinearly with increasing vanadium concentration. From these observations, the effect of V2O5 in ionic concentration and electronic polaraizability of Sm3+:V2O5 NSZ glasses vary non-linearly. It is observed that both the parameters tend to be inversely proportional to the increase in x mol% of vanadium concentration. The polaraizability is high at x = 1 mol%, whereas, its ionic concentration lower due to feeble ionic mobility and increase in interionic separation (ri) is observed. An eventual decrease in interionic
Table 6 The cutoff wavelength, optical band gaps, Urbach energy and optical Basicity of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses. Glass samples
Cutoff wavelength
Theoretical band gap
Direct band gap (eV)
Indirect band gap (eV)
Urbach energy (E) (eV)
Kth
Pure Smv0 Smv1 Smv2 Smv3 Smv4 Smv5
315 323 328 338 341 343 345
3.94 3.86 3.78 3.67 3.64 3.62 3.60
3.92 3.84 3.77 3.65 3.62 3.61 3.59
3.91 3.85 3.75 3.65 3.61 3.59 3.58
0.2544 0.2604 0.2666 0.2754 0.2770 0.2785 0.2793
0.110 0.088 0.088 0.088 0.087 0.087 0.088
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separation is noticed when content of V2O5 increases in the glass network. The infrared transmission spectra of Na2O–SiO2–ZrO2 codoped Sm3+:V4+ glasses contain different structural units. Within the glass region, rare-earth ion Sm2O3 content is present, due to this there is no significant difference is observed, but may be shifted to lower frequency. The glass system consists of Na2O causes some of the oxygen atoms are bounded by silicon atoms and termed as bridging oxygen. Due to this, Si–O–Si rocking bands are observed at 470 cm1 in the glass system [31]. The percentage of non-bridging oxygen increases with an increases vanadium in content in the glass network V–O–V bending vibrations are present at around 640–660 cm1. Due to the presence of intermediate oxides ZrO2, Zr–O–Zr/ZrO4 structural units are present in the glass network at 730–760 cm1 [51]. Due to the increase in non-bridging ions some bonds are replaced and Si–O–Si symmetric stretching vibrations are observed at 800–900 cm1. The band observed at around 960–970 cm1 is obtained due to the presence of Si–O–Zr structural units [52]. The deformed vibrations or stretching bands are observed at around 1500–1700 cm1 exists due to form of OH groups in NSZ glasses. The NSZ codoped glasses are characterized by the Raman spectra. In these Raman spectra we can observe the similar patterns with the presences of Sm3+ ions in the glass matrix as the bands are shifted towards lower frequency. The spectra of all the glasses are correlated with the IR spectra that the Raman spectra of glasses indicates the vibrational bands at around 350–365 cm1 is due to the Si–O–Si asymmetric vibrations [51]. With the addition of V2O5 in the composition range 0.2–1.0 mol%, the V–O–V vibrational band and combination of another band are observed around 600 cm1 [53]. The band around 800 cm1 causes Si–O–Si symmetric stretching vibrations and at around 900 cm1. The band is observed due to the Si–O–Zr vibrational units [54] or stretching vibrations of vanadium and at around 1070 cm1 there is a Si–O– Si vibrations are observed in the Raman Spectra of codoped Sm3+:V4+: Na2O–SiO2–ZrO2: glasses. Fig. 11 shows the EPR spectra of Na2O–SiO2–ZrO2: Sm3+:V4+ glasses. From this EPR spectra the increased intensity of the signals are observed with an increased the concentration of V2O5, usually vanadium ions seems to exist mainly in V4+ and V5+ state. During the preparation of glasses at high temperature there is a possibility for the following redox equilibrium is takes place 2V5+ + O2 ? 2V4+ + 1/2O2. In this region, the presence of the larger concentration of V4+ ions may also be due to exchange coupling between V3+ ions (if any) and V4+ ions. The spectra of V4+ ions are found to exist in either threefold symmetry or fourfold symmetry. This describe the crystal field of V4+ ions in glasses and the V4+ ions in the NSZ glasses existing in octahedral coordination with a tetragonal compression and having C4v symmetry. An octahedral site with a tetragonal compression gives the value of g|| > g\ > ge [55–60]. From these observations, it is suggested that the paramagnetic V4+ ion in the glass of vanadyl ion VO2+ is in an octahedral
environment with tetragonal distortion. The acquired hyperfine values of the present study suggests a lesser distortion within the glass matrix. This quantitative analysis of EPR result indicates that the ratio of Dg||/Dg\ is observed to decrease gradually with ion concentration of V2O5 indicating an increasing degree of distortion of the VO6 octahedron. The molecular orbital coefficient values indicate that the degree of covalence in V–O–r bonds (b2) and pbonding with the vanadyl oxygen (e2 p ) of all glasses has covalence [61–63]. This EPR study indicates that the tetragonal distortions decrease with increasing V2O5 concentration in the NSZ codoped Sm3+:V4+ glasses. The absorption spectrum of Na2O–SiO2–ZrO2: Sm3+:V4+ glasses, the transition in the absorption spectrum of Sm3+ ions starts from the ground state 6H5/2 raising to the various excited states. The transitions observed in the absorption spectrum with (f–f) transition are almost overlapping with the surrounding ions. The spectrum consists of V4+ ion belongs to d1 configuration. Vanadyl ion exhibited the three absorption bands on the basis of energy level scheme of VO2+ ions in a ligand field C4v symmetry. The transitions are 2B2 ? 2Bg, 2B2 ? 2Eg and 2B2 ? 2A1, for the present glasses exhibit only first two transitions are observed. The largest intensity of the half width of these bands is observed that indicating the presence of the concentration of VO2+ ions in these glasses. The optical band gap for direct and indirect transitions of the sample is found to decrease with an increasing the concentration of dopant V2O5 in the glass matrix due to increase of non-bridging oxygen ions. The observed theoretical optical basicity is found to decrease with an increasing concentration of dopant indicating an increase in covalent nature of the glasses. Conventional Judd–Ofelt (J–O theory) parameter has been calculated from the absorption spectra of Sm3+ ions. The absorption spectra of rare earth ions are useful to understand the radiative properties. The absorption line arising from 4f M 4f electronic transition can reflect an electric dipole, a magnetic dipole or an electric quadrapole characteristic. The electric dipole transitions between two states within 4f configuration are forbidden, while magnetic dipole and electric quadrapole transitions are allowed. The intensity of the absorption bands can be estimated by using oscillator strength fexp, which is calculated from the absorption spectra by using following equation
F exp ¼ 4:318 109
Z
eðmÞdv dm
ð11Þ
where e(m) denotes the molar extinction coefficient at average energy m in cm1. According to the f–f intensity model of the J–O theory, [64] the calculated oscillator strength from initial state to an excited state are described by the expression
f ðwJ; w0 J 0 Þ ¼
X 2 8p2mcv ðn2 þ 2Þ2 X XkðwJjjU k jjw0 J0 Þ 9n 3hð2J þ 1Þ k¼2;4;6
ð12Þ
where m refer to the mass of the electron, c is the velocity of light in vacuum, h is the plank’s constant, n is the refractive index of
Table 7 Theoretical and experimental oscillator strength of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses. Transition 6H5/2? Smv0
Smv1
Smv2
Smv3
Smv4
Smv5
fcal (106) fexp (106) fcal (106) fexp (106) fcal (106) fexp (106) fcal (106) fexp (106) fcal (106) fexp (106) fcal (106) fexp (106) 6
F9/2 F7/2 6 F5/2 6 F3/2 6 F1/2 6 H15/2
2.0276 3.2298 2.2309 1.3654 0.6120 0.4441
Rms deviation
±0.0805
6
2.12798 3.29876 2.33568 1.4654 0.62965 0.4964
2.22356 3.3239 2.4309 1.5683 0.6820 0.6534 ±0.0465
2.2374 3.3289 2.3219 1.5967 0.6902 0.6487
2.2178 3.2654 2.2439 1.3748 0.6290 0.556 ±0.0800
2.0276 3.2896 2.2367 1.3657 0.6548 0.5846
2.0163 3.1292 2.219 1.3098 0.6018 0.4398 ±0.0258
2.0676 3.1598 2.2249 1.3262 0.6125 0.4367
2.0154 3.1146 2.2567 1.3983 0.6062 0.4561 ±0.0202
2.0168 3.1393 2.2309 1.3679 0.6164 0.4679
2.0726 3.2532 2.2093 1.3768 0.6156 0.4344 ±0.0510
2.1876 3.2923 2.2039 1.3567 0.6198 0.4545
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Table 8 J–O intensity parameters of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses. Glass samples
X2 1020 (cm2)
X4 1020 (cm2)
X6 1020 (cm2)
Smv0 Smv1 Smv2 Smv3 Smv4 Smv5
3.65 3.81 3.72 3.68 3.63 3.59
3.31 3.52 3.47 3.43 3.39 3.35
2.42 2.46 2.43 2.38 2.34 2.31
refraction of the glass, m is the frequency of the transition wJ ? w0 J0 , Xk (k = 2, 4 and 6) are the J–O intensity parameters and ||Uk|| are the doubly reduced matrix elements of the unit tensor operator of the rank k = 2, 4 and 6 which are evaluated from the intermediate coupling approximation for a transition wJ ? w0 J0 . The experimental oscillator strengths of absorption bands of Sm3+ doped glass are determined from the known values of Sm3+ concentration, sample thickness, peak position and peak areas by using the Eq. (11). By applying least square fitting procedure to determine the J–O intensity parameters X2, X4 and X6 using experimentally measured oscillator strength, the obtained values are presented in Table 7. The J–O intensity parameters determined in the present glass network are found to be in the order X2 > X4 > X6. As shown in Table 8. The rare earth ions that occupy different coordination site with non-centro symmetric potential contribute significantly to X2 [65–67]. The parameter X2 is related to the covalence and structural changes of the Sm3+ ion and X4 and X6 are related to the long-range effect. They are strongly influenced by the vibration levels associated with the central rare earth ions bound to the ligand atoms. The Photoluminescence spectra of the codoped Sm3+:V4+ NSZ glass system exhibit four emission transitions due to Sm3+ ions in which transition 4G5/2 ? 6H7/2 (604 nm) has a strong orange red emission. The transition 4G5/2 ? 6H7/2 with DJ = ±1 is not only
a magnetic dipole (MD) allowed one, but it is also an electric dipole (ED) dominate [68,69], the other transition 4G5/2 ? 6H9/2 is purely an electric dipole. Hence, the intensity ratio of electric dipole to magnetic dipole transition has been used to measure the symmetry of the local environment of the trivalent 4f ions. In this 4G5/ 6 3+ ion is more intense than 6H5/2 con2 ? H9/2 transition of Sm forming the asymmetric nature of the glass host. In the present glass system the concentration of Sm3+ was fixed at 1 mol%. We observed an increase in vanadium; the energy transfer takes place from vanadium to samarium. However, it will decrease due to the concentration quenching between the ions [70]. The energy transfer mechanism between Sm3+:V4+ codoped NSZ glasses with variation in concentration are found cause dipole–dipole interaction. The small energy separation between the two levels of Sm3+ to V4+ indicates that they are thermally coupled to each other and the population ion at the two levels with a fixed concentration will depend on the temperature of the glass. This dependence of temperature is due to energy transfer or by multiphonon relaxation. Fig. 12 represents the energy level scheme for all the observed absorption, excitation and emission transitions of Sm3+:V4+ions [71,72]. The possible energy transfer happens from 2E ? 2T2 level of vanadium ion [73,74] to 6F1/2 and 6F9/2 of Sm3+ ions. Hence Sm3+ ion gets excited from 6F1/2 to 4F3/2 and 6F9/2 to 4M15/2 and diexcited to 4G5/2 through non-radiative decay and there by strengthens the emission transition from 4G5/2 of Sm3+ ions. This causes the increases in the intensity of Sm3+ ions rather than the vanadium ions. The various radiative properties are calculated from the luminescence spectra are presented in Table 9. The radiative properties of any of Sm3+ ions depends on the number of facts such as network former or modifier of the glasses. The parameters br (i.e. the branching ratio) of the luminance transitions describe the lasing power of the potential laser transition. Among various transitions of the glass network 4G5/2 ? 6H7/2 are found to have the highest values of br valued among all the glasses [75]. These transitions are considered as a possible laser transition and
Fig. 12. Energy level diagram of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses.
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K. Neeraja et al. / Journal of Molecular Structure 1054–1055 (2013) 339–348 Table 9 Various radiative properties of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses. Glass samples Transitions from 4G5/2
6
H5/2 6 H7/2 6 H9/2 6 H11/2
Smv0
Smv1
Smv2
Smv3
Smv4
Smv5
A (s1)
b (%)
A (s1)
b (%)
A (s1)
b (%)
A (s1)
b (%)
A (s1)
b (%)
A (s1)
b (%)
56.28 200.16 108.62 25.91
14.39 51.20 27.78 6.63
61.84 212.32 114.75 26.98
14.87 51.05 27.59 6.49
58.96 209.65 111.26 26.19
14.52 51.63 27.40 6.45
57.08 208.74 110.87 26.35
14.16 51.79 27.51 6.54
57.37 207.45 110.82 26.69
14.26 51.56 27.54 6.63
57.44 208.67 109.61 26.55
14.28 51.87 27.25 6.60
AT = 390.97
AT = 415.89
AT = 406.06
AT = 403.04
AT = 402.33
AT = 402.27
2. The characterisation of the samples by XRD, EDS technique have indicate that the glasses has amorphous nature and the samples contained well defined and randomly distributed grains at different phases. 3. The IR and Raman spectral studies give valuable information regarding bonding nature of different structural units in the glass matrix. 4. The ESR spectrum confirms that the majority of vanadyl ions are V4+ oxidation state. 5. The optical absorption spectra could successfully explain J– O parameters of Sm3+ ions that indicate the highest covalent environment exits in the glass network. 6. According to the luminescence spectra, the highest value for 4G5/2 ? 6H7/2 transition among various other transitions in the glass system resulting the greatest value indicating that these glasses exhibit better lasing action.
Acknowledgement
Fig. 13. The color space chromaticity diagram of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses.(For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
References
Table 10 The color coordinates of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses. S. no.
Glass samples
1 2 3 4 5 6
Smv0 Smv1 Smv2 Smv3 Smv4 Smv5
The author is greatly thankful to University Grants Commission, Govt. of India, New Delhi for the sanction of Meritorious Scholarship under UGC-BSR scheme to carry out the present research work.
Color coordinates X
Y
0.2365 0.2476 0.3056 0.3022 0.2826 0.3197
0.1074 0.1086 0.1666 0.1626 0.1546 0.1803
indicate that the glasses exhibit better lasing action. For better identification of luminescence properties of the prepared glasses, chromaticity coordinates are calculated from the emission spectrum. The CIE system characterizes the color by a two color coordinate x and y which specify the point on the chromaticity diagram as shown in Fig. 13. The pure white color source coordinate is 0.33, 0.33. The two color coordinates x and y are nearly 0.3197, 0.1666 as indicated in Table 10. This implies that this material can be used for optical devices. 5. Conclusions 1. The physical properties of the glasses vary non-linearly with increase of the concentration of V2O5 which affected all related physical parameters of the system.
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Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc
Spectroscopic properties of Sm3+ and V4+ ions in Na2O–SiO2–ZrO2 glasses K. Neeraja, T.G.V.M. Rao, A. Rupesh Kumar, V. Uma Lakshmi, N. Veeraiah, M. Rami Reddy ⇑ Department of Physics, Acharya Nagarjuna University, Nagarjuna Nagar 522 510, India
h i g h l i g h t s XRD techniques are indicates that the glasses have amorphous nature. 4+
ESR spectrum indicates the vanadyl ions can exists in V
state. 3+
J–O parameters are indicates the strong electrostatic field exists around Sm
a r t i c l e
i n f o
Article history: Received 26 June 2013 Received in revised form 23 September 2013 Accepted 23 September 2013 Available online 30 September 2013 Keywords: XRD EDS Infrared (FT-IR) Raman EPR Optical absorption and luminescence spectra
ions.
a b s t r a c t Na2O–SiO2–ZrO2 glasses of Sm3+ ions with and without V2O5 are characterized by spectroscopic and optical properties. The XRD and EDS spectra of the glass samples reveal an amorphous nature with different compositions within the glass matrix. The Infrared and Raman spectral studies are carried out and the existence of conventional structural units are analyzed in the glass network. The ESR spectra of the glass samples have indicating that a considerable proportion of vanadium ion exists in V4+ state. The optical absorption spectra of these glasses are recorded at room temperature, from the measured intensities of various absorption bands the Judd–Ofelt parameters X2, X4 and X6 are calculated. The photo-luminescence spectra recorded with excited wavelength 400 nm, five emission bands are observed; in this the energy transfer probability takes place between Sm3+ and V4+ ions. Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction The study of oxide glasses with rare earth ion is of great importance due to the wide range of applications in sensiting solid state and glass lasers, optical fiber and optical detectors for fluorescent display devices. Due to these optical properties Sm3+ ions in the glass network may change the chemical environment. They have high emissions efficiency to recognize the spectral properties helpful to design of new glass composition for photonic materials [1– 5]. The presence of alkali oxides like sodium act like a network modifier in the glass network enhancing the rare earth suitability of the glasses to produce non-bridging oxygen atoms (NBO) that helps in the design of high efficiency in short length fiber amplifiers [6–9]. Silicate, known as a glass forming oxide enters into alkali metal oxide in glass matrix eventually changes the glass network leading to the formation of non-bridging oxygen atoms. Silicate has its applications in different areas of electronics and other fields due to high chemical resistance, coefficient of thermal expansion and good UV transparency [10–12]. ⇑ Corresponding author. Tel.: +91 9866804948; fax: +91 8632293378. E-mail address: [email protected] (M. Rami Reddy). 0022-2860/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.molstruc.2013.09.038
Zirconium oxide is one of the intermediate oxides that enters the sodium silicate glasses and improves the transparency, electrical resistivity, chemical inertness. This results in hike of the refractive index, decreases in the cutoff wavelength and reduction photochromism of the glasses and helps to improve the optical and mechanical properties [13–17]. Vanadium is one the transition metal oxide that displays excellent properties of electrochromisim of blue M green M yellow and has unique properties because of its semiconducting properties that is the result of electron hopping between the ions. Vanadium exists in three possible oxidation states i.e. V3+, V4+ and V5+. The V2O5 can be incorporated in the rare earth glasses it undergoes radiative and non-radiative transitions are takes place with in glass matrix. Due to this the energy transfer process increases the laser efficiency of the glasses and also has significant applications in research and development of new laser materials [18–25]. Keeping in view of the above interesting results, the present work makes a quantitative evaluation of the radiative and non-radiative energy transfer in the Sm2O3:V2O5 codoped sodium silicon zirconium (NSZ) glasses are used for the present study. In the present study the spectroscopic characteristics of Sm3+ ions and the energy transfer probability in (Sm3+:V4+) co doped NSZ
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glasses is monitored, investigating the structural changes that takes place due to oxidation state of vanadium. The shifting role of modifier ions varied in the spectroscopic and optical properties of Sm2O3 ions in Na2O–SiO2–ZrO2 glasses co doped with V2O5 using XRD, EDS, EPR, FT-IR, Raman spectra, Optical Absorption and Luminescence studies are recorded. 2. Experimental technique Analytical reagents with 99.9% purity of Na2CO3, SiO2, ZrO2, Sm2O3 and V2O5 are used to prepare the glasses. Here samarium and vanadium are employed as dopants in the glass network. Glasses were prepared by using melt quenching technique; in this calculated quantities of chemicals in mol% were taken in an agate mortar and then powdered to obtain homogeneous mixture. The mixture is taken in silica crucible and heated for about 1 h in an automatic temperature controlled furnace at a temperature range 1350–1450 °C. The melt is quickly poured into preheated brass mould so as to obtain the required shape. The obtained samples were immediately transferred to the muffle furnace of 450 °C temperature for annealing. The muffle furnace containing samples was switched off immediately and left to cool at room temperature at a rate of 25 °C/h to avoid thermal stress and to get the structural stability. Later the samples were polished to final dimensions of 1 cm 1 cm 0.2 cm. The glass samples are transparent and appear to have good optical quality. The composition of the prepared glasses containing variable amount of contents are given in Table 1. Density of the glasses was determined to an accuracy of (±0.0001) by the standard Archimedes Principle using o-xylene (99.9% pure) as buoyant liquid and the refractive index of the glass sample is measured by using Abbe’s refractrometer. The X-ray diffraction spectrum is recorded on a diffractometer with copper target (XRDARLX’TRA) and nickel filter operated at 40KV, 30 mA. The Energy Dispersive Spectroscopy measurements were conducted on a Thermo Instruments Model Noran System 6 attached to scanning electron microscope. The electron spin resonance (ESR) spectra of the fine powder of the sample were recorded at room temperature. Infrared Transmission Spectra are recorded on a JASCO-FT-IR -53000 spectrophotometer with resolution of 0.1 cm1 in the spectral range 400–4000 cm1 using KBr pellets (300 mg) containing the pulverized sample (1.5 mg). The Raman Spectra (model Nexus 670 Nicolet – Madison – WI, USA) is recorded on Fourier transform Raman spectrometer with resolution of 4 cm1 in the 400–1500 cm1. The optical absorption (UV–Vis) Spectra are recorded on JASCO, V-570 Spectrophotometer from 200 to 1800 nm with Spectral resolution of 0.1 nm. The luminescence Spectra are recorded at room temperature on a photon Technology International (PTI) spectroflurometer with excited wavelength 400 nm from 300 to 1200 nm. 3. Results 3.1. Physical properties To understand the physical properties of the glasses, various parameters are calculated, i.e. practically measured density (d)
and refractive index (The error in density measurements and refractive indices are estimated to be ±0.004 g/cm3 and ±0.0001 respectively) are calculated. Along with this function, some other physical parameters also calculated [26–29] using conventional formulae such as vanadium ion concentration (Ni), mean ionic separation (ri), polaron radius (rp), field strength (Fi), electronic polaraizability (a), reflection loss, Molar refractivity (RM) and optical dielectric constant (e) which are presented in the Table 2. Fig. 1 shows the variation of density and refractive index as a function of glass samples. Fig. 2 represents the ionic concentration and electronic polaraizability as a function of x mol% (x = 0.2, 0.4, 0.6, 0.8, 1.0) of dopant. 3.2. X-ray diffraction spectra The amorphous nature of the Sm3+:V4+ co-doped NSZ glasses was confirmed by X-ray diffraction spectra, which Shows a broad bump around the centered 27° (=2h). There are no observed sharp lines which shows that all the prepared samples confirms the amorphous nature and it is shown in Fig. 3. 3.3. Energy Dispersive Spectroscopy From the Energy Dispersive Spectroscopy (EDS), the chemical compositions of the glasses were determined as shown in Fig. 4. The inset figure shows the electronic image spectrum of the glass sample of 1 mol% V2O5. The analysis indicates the presence of sodium (Na), silicon (Si), zirconium (Zr), samarium(Sm), oxygen (O), carbon (C), and vanadium (V) elements in the glass network. 3.4. Fourier transforms Infrared transmission spectra (FT-IR) The Fourier transforms Infrared transmission spectra gives information about the various vibrational modes and also provides structural information of the glass network. The spectra of undoped and doped Sm3+:V4+ codoped NSZ glasses are shown in Fig. 5. The spectral features are analyzed from the studied glasses show the vibration bands without any obvious variations. The observed IR spectral bands are given in Table 3. The spectra exhibit a series of bands [30] one at about 470 cm1, the second band at around 640–660 cm1 and the third at around 730–760 cm1. Two bands are located at around 800–900 cm1 and one sharp band with a peak is located at about 960–970 cm1. Another belonging to the OH groups is found around 1500–1700 cm1 [31]. 3.5. Raman spectra Raman spectra are used to characterize the local arrangement of the structure of the glasses and also give information about the structural properties that would support the Infrared transmission spectra. Fig. 6 represents the Raman spectra of the undoped and doped Sm3+:V2O5 NSZ glasses. The Raman spectra of the glasses and band positions are presented in Table 4. The spectra of NSZ glasses have revealed a peak at round 350–365 cm1 and structural vibrations are observed at around 800 cm1. In the spectrum
Table 1 Composition of the studied glasses (batch mol%). S. no.
Glass
Na2O (mol%)
SiO2 (mol%)
ZrO2 (mol%)
Sm2O3 (mol%)
V2O5 (mol%)
1 2 3 4 5 6 7
Pure Smv0 Smv1 Smv2 Smv3 Smv4 Smv5
40 40 40 40 40 40 40
55 54 54 54 54 54 54
5 5 4.8 4.6 4.4 4.2 4
– 1 1 1 1 1 1
– – 0.2 0.4 0.6 0.8 1.0
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K. Neeraja et al. / Journal of Molecular Structure 1054–1055 (2013) 339–348 Table 2 Various physical properties of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses. Physical Parameters 3
Density d (g/cm ) (±0.004) Average molecular weight (M) Ion concentration Ni (1020 ions/cm3) (±0.005) Interionic distance ri (Å) (±0.005) Polaron radius rp (Å) (±0.005) Field strength Fi (1015 cm2) (±0.005) Refractive index n (±0.0001) Reflection loss Molar reflectivity RM (cm3) (±0.005) Electronic polaraizability (ae) (1022 ions/cm3) (±0.005) Optical dielectric constant (e0) (±0.005)
Pure
Smv0
Smv1
Smv2
Smv3
Smv4
Smv5
2.679 63.99 – – – – 1.674 0.033 8.969 – 2.803
2.692 66.88 – – – – 1.662 0.032 9.197 – 2.763
2.718 67.00 0.488 27.35 11.02 2.47 1.663 0.032 9.131 18.106 2.765
2.780 66.71 1.004 21.51 8.66 3.99 1.665 0.032 8.909 8.832 2.772
2.785 66.63 1.510 18.77 7.56 5.24 1.667 0.033 8.904 5.885 2.778
2.769 66.55 2.005 17.08 6.88 6.33 1.666 0.033 8.940 4.431 2.777
2.762 66.46 2.502 15.86 6.39 7.33 1.667 0.033 8.957 3.552 2.778
Fig. 3. XRD spectra of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses.
Fig. 1. Variation of density and refractive index with glass sample of Na2O–SiO2– ZrO2: Sm3+:V4+ codoped glasses.
Fig. 4. EDS spectra of 1 mol% V2O5 in Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses.
the nature of its bonding with the nearest neighboring ligands. The EPR spectra recorded at room temperature for the present investigated NSZ: Sm3+:V4+ co-doped glasses. No signals are observed for the undoped glasses. When V2O5 are introduced into the glass matrix, the EPR resonance spectra exhibit eight parallel and eight perpendicular lines arising from the unpaired 3d1 electron of VO2+ ions with 51V (I = 7/2) isotope in an axially symmetric field. The axial spin-Hamiltonian for hyperfine interaction is used to describe the spectra of V4+ ions [35]. Fig. 2. Variation of ionic concentration and electronic polaraizability of Na2O–SiO2– ZrO2: Sm3+:V4+ codoped glasses.
contains V2O5, stretching vibrations are observed at around 600 cm1 and another two band is observed at 900 cm1 and 1070 cm1 [32–34].
3.6. Electron paramagnetic resonance spectra Electron paramagnetic resonance spectra is a method to understand the symmetry of surroundings of the paramagnetic ion and
H ¼ b½g jj Bz Sz þ g ? ðBx Sx þ By SyÞ þ Ajj Sz Iz þ A? ðSx Ix þ Sy Iy Þ
ð4Þ
Here b denotes Bohr magneton, g||, g\ and A||, A\ denotes the components of the hyperfine coupling tensor, Bx, By and Bz denotes components of the magnetic field, Sx, Sy, Sz and Ix, Iy, Iz are the spin operator of the electron and the nucleus. The magnetic field positions for the parallel and perpendicular hyperfine peaks are based on the second order perturbation terms are
"
# A2? 63 m2 Bjj ðmÞ ¼ Bjj ð0Þ mAjj 4 1Bjj ð0Þ
ð5Þ
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Fig. 6. Raman spectra of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses.
Fig. 5. FT-IR spectra of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses.
2 3 2 A2jj þ A? 5 63 m2 B? ðmÞ ¼ B? ð0Þ mA? 4 4 4B? ð0Þ
e2 p ¼ ð6Þ
From the above equation m refer to the nuclear spin magnetic quantum number, bearing values ±7/2, ±5/2, ±1/2; B|| (0) = h/g||b and B\(0) = h/g\b. From the above parameters, the dipolar hyper fine coupling parameters P = 2dbbN r3 and the Fermi contact interaction (K), are evaluated [36] using the expression
Ajj ¼ P½ð4=7Þ-K þ ðg jj g e Þ þ ð3=7Þðg ? g e Þ
ð7Þ
A? ¼ P½ð2=7Þ-K þ ð11=14Þðg ? g e Þ
ð8Þ
In the equation, ge = 2.0023 and refer to the g factor of the free electron. The term P and K in the above equation result from the S-character of the magnetic spin of the vanadium. Generally the S-character is due to the partial unpairing or polarization of the inner s-electron gives the interaction with the unpaired d electrons. The values Dg||/Dg\ are also calculated for the tetragonality of the vanadium site. The molecular bonding coefficient b2 and e2 p are evaluated by correlating the EPR and optical data using [37] the given expressions
b2 ¼
ðg e g jj ÞDjj 8k
ð9Þ
ðg e g ? ÞD? 8k
ð10Þ
In the above equation, k is the free-ion value of spin orbit coupling constants for the vo2+ ions and is taken as 170 cm1. D|| and D\ are energies of the electronic transitions from 2B2 ? 2Bg and 2 B2 ? 2Eg respectively. The above evaluated values from these spectra along with the other pertinent data are furnished in Table 5. 3.7. Optical absorption spectra The absorption spectra of Sm3+:V4+ ions codoped NSZ glasses show a large number of bands; the observed bands are assigned on the basis of the reported energy levels [38–41] of Sm3+ ions of different glass hosts. With the addition of V2O5, the absorption intensity enhances and exhibit more absorption band. The bands are observed at 402, 470, 1070, 1221, 1260, 1360, 1370, 1465, 1522 nm [42,43] these bands are related to samarium (Sm3+) ions resulting due to the different transitions are from 6H5/2 ? 6P3/2, 4 I13/2 + 4I11/2 + 4M15/2, 6F9/2, 6F7/2, 6F5/2, 6F3/2, 6F1/2, 6H15/2. When V2O5 is added to the glass network two more additional bands are observed at 683 and 1070 nm due to the transitions 2 B2 ? 2Bg and 2B2 ? 2Eg. Thus, from these optical absorption spectra totally nine bands are observed for Sm3+:V4+ doped NSZ glasses as shows in Fig. 7. from the observed edge, we have evaluated the
Table 3 The FT-IR band positions of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses. Glass samples
Band assignments
Pure
Smv0
Smv1
Smv2
Smv3
Smv4
Smv5
470 – 732 – 890 961 1517 1695
471 – 742 – 884 968 1522 1695
470 648 743 836 884 964 1527 1696
470 653 743 818 883 963 1522 1695
471 653 742 816 884 965 1522 1695
470 652 743 816 888 963 1524 1696
471 653 743 818 889 965 1524 1696
Bending and rocking motion of Si–O–Si V–O–V bending vibrations Zr–O–Zr/ZrO4 structural units V–O–V chains Si–O–Si symmetric stretching vibrations Si–O–Zr units Stretching mode of Si–OH Water molecular vibrations
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Band assignments
Pure
Smv0
Smv1
Smv2
Smv3
Smv4
Smv5
353 – 856 949 1090
353 – 854 947 1091
355 617 854 947 1091
357 617 852 949 1092
361 615 853 949 1091
361 612 856 947 1092
361 612 856 947 1091
Si–O–Si rocking vibrations V–O–V vibrations/combinations of various vibrations Si–O–Si bending vibrations Si–O–Zr rocking vibrations Si–O–Si stretching vibrations
Table 5 The spin-Hamiltonian parameters and molecular orbitals coefficients for Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses. Glass code g|| ||
g\
A||
Smv0 Smv1 Smv2 Smv3 Smv4
1.9085 1.9191 1.9191 1.9191 1.9186
183 181 181 181 181
1.8926 1.8967 1.8967 1.8968 1.8966
||
104 cm1 A\ 104 cm1 b⁄2 67 66 66 66 66
0.0471 0.0417 0.0417 0.0417 0.0420
e2 p
g||||
g\
g||
||/g\
0.0863 0.0830 0.0830 0.0830 0.0831
0.0938 0.0832 0.0832 0.0832 0.0837
0.1097 0.1056 0.1056 0.1055 0.1057
0.8550 0.7878 0.7878 0.7886 0.7918
P 104 cm1 K 144.5 140.4 140.4 140.2 140.2
0.8355 0.8476 0.8476 0.8478 0.8479
AIjj
jj
104 cm1 AI? 104 cm1
62.28 62 62 62.2 62.2
53 53 53 52.8 52.8
Fig. 7. Optical absorption spectra of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses.
optical band gap (Eo) of these glasses by drawing Tauc plot between (ahm)1/2, (ahm)2 as a function of hm as per the given equation
aðmÞhm ¼ Cðhm Eo Þn
ð1Þ
Here C is a constant and the exponent (n) can take values 1/2 and 2 for indirect, direct transitions in glasses respectively [44]. Tauc plots for direct transition in Fig. 8(a) and indirect transition are shown in Fig. 8(b). Extrapolating the linear portion of these plots as (ahm)1/ 2 = 0, (ahm)2 = 0 gives optical band gap, along with the theoretical optical band gap energy also calculated using equation E = hc/k. Here h is the plank’s constant, c is the velocity of light and k cutoff wavelength respectively. The value of DE is calculate by taking the reciprocal of the slope of the linear portion in the lower photon energy region of ln(a) verses hm plot are shown in Fig. 9. Urbach energy which corresponds to the width of localized states and characterizes the degree of disorder in the glass systems. The value of DE in the present work lies in the range 0.25–0.27 eV for all the glasses. The increase in Urbach energy with increasing the concentration of V2O5. In addition to this, the theoretical optical basicity (Kth) of the glasses can be calculated for the Sm3+:V2O5 doped NSZ glasses [45,46] by using the formula
Fig. 8. Tauc plots to evaluate (a) direct band gap, (b) in-direct band gap of Na2O– SiO2–ZrO2: Sm3+:V4+ codoped glasses.
Kth ¼
n X Zi ri i¼1
Zdi
ð2Þ
where n denotes the total number of cations present, Zi denotes the oxidation number of the ith cation, ri denotes the ratio of the
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Fig. 9. A plots of ln(a) and hm for Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses.
number of the ith cation to the number of oxides present and di denote basicity moderating parameters of ith cation. The basicity moderating parameter is calculated from the following equation
di ¼ 1:36ðxi 0:26Þ
Fig. 10. Luminescence spectra of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses.
ð3Þ
where xi represents the pouling electro negativity of the cation. The theoretical and evaluated values of cutoff wavelength, theoretical band gap, direct and indirect band gap and the theoretical optical basicity (Kth) are presented in Table 6. 3.8. Photoluminescence spectra The Photoluminescence spectra of Sm3+:V4+ doped NSZ glasses are recorded at room temperature with excited wavelength 400 nm in region 450–900 nm. When Sm3+ ions are excited at 6 P3/2 level (402 nm), the initial population relaxes finally to the 4 G5/2 level. Between 6P3/2 and 4G5/2 levels, there are several intermediate levels with smaller energy difference, which encourage their efficient non-radiative relaxation there by leading to the population at the 4G5/2 state. This state is distinct from the intermediate lower state i.e. 6F11/2. It could be stated that radiative transitions and relaxations by non-radiative energy transfer are the two main processes, which could finally depopulate the 4G5/2 state. The emission spectra of the NSZ glasses containing Sm3+ ions exhibit four emission transitions, which are assigned to 4 G5/2 ? 6F5/2 (576 nm), 4G5/2 ? 6F7/2 (604 nm), 4G5/2 ? 6F9/2 (648 nm) and 4G5/2 ? 6F11/2 (708 nm) [47,48]. By the addition of V2O5 another band is observed at round 782 nm with the transition 2 E ? 2T2 [49,50]. The Fig. 10 shows the luminescence spectra of Sm3+:V4+ codoped NSZ glasses. 4. Discussions Among the physical properties, density is an effective tool to explore the degree of structural compactness of the glasses. In the present work, increase in density is observed with the increasing content of V2O5 in all the glasses. Basically, when V2O5 enters into
Fig. 11. EPR spectra of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses.
the glass network in two forms, they acts as network modifier at low content and at high content it acts as network forming group. Due to this, non-bridging oxygen content is further increases. The density and refractive index of the observed parameters vary nonlinearly with increasing vanadium concentration. From these observations, the effect of V2O5 in ionic concentration and electronic polaraizability of Sm3+:V2O5 NSZ glasses vary non-linearly. It is observed that both the parameters tend to be inversely proportional to the increase in x mol% of vanadium concentration. The polaraizability is high at x = 1 mol%, whereas, its ionic concentration lower due to feeble ionic mobility and increase in interionic separation (ri) is observed. An eventual decrease in interionic
Table 6 The cutoff wavelength, optical band gaps, Urbach energy and optical Basicity of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses. Glass samples
Cutoff wavelength
Theoretical band gap
Direct band gap (eV)
Indirect band gap (eV)
Urbach energy (E) (eV)
Kth
Pure Smv0 Smv1 Smv2 Smv3 Smv4 Smv5
315 323 328 338 341 343 345
3.94 3.86 3.78 3.67 3.64 3.62 3.60
3.92 3.84 3.77 3.65 3.62 3.61 3.59
3.91 3.85 3.75 3.65 3.61 3.59 3.58
0.2544 0.2604 0.2666 0.2754 0.2770 0.2785 0.2793
0.110 0.088 0.088 0.088 0.087 0.087 0.088
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separation is noticed when content of V2O5 increases in the glass network. The infrared transmission spectra of Na2O–SiO2–ZrO2 codoped Sm3+:V4+ glasses contain different structural units. Within the glass region, rare-earth ion Sm2O3 content is present, due to this there is no significant difference is observed, but may be shifted to lower frequency. The glass system consists of Na2O causes some of the oxygen atoms are bounded by silicon atoms and termed as bridging oxygen. Due to this, Si–O–Si rocking bands are observed at 470 cm1 in the glass system [31]. The percentage of non-bridging oxygen increases with an increases vanadium in content in the glass network V–O–V bending vibrations are present at around 640–660 cm1. Due to the presence of intermediate oxides ZrO2, Zr–O–Zr/ZrO4 structural units are present in the glass network at 730–760 cm1 [51]. Due to the increase in non-bridging ions some bonds are replaced and Si–O–Si symmetric stretching vibrations are observed at 800–900 cm1. The band observed at around 960–970 cm1 is obtained due to the presence of Si–O–Zr structural units [52]. The deformed vibrations or stretching bands are observed at around 1500–1700 cm1 exists due to form of OH groups in NSZ glasses. The NSZ codoped glasses are characterized by the Raman spectra. In these Raman spectra we can observe the similar patterns with the presences of Sm3+ ions in the glass matrix as the bands are shifted towards lower frequency. The spectra of all the glasses are correlated with the IR spectra that the Raman spectra of glasses indicates the vibrational bands at around 350–365 cm1 is due to the Si–O–Si asymmetric vibrations [51]. With the addition of V2O5 in the composition range 0.2–1.0 mol%, the V–O–V vibrational band and combination of another band are observed around 600 cm1 [53]. The band around 800 cm1 causes Si–O–Si symmetric stretching vibrations and at around 900 cm1. The band is observed due to the Si–O–Zr vibrational units [54] or stretching vibrations of vanadium and at around 1070 cm1 there is a Si–O– Si vibrations are observed in the Raman Spectra of codoped Sm3+:V4+: Na2O–SiO2–ZrO2: glasses. Fig. 11 shows the EPR spectra of Na2O–SiO2–ZrO2: Sm3+:V4+ glasses. From this EPR spectra the increased intensity of the signals are observed with an increased the concentration of V2O5, usually vanadium ions seems to exist mainly in V4+ and V5+ state. During the preparation of glasses at high temperature there is a possibility for the following redox equilibrium is takes place 2V5+ + O2 ? 2V4+ + 1/2O2. In this region, the presence of the larger concentration of V4+ ions may also be due to exchange coupling between V3+ ions (if any) and V4+ ions. The spectra of V4+ ions are found to exist in either threefold symmetry or fourfold symmetry. This describe the crystal field of V4+ ions in glasses and the V4+ ions in the NSZ glasses existing in octahedral coordination with a tetragonal compression and having C4v symmetry. An octahedral site with a tetragonal compression gives the value of g|| > g\ > ge [55–60]. From these observations, it is suggested that the paramagnetic V4+ ion in the glass of vanadyl ion VO2+ is in an octahedral
environment with tetragonal distortion. The acquired hyperfine values of the present study suggests a lesser distortion within the glass matrix. This quantitative analysis of EPR result indicates that the ratio of Dg||/Dg\ is observed to decrease gradually with ion concentration of V2O5 indicating an increasing degree of distortion of the VO6 octahedron. The molecular orbital coefficient values indicate that the degree of covalence in V–O–r bonds (b2) and pbonding with the vanadyl oxygen (e2 p ) of all glasses has covalence [61–63]. This EPR study indicates that the tetragonal distortions decrease with increasing V2O5 concentration in the NSZ codoped Sm3+:V4+ glasses. The absorption spectrum of Na2O–SiO2–ZrO2: Sm3+:V4+ glasses, the transition in the absorption spectrum of Sm3+ ions starts from the ground state 6H5/2 raising to the various excited states. The transitions observed in the absorption spectrum with (f–f) transition are almost overlapping with the surrounding ions. The spectrum consists of V4+ ion belongs to d1 configuration. Vanadyl ion exhibited the three absorption bands on the basis of energy level scheme of VO2+ ions in a ligand field C4v symmetry. The transitions are 2B2 ? 2Bg, 2B2 ? 2Eg and 2B2 ? 2A1, for the present glasses exhibit only first two transitions are observed. The largest intensity of the half width of these bands is observed that indicating the presence of the concentration of VO2+ ions in these glasses. The optical band gap for direct and indirect transitions of the sample is found to decrease with an increasing the concentration of dopant V2O5 in the glass matrix due to increase of non-bridging oxygen ions. The observed theoretical optical basicity is found to decrease with an increasing concentration of dopant indicating an increase in covalent nature of the glasses. Conventional Judd–Ofelt (J–O theory) parameter has been calculated from the absorption spectra of Sm3+ ions. The absorption spectra of rare earth ions are useful to understand the radiative properties. The absorption line arising from 4f M 4f electronic transition can reflect an electric dipole, a magnetic dipole or an electric quadrapole characteristic. The electric dipole transitions between two states within 4f configuration are forbidden, while magnetic dipole and electric quadrapole transitions are allowed. The intensity of the absorption bands can be estimated by using oscillator strength fexp, which is calculated from the absorption spectra by using following equation
F exp ¼ 4:318 109
Z
eðmÞdv dm
ð11Þ
where e(m) denotes the molar extinction coefficient at average energy m in cm1. According to the f–f intensity model of the J–O theory, [64] the calculated oscillator strength from initial state to an excited state are described by the expression
f ðwJ; w0 J 0 Þ ¼
X 2 8p2mcv ðn2 þ 2Þ2 X XkðwJjjU k jjw0 J0 Þ 9n 3hð2J þ 1Þ k¼2;4;6
ð12Þ
where m refer to the mass of the electron, c is the velocity of light in vacuum, h is the plank’s constant, n is the refractive index of
Table 7 Theoretical and experimental oscillator strength of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses. Transition 6H5/2? Smv0
Smv1
Smv2
Smv3
Smv4
Smv5
fcal (106) fexp (106) fcal (106) fexp (106) fcal (106) fexp (106) fcal (106) fexp (106) fcal (106) fexp (106) fcal (106) fexp (106) 6
F9/2 F7/2 6 F5/2 6 F3/2 6 F1/2 6 H15/2
2.0276 3.2298 2.2309 1.3654 0.6120 0.4441
Rms deviation
±0.0805
6
2.12798 3.29876 2.33568 1.4654 0.62965 0.4964
2.22356 3.3239 2.4309 1.5683 0.6820 0.6534 ±0.0465
2.2374 3.3289 2.3219 1.5967 0.6902 0.6487
2.2178 3.2654 2.2439 1.3748 0.6290 0.556 ±0.0800
2.0276 3.2896 2.2367 1.3657 0.6548 0.5846
2.0163 3.1292 2.219 1.3098 0.6018 0.4398 ±0.0258
2.0676 3.1598 2.2249 1.3262 0.6125 0.4367
2.0154 3.1146 2.2567 1.3983 0.6062 0.4561 ±0.0202
2.0168 3.1393 2.2309 1.3679 0.6164 0.4679
2.0726 3.2532 2.2093 1.3768 0.6156 0.4344 ±0.0510
2.1876 3.2923 2.2039 1.3567 0.6198 0.4545
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Table 8 J–O intensity parameters of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses. Glass samples
X2 1020 (cm2)
X4 1020 (cm2)
X6 1020 (cm2)
Smv0 Smv1 Smv2 Smv3 Smv4 Smv5
3.65 3.81 3.72 3.68 3.63 3.59
3.31 3.52 3.47 3.43 3.39 3.35
2.42 2.46 2.43 2.38 2.34 2.31
refraction of the glass, m is the frequency of the transition wJ ? w0 J0 , Xk (k = 2, 4 and 6) are the J–O intensity parameters and ||Uk|| are the doubly reduced matrix elements of the unit tensor operator of the rank k = 2, 4 and 6 which are evaluated from the intermediate coupling approximation for a transition wJ ? w0 J0 . The experimental oscillator strengths of absorption bands of Sm3+ doped glass are determined from the known values of Sm3+ concentration, sample thickness, peak position and peak areas by using the Eq. (11). By applying least square fitting procedure to determine the J–O intensity parameters X2, X4 and X6 using experimentally measured oscillator strength, the obtained values are presented in Table 7. The J–O intensity parameters determined in the present glass network are found to be in the order X2 > X4 > X6. As shown in Table 8. The rare earth ions that occupy different coordination site with non-centro symmetric potential contribute significantly to X2 [65–67]. The parameter X2 is related to the covalence and structural changes of the Sm3+ ion and X4 and X6 are related to the long-range effect. They are strongly influenced by the vibration levels associated with the central rare earth ions bound to the ligand atoms. The Photoluminescence spectra of the codoped Sm3+:V4+ NSZ glass system exhibit four emission transitions due to Sm3+ ions in which transition 4G5/2 ? 6H7/2 (604 nm) has a strong orange red emission. The transition 4G5/2 ? 6H7/2 with DJ = ±1 is not only
a magnetic dipole (MD) allowed one, but it is also an electric dipole (ED) dominate [68,69], the other transition 4G5/2 ? 6H9/2 is purely an electric dipole. Hence, the intensity ratio of electric dipole to magnetic dipole transition has been used to measure the symmetry of the local environment of the trivalent 4f ions. In this 4G5/ 6 3+ ion is more intense than 6H5/2 con2 ? H9/2 transition of Sm forming the asymmetric nature of the glass host. In the present glass system the concentration of Sm3+ was fixed at 1 mol%. We observed an increase in vanadium; the energy transfer takes place from vanadium to samarium. However, it will decrease due to the concentration quenching between the ions [70]. The energy transfer mechanism between Sm3+:V4+ codoped NSZ glasses with variation in concentration are found cause dipole–dipole interaction. The small energy separation between the two levels of Sm3+ to V4+ indicates that they are thermally coupled to each other and the population ion at the two levels with a fixed concentration will depend on the temperature of the glass. This dependence of temperature is due to energy transfer or by multiphonon relaxation. Fig. 12 represents the energy level scheme for all the observed absorption, excitation and emission transitions of Sm3+:V4+ions [71,72]. The possible energy transfer happens from 2E ? 2T2 level of vanadium ion [73,74] to 6F1/2 and 6F9/2 of Sm3+ ions. Hence Sm3+ ion gets excited from 6F1/2 to 4F3/2 and 6F9/2 to 4M15/2 and diexcited to 4G5/2 through non-radiative decay and there by strengthens the emission transition from 4G5/2 of Sm3+ ions. This causes the increases in the intensity of Sm3+ ions rather than the vanadium ions. The various radiative properties are calculated from the luminescence spectra are presented in Table 9. The radiative properties of any of Sm3+ ions depends on the number of facts such as network former or modifier of the glasses. The parameters br (i.e. the branching ratio) of the luminance transitions describe the lasing power of the potential laser transition. Among various transitions of the glass network 4G5/2 ? 6H7/2 are found to have the highest values of br valued among all the glasses [75]. These transitions are considered as a possible laser transition and
Fig. 12. Energy level diagram of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses.
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K. Neeraja et al. / Journal of Molecular Structure 1054–1055 (2013) 339–348 Table 9 Various radiative properties of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses. Glass samples Transitions from 4G5/2
6
H5/2 6 H7/2 6 H9/2 6 H11/2
Smv0
Smv1
Smv2
Smv3
Smv4
Smv5
A (s1)
b (%)
A (s1)
b (%)
A (s1)
b (%)
A (s1)
b (%)
A (s1)
b (%)
A (s1)
b (%)
56.28 200.16 108.62 25.91
14.39 51.20 27.78 6.63
61.84 212.32 114.75 26.98
14.87 51.05 27.59 6.49
58.96 209.65 111.26 26.19
14.52 51.63 27.40 6.45
57.08 208.74 110.87 26.35
14.16 51.79 27.51 6.54
57.37 207.45 110.82 26.69
14.26 51.56 27.54 6.63
57.44 208.67 109.61 26.55
14.28 51.87 27.25 6.60
AT = 390.97
AT = 415.89
AT = 406.06
AT = 403.04
AT = 402.33
AT = 402.27
2. The characterisation of the samples by XRD, EDS technique have indicate that the glasses has amorphous nature and the samples contained well defined and randomly distributed grains at different phases. 3. The IR and Raman spectral studies give valuable information regarding bonding nature of different structural units in the glass matrix. 4. The ESR spectrum confirms that the majority of vanadyl ions are V4+ oxidation state. 5. The optical absorption spectra could successfully explain J– O parameters of Sm3+ ions that indicate the highest covalent environment exits in the glass network. 6. According to the luminescence spectra, the highest value for 4G5/2 ? 6H7/2 transition among various other transitions in the glass system resulting the greatest value indicating that these glasses exhibit better lasing action.
Acknowledgement
Fig. 13. The color space chromaticity diagram of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses.(For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
References
Table 10 The color coordinates of Na2O–SiO2–ZrO2: Sm3+:V4+ codoped glasses. S. no.
Glass samples
1 2 3 4 5 6
Smv0 Smv1 Smv2 Smv3 Smv4 Smv5
The author is greatly thankful to University Grants Commission, Govt. of India, New Delhi for the sanction of Meritorious Scholarship under UGC-BSR scheme to carry out the present research work.
Color coordinates X
Y
0.2365 0.2476 0.3056 0.3022 0.2826 0.3197
0.1074 0.1086 0.1666 0.1626 0.1546 0.1803
indicate that the glasses exhibit better lasing action. For better identification of luminescence properties of the prepared glasses, chromaticity coordinates are calculated from the emission spectrum. The CIE system characterizes the color by a two color coordinate x and y which specify the point on the chromaticity diagram as shown in Fig. 13. The pure white color source coordinate is 0.33, 0.33. The two color coordinates x and y are nearly 0.3197, 0.1666 as indicated in Table 10. This implies that this material can be used for optical devices. 5. Conclusions 1. The physical properties of the glasses vary non-linearly with increase of the concentration of V2O5 which affected all related physical parameters of the system.
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