- Email: [email protected]
Er codoped Na0.5Bi2.5Nb2O9 ceramics for display and optical storage
Journal of Luminescence 215 (2019) 116626
Contents lists available at ScienceDirect
Journal of Luminescence journal homepage: www.elsevier.com/locate/jlumin
Defect modulated luminescent and photochromic behaviors in Pr/Er codoped Na0.5Bi2.5Nb2O9 ceramics for display and optical storage
T
Yan Zhua, Yang Lva, Yunhui Xiaoa, Haiqin Suna,*, Qiwei Zhanga,b,**, Xihong Haoa,b a
Inner Mongolia Key Laboratory of Ferroelectric-related New Energy Materials and Devices, School of Materials and Metallurgy, Inner Mongolia University of Science and Technology, 7# Arding Street, Kun District, Baotou, 014010, China b Key Laboratory of Integrated Exploitation of Bayan Obo Multi-Metal Resources, Inner Mongolia University of Science and Technology, Baotou, 014010, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Multi-color luminescence Luminescence modulation Photochromism Defects
In order to explore the mechanism of luminescence modulation and photochromism of Na0.5Bi2.5Nb2O9 (NBN)based photochromic materials, the luminescence, photochromism and luminescence modulation properties of Pr3+/Er3+ co-doped NBN ceramics under different sintering atmospheres (Air, O2, and N2) were systematically studied. The results show that the samples exhibit excellent properties of multi-color luminescence (red-green), multi-mode (upconversion/downshifting) luminescence properties. Correspondingly, the upconversion and downshifting emission intensities are significantly decreased for samples sintered at nitrogen. And, the luminescence switching contrast (ΔRt) of the sample sintered in N2 is also obviously lower than the ΔRt values under air and O2 atmospheres upon 405 nm irradiation. Such color and ΔRt value changes under different atmospheres are closely related to defects and traps due to Bi and Na element volatilizations, which are well verified by XPS analysis. Meanwhile, various pattern displays based on photochromic NBN materials can be well achieved with fast response and good fatigue resistance.
1. Introduction Solid-state photochromic compounds (organic and inorganic photochromic materials) have been always considered as a promising material for optical storage, photo-switching, and sensors because of their high sensitivity, fast response time, and excellent fatigue resistance [1–3]. To date, the studies of organic photochromic phenomenon are extensively explored, for example, a dyad composed of photochromic and luminescent dye units, small organic molecules, photoactivatable luminescent proteins (PAFPs), metal complexes with photochromic units, photochromic bisthienylethene and diarylethene (DAET) derivatives, etc [4–6]. However, photochromism of inorganic compounds have rarely been reported. From the earliest study of the photochromic behavior of transition metal-doped SrTiO3 by Faughnan et al., in 1968 [7], the exploration of inorganic photochromism materials has never stopped. Nowadays, many inorganic materials (WO3, TiO2, Pb(Zr,Ti)O3, Sr2SnO4: Eu, BaMgSiO4: Eu, polyoxometalates etc.) have been found to have excellent photochromic properties [8–13]. Compared to the organic photochromic materials, inorganic photochromic materials have many distinct advantages: (i) excellent mechanical strength; (ii) high
thermal stability; and (iii) good chemical stability [14]. Moreover, inorganic photochromic materials are indispensable in high-density optical memories and 3D graphics memory devices [15]. Currently, there are several theoretical models to explain photochromic behavior. For inorganic photochromic materials, the model is mainly based on the presence of color centers or hydrogen bronze under irradiation, and significant changes in the absorption spectrum are thought to be caused by color centers, intervanlence-charge transfer (IVCT), or small-polaron transitions [16–18]. For some polycrystalline or nanocrystalline materials, light absorption is primarily coming from free carriers or trapped carriers [19]. However, these two mechanisms are in principle difficult to achieve non-destructive illuminating readout capabilities, hindering their use in optical memory and switching applications. Recently, luminescent materials based on ferroelectric perovskite compounds have been extensively studied for their potential applications in integrated optoelectronic devices [20–22]. Due to the distinct structure of perovskite-type ferroelectrics, it may involve completely different luminescence modulation mechanisms, and its inherent ferro-/piezoelectric properties have great application value in the field of photochromic and multi-functional devices.
*
Corresponding author. Corresponding author. Key Laboratory of Integrated Exploitation of Bayan Obo Multi-Metal Resources, Inner Mongolia University of Science and Technology, Baotou, 014010, China. E-mail addresses: [email protected] (H. Sun), [email protected] (Q. Zhang). **
https://doi.org/10.1016/j.jlumin.2019.116626 Received 27 May 2019; Received in revised form 9 July 2019; Accepted 13 July 2019 Available online 14 July 2019 0022-2313/ © 2019 Elsevier B.V. All rights reserved.
Journal of Luminescence 215 (2019) 116626
Y. Zhu, et al.
apparently attributed to the characteristic emission of Pr3+ and Er3+ ions. It is found that the combination of Pr3+ and Er3+ ions can exhibit excellent multi-color luminescence (red-green), multi-mode (upconversion/downshifting) luminescence properties. Fig. 3c shows the upconversion (UC) emission spectra of Pr3+/Er3+ co-doped NBN ceramics excited by 980 nm light, there are three emission bands: green emissions in 520–539 nm and 539–570 nm, and a weak red emission in 650–680 nm, which are attributed to the intra 4f–4f electronic transitions of 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 of Er3+, respectively. All emission bands are consistent with those reported by other groups [29–31]. Further, the green emission intensity is significantly stronger than the red emission intensity. Fig. 3d provides the intensity of the highest peak in UC and PL spectrum in different atmospheres. It can be seen that the UC and PL luminescence intensity of sample sintered in O2 is the strongest, obviously higher than that sintered in N2. Fig. 4 shows the UC emission spectra of samples sintered in different atmospheres with pump powers of 20–400 mW and the emission intensity vs. pumping power curves. It can be seen that the UC emission intensity increases with the increase of pump powers. In order to investigate UC mechanisms and photon absorption processes, the number of photons can be calculated according to the relationship between UC emission intensity (Iup) and incident pumping power (P), and UC emission intensity Iup is approximately proportional to the pumping power (P): I ∝ Pn [32], where n is the number of photons involved in the pumping mechanism. The obtained n values are 1.0566 (Air),1.0668 (N2) and 1.1627 (O2), respectively. These results indicate that the process requires two excitation photons to produce a UC photon (twophoton absorption). And the slope approaching 1 may be due to the pumping saturation effect [33]. When the sample is irradiated with 405 nm light for 30s (LD, 200 mW), the reflection intensity is significantly reduced, as shown in Fig. 5a, b, and 5c. Three different absorption regions appear in the diffuse reflectance spectrum before illumination, including a broad band before 400 nm, a narrow peak region at about 450–665 nm, and a broad absorption region at about 700 nm. These absorption peaks in narrow peak region (450–665 nm)match the characteristic emission of Pr and Er ions. They originate mainly from the characteristic 4f–4f transitions of Pr3+ and Er3+ ions. Fig. 5d shows a reversible color irradiated with visible light (λ = 405 nm) and thermal stimulation coloring bleaching (230 °C for 10 min). It is found that samples sintered in different atmospheres exhibited different colors. The samples sintered in air are light green, the samples sintered in oxygen are dark green, and the samples sintered in nitrogen are light gray. Upon the 405 nm LD irradiation for 30 s, the color of the ceramic changes from initial color to grey immediately (air: light green → light grey; O2: dark green → dark grey; N2: light gray → light grey) [34]. According to previously reported results [35], Bi and Na elements would volatilize in large quantities during the sintering process, then giving rise to obvious green color. However, the ceramics sintered in nitrogen did not show green color, because the degree of Bi and Na volatilization would decrease due to the protection of nitrogen. When the colored sample was placed in a heating stage at a temperature of 230 °C, the dark gray quickly returned to the original color. So, the process of coloration by light irradiation and decoloration by heat stimulus can be completely repeated. Luminescence modulation, including modulation of light intensity, wave band and chromaticity, has attracted great interest due to their potential applications in electricity, magnetism, optics, and optoelectronics devices. As shown in Figs. 3 and 5, the UC and downshifting spectra of the samples sintered in 3 atmospheres overlap well with their reflectance spectra. It indicates that the interaction between luminescence and photochromism may occur, then resulting in luminescence quenching, as reported in some optical switching materials [36,37]. Therefore, this luminescent modulation and photochromic reaction can be considered as promising methods to achieve nondestructive readout
Photochromic behavior and mechanism of rare earth ion doped Na0.5Bi2.5Nb2O9 (NBN)-based ferroelectrics have been previously reported [23–25]. However, there is no clear evidence to prove the proposed mechanism. Therefore, we systematically investigated the photochromic behavior of NBN-based photochromic materials by controlling defects and traps under different sintering atmospheres. 2. Experimental Pr3+/Er3+ co-doped NBN ceramics were designed according to the formula of (Na0.5Bi0.5)0.96Er0.003Pr0.003Bi2Nb2O9 (NBN: Pr/Er), Raw materials of Na2CO3 (Alfa Aesar, Shanghai, China, 99.5%), Bi2O3(Alfa Aesar, 99.975%), Nb2O5 (Alfa Aesar, 99.5%), Pr6O11(Alfa Aesar, 99.9%)and Er2O3 (Alfa Aesar, 99.9%) were weighed and ball milled with ZrO2 balls in alcohol for 24 h. After drying at 80 °C for 6 h, the mixed powder was calcined at 900 °C for 4 h. All the powders were pressed into a disc sample of 12 mm in diameter and 1 mm in thickness, and sintered at 1100 °C for 2 h under air, O2 and N2 atmospheres. The phase structure of all samples was characterized by powder Xray diffraction (D8 Advanced, Bruker, Germany). Field emission scanning electron microscope (SEM, JSM-6510, JEOL, Tokyo, Japan) was used to observe the surface morphology. The diffuse reflectance spectrum was measured with an ultraviolet/visible spectrophotometer (U3900, Hitachi, Japan). The up-conversion emission spectrum at 980 nm excitation at room temperature was measured by a xenon lamp luminescence spectrometer. (F-4600 HITACHI, Tokyo, Japan). To achieve saturated coloration, the sample was irradiated with a 200 mW 405 nm laser diode (LD), the power density was about 4.12 mW/cm2. The chemical composition of samples and element binding energy were analyzed by monochromatic Al Kα (hν = 1486.6eV) radiation X-ray photoelectron spectroscopy (XPS) (VG, ESCALAB 250XI, Thermo Scientific, Surrey, UK). 3. Results and discussion Fig. 1 shows room-temperature X-ray diffraction patterns of NBN: Pr/Er ceramics in the 2θ range of 20°–60°sintered in different atmospheres. It is apparent that all diffraction peaks of samples can be well indexed to the layered perovskite Na0.5Bi2.5Nb2O9, and no obvious secondary phase is found. The strongest diffraction peak for NBN ceramic is (115), which is consistent with the (112 m + 1) highest diffraction peak in layer-structured ferroelectrics (BLSFs) reported in other articles [26]. The crystal structure observed in the [010] and [100] direction is shown in Fig. 1c. However, the diffraction peaks near the (115) slightly shift to higher angles with the change of sintering atmospheres from air, O2 to N2. These shifts can be attributed to the lattice distortion caused by the change of vacancies in the sample. Fig. 2 provides SEM images of the NBN: Pr/Er ceramics sintered at 1100 °C in different atmospheres. Well grown grains with dense microstructure and plate-like surface morphologies are obviously observed for all samples, showing typical Aurivillius feature due to its anisotropic behavior. It is noted that the average grain sizes show a slight change for samples sintered at air and O2 (Fig. 2a and b). Compared with grain sizes of the sample sintered at air and O2, the grain size at nitrogen significantly decreases, namely, the aspect ratio of L/T (length/thickness ratio) increases, as shown in Fig. 2c. These results indicate that the nitrogen sintering can effectively restrain the grain growth of NBN-based ceramics and induce the increase of the grain growth in the ab plane [27,28]. In Fig. 3a and b, we present the excitation spectra monitored by 613 nm and 550 nm and the photoluminescence (PL) spectra excited by 451 nm light of NBN: Pr/Er samples in different atmospheres at room temperature. When the monitoring wavelength is λem = 550 nm and λem = 613, the excitation spectra exhibit two different excitation modes. In Fig. 3b, the PL spectra exhibit a typical red emission located at 613 nm and green emission at 550 nm. The two emission peaks are 2
Journal of Luminescence 215 (2019) 116626
Y. Zhu, et al.
Fig. 1. (a) and(b) XRD patterns of the NBN: Pr/Er ceramics sintered in different atmospheres. (c) Crystal structure viewed along [010] and [100] directions.
decreased degree (ΔRt) before and after irradiation is obtained by the formula: ΔRt = (R0 – Rt)/R0 × 100%, where R0 and Rt are the red (613 nm) or green (550 nm) emission intensity at highest peak before and after light irradiation for 30 s. According to the calculation formula, the ΔRt values of NBN: Pr/Er samples sintered in different atmospheres are shown in Fig. 6b and d. Obviously, the ΔRt value of the sample sintered in nitrogen is smaller than the other 2 atmospheres. Inorganic photochromic materials should have high sensitivity, fast
and secure recording in practical applications of optical switches or data storage devices. Fig. 6 shows PL spectra and UC spectral changes of NBN: Er/Pr samples before and after 405 nm LD irradiation (200 mW) for 30 s. The PL spectra excited by 451 nm light and the UC spectra excited by 980 nm light. It is apparent that PL emission intensity and UC emission intensity of all samples is remarkably decreased, while the spectral shape and position after irradiation are unchanged (Fig. 6a and c). The
Fig. 2. SEM images for NBN: Er/Pr ceramics (a) sintered in air, (b) sintered in O2, (c) sintered in N2. 3
Journal of Luminescence 215 (2019) 116626
Y. Zhu, et al.
Fig. 3. (a)Excitation spectra monitored by 613 nm and 550 nm, (b) PL emission spectra in different atmospheres, (c) UC emission spectra of NBN: Er in different atmospheres, (d) The strongest emission intensities in the UC and PL spectrum in different atmospheres.
Fig. 4. UC emission spectra of samples with pump powers (a) sintered in air, (b) sintered in O2, (c) sintered in N2 and (d) the emission intensity versus pumping power curves.
Fig. 7a, the numbers “0123” were written by laser irradiation, and these numbers disappeared after the thermal stimulation. After re-irradiation, the numbers appeared again with clear numbers. This result shows that the material has good writing and erasing capabilities. In Fig. 7b, whether it is a solid five-pointed star pattern or a hollow five-pointed star pattern, it can be clearly expressed after light irradiation, indicating that the photochromic sensitivity of NBN ceramics is excellent. In
response time and excellent fatigue resistance in practical optical storage devices. In order to visually demonstrate the optical storage properties of NBN: Pr/Er ceramics, we have designed four different write and erase schemes. In order to obtain a more pronounced discoloration, NBN: Pr/Er ceramics are sintered in O2. The writing process is performed by a 405 nm laser according to the method shown in the figure, and the erasing is performed by means of thermal stimulation. In 4
Journal of Luminescence 215 (2019) 116626
Y. Zhu, et al.
Fig. 5. Reflectance spectra of NBN:Pr/Er sample before and after 405 nm light irradiation (a) sintered in air, (b) sintered in O2,(c) sintered in N2,(d)Photographs of NBN:Pr/Er ceramic samples before and after irradiation.
Fig. 7c, the five-pointed star patterns gradually became clear with the extension of the illumination time, and after 5s irradiation, the color would saturate, indicating that the response time of the material was rapid. Fig. 7d demonstrates the excellent fatigue resistance of the material through repeated irradiation and thermal stimulation. The “IMUST” (the name of the irradiation is the abbreviation of Inner Mongolia University of Science and Technology) letters are still clear after five cycles. These results demonstrate that NBN ceramics have broad application prospects in the optical storage fields.
In fact, the photochromism and the detail luminescence modulation process based on NBN-based materials have been reported in our previous results [38–40]. It is believed that some oxygen vacancies (VO.. ) would occur as a charge compensation due to the volatilization of alkali metal Na and Bi elements, during high-temperature sintering process. When the sample is irradiated with light (405 nm, 200 mW), the electrons in the valence band will transform into conductive bands or defect levels, these electrons are captured by oxygen vacancies in a short time. Subsequently, the signal light intensity irradiating into the samples Fig. 6. PL spectral and UC spectral changes of NBN: Er/Pr samples before and after 405 nm light irradiation. (a) PL spectra changes of the NBN: Er/Pr samples with different atmospheres before and after irradiation excited by 451 nm, (b) The calculated ΔRt values at 550 nm and 613 nm with different atmospheres. (c) UC spectra changes of the NBN: Er/Pr samples with different atmospheres before and after irradiation excited by 980 nm, (d) The calculated ΔRt values at 550 nm with different atmospheres.
5
Journal of Luminescence 215 (2019) 116626
Y. Zhu, et al.
Fig. 7. Demonstration experiments for optical storage characteristics of NBN ceramics, (a) writing and erasing experiments of numbers “0123”, (b) radiation experiments of solid and hollow pentagonal stars, (c) pentagonal star patterns irradiated at different time, (d) writing and erasing cycle test of the letter “IMUST”.
would decrease, then leading to the darkened surface of the samples (pale gray) and the decreased reflective spectra intensity. Under thermal stimulus, oxygen vacancies bound electrons are released, resulting in the disappearance of color centers, the color of the ceramic returns to its original state. Therefore, the formation of the color center is the cause of the color change. Color center would be formed by the VO.. in NBN ceramic. For ceramics sintered in three different atmospheres, the formation of color centers is mainly coming from O vacancies induced by the volatilization of alkali metal ions at A site and the high temperature and low oxygen partial pressure (as shown in Equations (1)–(3)) [41]. But, why is the ΔRt of samples sintered in N2 far lower than that sintered in air and O2? We believe that due to the protective effect of N2, the volatilization of Bi and Na in N2 is much lower than that in O2 and air, as shown in Fig. 8. Although a certain amount of VO.. can be generated under high temperature and low oxygen partial pressure, it is not dominant, and its quantity is much lower than the amount of VO.. generated by the volatilization of Bi and Na in the other 2 atm. As a result, the VO.. contents of sintered samples in N2 is much less than that of sintered samples in the other 2 atm. The decrease of VO.. in samples leads to the decrease of color centers of sintered samples in N2. Therefore, the relative intensity of sintered samples in N2 is much lower than that of sintered samples in O2
and air [42,43]. The formation of O vacancies can be further verified by XPS spectral analysis.
* + 3OO* 2BiBi
high temperature ′ ′′ + 3VO.. + Bi2 O3 ( ↑ ) → 2VBi
(1)
* + OO* 2NaNa
high temperature ′ + VO.. + Na2 O ( ↑ ) → 2VNa
(2)
OO*
high temperature → VO.. + 1/2O2 ( ↑ )
(3)
The XPS spectra and the fitting O 1s spectra of the samples sintered in different atmospheres before irradiation are shown in Fig. 9, and the fitting data are listed in Table 1. It is found that the lattice oxygen peaks representing the Nb–O and A−O bonds are often accompanied by shoulder peaks. Due to the presence of oxygen vacancies, shoulder peaks are usually assigned to absorbed oxygen [44]. Moreover, it can be seen that lattice oxygen peaks and the absorption oxygen peaks do not show significant shift. It is well known that the ratio of the fitting area of lattice oxygen to absorbed oxygen (Vo/O2−) can indicate the VO.. content in ceramic samples. From Table 1, the Vo/O2− value of the sample sintered in N2 (0.43) is obviously lower than that sintered in O2 (0.86) and air (0.57), suggesting that the VO.. content of samples sintered in N2 is the lowest, while the VO.. content of samples sintered in O2 is the 6
Journal of Luminescence 215 (2019) 116626
Y. Zhu, et al.
Fig. 8. Volatilization process of Bi/Na during sintering in different atmospheres.
highest. This is consistent with our test results. In fact, a small amount of VO.. will be filled when sintered in O2, but the value of VO.. caused by the large amount of K and Na volatilization is much larger than the value of the VO.. that are filled. Therefore, the VO.. content in O2 is much higher than the VO.. content in the other 2 atm. According to the relevant literature [45,46], the oxygen vacancies can be used as effective sensitizers for the adjacent rare earth ions to enhance the PL intensity. Therefore, we speculate that oxygen vacancies in NBN matrix can also be used as effective sensitizers for Pr and Er ions. The oxygen vacancies transferred excitation energy to the adjacent rare earth ion sites and thus greatly enhanced PL and UC luminescence intensity of the sample (this process is schematically illustrated in Fig. 10). Based on the XPS results of the VO.. content of samples sintered in N2, we believe that O vacancy change is the main reason for the decreased upconversion and downshifting emission intensities for samples sintered in N2.
Table 1 Fitting parameters of the O 1s XPS spectra of Er doped NBN samples in different atmospheres. Samples
Lattice O (O2−)
Absorbed O (*Vo)
Vo/O2--
Air O2 N2
529.20 eV 529.02 eV 529.27 eV
531.29 eV 531.10 eV 531.83 eV
0.57 0.86 0.43
*Vo means O vacancy.
4. Conclusions Pr3+ and Er3+ co-doped NBN ceramics have been prepared by a conventional solid-state sintering method in air, O2 and N2 atmospheres. Their photoluminescence, upconversion luminescence,
Fig. 9. (a) XPS spectra of NBN sample and O 1s spectra for NBN:0.01Er before irradiation (b) sintered in air, (c) sintered in O2, (d) sintered in N2. 7
Journal of Luminescence 215 (2019) 116626
Y. Zhu, et al.
Fig. 10. The schematic diagram of the energy transfer process mediated by O vacancy. [10] S. Kamimura, H. Yamada, C.N. Xu, Purple photochromism in Sr2SnO4:Eu3+ with layered perovskite-related structure, Appl. Phys. Lett. 102 (2013) 363. [11] Y. Li, Y. Wang, Y. Gong, X. Xu, F. Zhang, Photoionization behavior of Eu2+-doped BaMgSiO4 long-persisting phosphor upon UV irradiation, Acta Mater. 59 (2011) 3174–3183. [12] H.E. Moll, A. Dolbecq, I.M. Mbomekalle, J. Marrot, P. Deniard, R. Dessapt, P. Mialane, Tuning the photochromic properties of molybdenum bisphosphonate polyoxometalates, Inorg. Chem. 51 (2012) 2291–2302. [13] C. Xu, J. Zhang, L. Xu, H. Zhao, Mechanism of photochromic effect in Pb (Zr,Ti) O3 and (Pb,La) (Zr,Ti) O3 ceramics under violet/infrared light illumination, J. Appl. Phys. 117 (2015) 023107. [14] E. Orgiu, P. Samori, 25th anniversary article: organic electronics marries photochromism: generation of multifunctional interfaces, materials, and devices, Adv. Mater. 26 (2014) 1827–1845. [15] M.S. Wang, G. Xu, Z.J. Zhang, G.C. Guo, Inorganic–organic hybrid photochromic materials, Chem. Commun. 46 (2010) 361–376. [16] S.K. Deb, Optical and photoelectric properties and colour centres in thin films of tungsten oxide, Philos. Mag. 27 (1973) 801–822. [17] B.W. Faughnan, R.S. Crandall, M.A. Lampert, Model for the bleaching of WO3 electrochromic films by an electric field, Phys. Rev. Lett. 27 (1975) 275–277. [18] O.F. Schirmer, V. Wittwer, G. Baur, G. Brandt, Dependence of WO3 electrochromic absorption on crystallinity, J. Electrochem. Soc. 124 (1977) 749–753. [19] T. He, J. Yao, Photochromic materials based on tungsten oxide, J. Mater. Chem. 17 (2007) 4547–4557. [20] Y. Wei, Z. Wu, Y. Jia, J. Wu, Y. Shen, H. Luo, Dual-enhancement of ferro-/piezoelectric and photoluminescent performance in Pr3+ doped (K0.5Na0.5) NbO3 leadfree ceramics, Appl. Phys. Lett. 105 (2014) 042902. [21] X. Wang, C.N. Xu, H. Yamada, K. Nishikubo, X.‐G. Zheng, Electro-mechano-optical conversions in Pr3+-doped BaTiO3-CaTiO3, Adv. Mater. 17 (2005) 1254–1258. [22] P. Du, L. Luo, W. Li, Q. Yue, Upconversion emission in Er-doped and Er/Yb-codoped ferroelectric Na0.5Bi0.5TiO3 and its temperature sensing application, J. Appl. Phys. 116 (2014) 014102. [23] Q.W. Zhang, Y. Zhang, H.Q. Sun, W. Geng, X.S. Wang, X.H. Hao, S. L, An, Tunable luminescence contrast of Na0.5Bi4.5Ti4O15: Re (Re=Sm, Pr, Er) photochromics by controlling the excitation energy of luminescent centers, ACS Appl. Mater. Interfaces 8 (2016) 34581–34589. [24] Q.W. Zhang, Y. Zhang, H.Q. Sun, Q. S, X.S. Wang, X.H. Hao, S.L., An, Photoluminescence, photochromism, and reversible luminescence modulation behavior of Sm-doped Na0.5 Bi2.5Nb2O9ferroelectrics, J. Eur. Ceram. Soc. 37 (2017) 955–966. [25] Q.W. Zhang, S.S. Yue, Y. Zhang, H.Q. Sun, X.S. Wang, X.H. Hao, S. L, An, Nondestructive up-conversion readout in Er/Yb co-doped Na0.5Bi2.5Nb2O9-based optical storage materials for optical data storage device applications, J. Mater. Chem. C 5 (2017) 3838–3847. [26] Z.Y. Zhou, Y.C. Li, S.P. Hui, X.L. Dong, Effect of tungsten doping in bismuth-layered Na0.5Bi2.5Nb2O9 high temperature piezoceramics, Appl. Phys. Lett. 104 (2014) 166. [27] C.B. Long, H.Q. Fan, M.M. Li, Q. Li, Crystal structure and enhanced piezoelectric properties of scandium and bismuth-excess modified Aurivillius oxides, Na0.5xBi2.5+xNb2- xScxO9, Eur. J. Inorg. Chem. 32 (2013) 5622–5630. [28] C.B. Long, H.Q. Fan, P.R. Ren, Structure, phase transition behaviors and electrical properties of Nd substituted Aurivillius polycrystallines Na0.5NdxBi2.5-x Nb2O9 (x= 0.1, 0.2, 0.3, and 0.5), Inorg. Chem. 52 (2013) 5045–5054. [29] X. Wu, S.B. Lu, K.W. Kwok, Photoluminescence, electro-optic response and piezoelectric properties in pressureless-sintered Er-doped KNN-based transparent ceramics, J. Alloy. Comp. 695 (2017) 3573–3578. [30] F. Vetrone, J.C. Boyer, J.A. Capobianco, Significance of Yb3+ concentration on the upconversion mechanisms in codoped Y2O3: Er3+, Yb3+ nanocrystals, J. Appl. Phys. 96 (2004) 661–667. [31] S. Chen, M. Wu, L.Q. An, Y.X. Li, S.W. Wang, Strong green and red upconversion emission in Er3+-doped Na1/2Bi1/2TiO3 ceramics, J. Am. Ceram. Soc. 90 (2007) 664–666. [32] H.Q. Sun, Q.W. Zhang, X.S. Wang, M. Gu, Green and red upconversion
photochromism and luminescence modulation properties are systematically investigated. During the course of the study, the samples are found to exhibit excellent multi-color luminescence (red-green), multimode (upconversion/downshifting) luminescence properties. The experimental results show that the samples sintered in air and oxygen are light green and dark green, while the green of the samples sintered in nitrogen disappears. It is worth noting that the sample sintered in N2 at 405 nm has luminescence switching contrast (ΔRt) that is significantly lower than the ΔRt values under air and O2, and the upconversion and downshifting emission intensities are significantly decreased. XPS analysis confirmed that the change of emission intensities and ΔRt value was closely related to defects and traps caused by volatilization of Bi and Na in different atmospheres. Acknowledgment This work was supported by the Natural Science Foundation of China (No. 51562030, 51802164), the Natural Science Foundation of Inner Mongolia (No. 2018JQ06), Program for Young Talents of Science and Technology in Universities of Inner Mongolia Autonomous Region (NJYT-17-A10, NJYT-17-B09), Young Academic Core Program of Inner Mongolia University of Science and Technology (No. 2016YQL01), and the Program for Innovative Research Team in Universities of Inner Mongolia Autonomous Region (NMGIRT-A1605). References [1] R. Pardo, M. Zayat, D. Levy, Photochromic organic–inorganic hybrid materials, Chem. Soc. Rev. 40 (2011) 672–687. [2] H. Tao, J. Yao, Photochromism in composite and hybrid materials based on transition-metal oxides and polyoxometalates, Prog. Mater. Sci. 51 (2006) 810–879. [3] B.A. Reinhardt, L.L. Brott, S.J. Clarson, A.G. Dillard, J.C. Bhatt, R. Kannan, L.X. Yuan, G.S. He, P.N. Prasad, Highly active two-photon Dyes: design, synthesis, and characterization toward application, Chem. Mater. 10 (1998) 1863–1874. [4] L. Ding, L.W. Chung, K. Morokuma, Reaction mechanism of photoinduced decarboxylation of the photoactivatable green fluorescent protein: an ONIOM (QM:MM) study, J. Phys. Chem. C 117 (2013) 1075. [5] J. Boixel, Y.F. Zhu, H.L. Bozec, M.A. Benmensour, A. Boucekkine, K.M. Wong, A. Colombo, D. Roberto, V. Guerchais, D. Jacquemin, Contrasted photochromic and luminescent properties in dinuclear Pt(ii) complexes linked through a central dithienylethene unit, Chem. Commun. 52 (2016) 9833–9836. [6] H.B. Cheng, G.F. Hu, Z.H. Zhang, L. Gao, X.F. Gao, H.C. Wu, Photocontrolled reversible luminescent lanthanide molecular switch based on a diarylethene-europium dyad, Inorg. Chem. 55 (2016) 7962–7968. [7] B.W. Faughnan, Z.J. Kiss, Photoinduced reversible charge-transfer processes in transition-metal-doped single-crystal SrTiO3 and TiO2, Phys. Rev. Lett. 21 (1968) 1331. [8] K. Ajito, L.A. Nagahara, D.A. Tryk, K. Hashimoto, A. Fujishima, Study of the photochromic properties of amorphous MoO3 films using Raman microscopy, J. Phys. Chem. 99 (1995) 16383–16388. [9] C.S. Blackman, I.P. Parkin, Atmospheric pressure chemical vapor deposition of crystalline monoclinic WO3 and WO3-x thin films from reaction of WCl6 with Ocontaining solvents and their photochromic and electrochromic properties, Chem. Mater. 17 (2005) 1583–1590.
8
Journal of Luminescence 215 (2019) 116626
Y. Zhu, et al.
[33]
[34]
[35]
[36]
[37] [38]
[39]
luminescence of Er3+ -doped K0.5Na0.5NbO3 ceramics, Ceram. Int. 40 (2014) 2581–2584. Z. Pan, S.H. Morgan, A. Loper, V. King, B.H. Long, W. E, Collins Infrared to visible upconversion in Er3+-doped-lead-germanate glass: effects of Er3+ ion concentration, J. Appl. Phys. 77 (1995) 4688–4692. C. Xu, J. Zhang, L. Xu, H. Zhao, Mechanism of photochromic effect in Pb(Zr,Ti) O3 and (Pb,La) (Zr,Ti) O3 ceramics under violet/infrared light illumination, J. Appl. Phys. 117 (2015) 023107. H.Q. Sun, J. Liu, X.S. Wang, Q.W. Zhang, X.H. Hao, S.L. An, (K,Na)NbO3 ferroelectrics: a new class of solid-state photochromic materials with reversible luminescence switching behavior, J. Mater. Chem. C 5 (2017) 9080–9087. Y. Zhuang, J. Ueda, S. Tanabe, Photochromism and white long-lasting persistent luminescence in Bi3+-doped ZnGa2O4 ceramics, Opt. Mater. Express 2 (2012) 1378–1383. F.M. Raymo, M. Tomasulo, Fluorescence modulation with photochromic switches, J. Phys. Chem. A 109 (2005) 7343–7352. Y. Zhang, J. Liu, H.Q. Sun, D.F. Peng, R.H. Li, C. Bulin, X.S. Wang, Q.W. Zhang, X.H. Hao, Reversible luminescence modulation of Ho-doped K0.5Na0.5NbO3 piezoelectrics with high luminescence contrast, J. Am. Ceram. Soc. 101 (2017) 2305–2312. Q.W. Zhang, H.Q. Sun, X.S. Wang, X.H. Hao, S.L. An, Reversible luminescence modulation upon photochromic reactions in rare-earth doped ferroelectric oxides by in situ photoluminescence spectroscopy, ACS Appl. Mater. Interfaces 7 (2015)
25289–25297. [40] Q.W. Zhang, X.W. Zheng, H.Q. Sun, W.Q. Li, X.S. Wang, X.H. Hao, S. L, An, dualmode luminescence modulation upon visible-light-driven photochromism with high contrast for inorganic luminescence ferroelectrics, ACS Appl. Mater. Interfaces 8 (2016) 4789–4794. [41] J.S. Hong, Y.H. Huang, Y.J. Wu, M.S. Fu, J. Li, X.Q. Liu, Oxygen-vacancy-induced reversible control of ferroelectric polarization in Ba4Eu2Fe2Nb8O30 ceramics, J. Appl. Phys. 124 (2018) 064105. [42] Z.Y. Cen, X.H. Wang, Y. Huan, Y.C. Zhen, W. Feng, L.T. Li, Defect engineering on phase structure and temperature stability of KNN-based ceramics sintered in different atmospheres, J. Am. Ceram. Soc. 101 (2018) 3032–3043. [43] H.C. Thong, Q. Li, M.H. Zhang, C.L. Zhao, K.X. Huang, J.F. Li, K. Wang, Defect suppression in CaZrO3-modified (K,Na)NbO3-based lead-free piezoceramic by sintering atmosphere control, J. Am. Ceram. Soc. 101 (2018) 3393–3401. [44] T. Saitoh, Electronic structure of La1-xSrxMnO3 studied by photoemission and x-rayabsorption spectroscopy, Phys. Rev. B 51 (1995) 13942–13951. [45] Y.Z. Xie, Z.W. Ma, L.X. Liu, Y.R. Su, H.T. Zhao, Y.X. Liu, Z.X. Zhang, H.G. Duan, J. Li, E.Q. Xie, Oxygen defects-modulated green photoluminescence of Tb-doped ZrO2 nanofibers, Appl. Phys. Lett. 97 (2010) 141916. [46] S. Kim, S.J. Rhee, D.A. Turnbull, E.E. Reuter, X. Li, J.J. Coleman, S. G, Bishop Observation of multiple Er3+ sites in Er-implanted GaN by site-selective photoluminescence excitation spectroscopy, Appl. Phys. Lett. 71 (1997) 231–233.
9
Contents lists available at ScienceDirect
Journal of Luminescence journal homepage: www.elsevier.com/locate/jlumin
Defect modulated luminescent and photochromic behaviors in Pr/Er codoped Na0.5Bi2.5Nb2O9 ceramics for display and optical storage
T
Yan Zhua, Yang Lva, Yunhui Xiaoa, Haiqin Suna,*, Qiwei Zhanga,b,**, Xihong Haoa,b a
Inner Mongolia Key Laboratory of Ferroelectric-related New Energy Materials and Devices, School of Materials and Metallurgy, Inner Mongolia University of Science and Technology, 7# Arding Street, Kun District, Baotou, 014010, China b Key Laboratory of Integrated Exploitation of Bayan Obo Multi-Metal Resources, Inner Mongolia University of Science and Technology, Baotou, 014010, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Multi-color luminescence Luminescence modulation Photochromism Defects
In order to explore the mechanism of luminescence modulation and photochromism of Na0.5Bi2.5Nb2O9 (NBN)based photochromic materials, the luminescence, photochromism and luminescence modulation properties of Pr3+/Er3+ co-doped NBN ceramics under different sintering atmospheres (Air, O2, and N2) were systematically studied. The results show that the samples exhibit excellent properties of multi-color luminescence (red-green), multi-mode (upconversion/downshifting) luminescence properties. Correspondingly, the upconversion and downshifting emission intensities are significantly decreased for samples sintered at nitrogen. And, the luminescence switching contrast (ΔRt) of the sample sintered in N2 is also obviously lower than the ΔRt values under air and O2 atmospheres upon 405 nm irradiation. Such color and ΔRt value changes under different atmospheres are closely related to defects and traps due to Bi and Na element volatilizations, which are well verified by XPS analysis. Meanwhile, various pattern displays based on photochromic NBN materials can be well achieved with fast response and good fatigue resistance.
1. Introduction Solid-state photochromic compounds (organic and inorganic photochromic materials) have been always considered as a promising material for optical storage, photo-switching, and sensors because of their high sensitivity, fast response time, and excellent fatigue resistance [1–3]. To date, the studies of organic photochromic phenomenon are extensively explored, for example, a dyad composed of photochromic and luminescent dye units, small organic molecules, photoactivatable luminescent proteins (PAFPs), metal complexes with photochromic units, photochromic bisthienylethene and diarylethene (DAET) derivatives, etc [4–6]. However, photochromism of inorganic compounds have rarely been reported. From the earliest study of the photochromic behavior of transition metal-doped SrTiO3 by Faughnan et al., in 1968 [7], the exploration of inorganic photochromism materials has never stopped. Nowadays, many inorganic materials (WO3, TiO2, Pb(Zr,Ti)O3, Sr2SnO4: Eu, BaMgSiO4: Eu, polyoxometalates etc.) have been found to have excellent photochromic properties [8–13]. Compared to the organic photochromic materials, inorganic photochromic materials have many distinct advantages: (i) excellent mechanical strength; (ii) high
thermal stability; and (iii) good chemical stability [14]. Moreover, inorganic photochromic materials are indispensable in high-density optical memories and 3D graphics memory devices [15]. Currently, there are several theoretical models to explain photochromic behavior. For inorganic photochromic materials, the model is mainly based on the presence of color centers or hydrogen bronze under irradiation, and significant changes in the absorption spectrum are thought to be caused by color centers, intervanlence-charge transfer (IVCT), or small-polaron transitions [16–18]. For some polycrystalline or nanocrystalline materials, light absorption is primarily coming from free carriers or trapped carriers [19]. However, these two mechanisms are in principle difficult to achieve non-destructive illuminating readout capabilities, hindering their use in optical memory and switching applications. Recently, luminescent materials based on ferroelectric perovskite compounds have been extensively studied for their potential applications in integrated optoelectronic devices [20–22]. Due to the distinct structure of perovskite-type ferroelectrics, it may involve completely different luminescence modulation mechanisms, and its inherent ferro-/piezoelectric properties have great application value in the field of photochromic and multi-functional devices.
*
Corresponding author. Corresponding author. Key Laboratory of Integrated Exploitation of Bayan Obo Multi-Metal Resources, Inner Mongolia University of Science and Technology, Baotou, 014010, China. E-mail addresses: [email protected] (H. Sun), [email protected] (Q. Zhang). **
https://doi.org/10.1016/j.jlumin.2019.116626 Received 27 May 2019; Received in revised form 9 July 2019; Accepted 13 July 2019 Available online 14 July 2019 0022-2313/ © 2019 Elsevier B.V. All rights reserved.
Journal of Luminescence 215 (2019) 116626
Y. Zhu, et al.
apparently attributed to the characteristic emission of Pr3+ and Er3+ ions. It is found that the combination of Pr3+ and Er3+ ions can exhibit excellent multi-color luminescence (red-green), multi-mode (upconversion/downshifting) luminescence properties. Fig. 3c shows the upconversion (UC) emission spectra of Pr3+/Er3+ co-doped NBN ceramics excited by 980 nm light, there are three emission bands: green emissions in 520–539 nm and 539–570 nm, and a weak red emission in 650–680 nm, which are attributed to the intra 4f–4f electronic transitions of 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 of Er3+, respectively. All emission bands are consistent with those reported by other groups [29–31]. Further, the green emission intensity is significantly stronger than the red emission intensity. Fig. 3d provides the intensity of the highest peak in UC and PL spectrum in different atmospheres. It can be seen that the UC and PL luminescence intensity of sample sintered in O2 is the strongest, obviously higher than that sintered in N2. Fig. 4 shows the UC emission spectra of samples sintered in different atmospheres with pump powers of 20–400 mW and the emission intensity vs. pumping power curves. It can be seen that the UC emission intensity increases with the increase of pump powers. In order to investigate UC mechanisms and photon absorption processes, the number of photons can be calculated according to the relationship between UC emission intensity (Iup) and incident pumping power (P), and UC emission intensity Iup is approximately proportional to the pumping power (P): I ∝ Pn [32], where n is the number of photons involved in the pumping mechanism. The obtained n values are 1.0566 (Air),1.0668 (N2) and 1.1627 (O2), respectively. These results indicate that the process requires two excitation photons to produce a UC photon (twophoton absorption). And the slope approaching 1 may be due to the pumping saturation effect [33]. When the sample is irradiated with 405 nm light for 30s (LD, 200 mW), the reflection intensity is significantly reduced, as shown in Fig. 5a, b, and 5c. Three different absorption regions appear in the diffuse reflectance spectrum before illumination, including a broad band before 400 nm, a narrow peak region at about 450–665 nm, and a broad absorption region at about 700 nm. These absorption peaks in narrow peak region (450–665 nm)match the characteristic emission of Pr and Er ions. They originate mainly from the characteristic 4f–4f transitions of Pr3+ and Er3+ ions. Fig. 5d shows a reversible color irradiated with visible light (λ = 405 nm) and thermal stimulation coloring bleaching (230 °C for 10 min). It is found that samples sintered in different atmospheres exhibited different colors. The samples sintered in air are light green, the samples sintered in oxygen are dark green, and the samples sintered in nitrogen are light gray. Upon the 405 nm LD irradiation for 30 s, the color of the ceramic changes from initial color to grey immediately (air: light green → light grey; O2: dark green → dark grey; N2: light gray → light grey) [34]. According to previously reported results [35], Bi and Na elements would volatilize in large quantities during the sintering process, then giving rise to obvious green color. However, the ceramics sintered in nitrogen did not show green color, because the degree of Bi and Na volatilization would decrease due to the protection of nitrogen. When the colored sample was placed in a heating stage at a temperature of 230 °C, the dark gray quickly returned to the original color. So, the process of coloration by light irradiation and decoloration by heat stimulus can be completely repeated. Luminescence modulation, including modulation of light intensity, wave band and chromaticity, has attracted great interest due to their potential applications in electricity, magnetism, optics, and optoelectronics devices. As shown in Figs. 3 and 5, the UC and downshifting spectra of the samples sintered in 3 atmospheres overlap well with their reflectance spectra. It indicates that the interaction between luminescence and photochromism may occur, then resulting in luminescence quenching, as reported in some optical switching materials [36,37]. Therefore, this luminescent modulation and photochromic reaction can be considered as promising methods to achieve nondestructive readout
Photochromic behavior and mechanism of rare earth ion doped Na0.5Bi2.5Nb2O9 (NBN)-based ferroelectrics have been previously reported [23–25]. However, there is no clear evidence to prove the proposed mechanism. Therefore, we systematically investigated the photochromic behavior of NBN-based photochromic materials by controlling defects and traps under different sintering atmospheres. 2. Experimental Pr3+/Er3+ co-doped NBN ceramics were designed according to the formula of (Na0.5Bi0.5)0.96Er0.003Pr0.003Bi2Nb2O9 (NBN: Pr/Er), Raw materials of Na2CO3 (Alfa Aesar, Shanghai, China, 99.5%), Bi2O3(Alfa Aesar, 99.975%), Nb2O5 (Alfa Aesar, 99.5%), Pr6O11(Alfa Aesar, 99.9%)and Er2O3 (Alfa Aesar, 99.9%) were weighed and ball milled with ZrO2 balls in alcohol for 24 h. After drying at 80 °C for 6 h, the mixed powder was calcined at 900 °C for 4 h. All the powders were pressed into a disc sample of 12 mm in diameter and 1 mm in thickness, and sintered at 1100 °C for 2 h under air, O2 and N2 atmospheres. The phase structure of all samples was characterized by powder Xray diffraction (D8 Advanced, Bruker, Germany). Field emission scanning electron microscope (SEM, JSM-6510, JEOL, Tokyo, Japan) was used to observe the surface morphology. The diffuse reflectance spectrum was measured with an ultraviolet/visible spectrophotometer (U3900, Hitachi, Japan). The up-conversion emission spectrum at 980 nm excitation at room temperature was measured by a xenon lamp luminescence spectrometer. (F-4600 HITACHI, Tokyo, Japan). To achieve saturated coloration, the sample was irradiated with a 200 mW 405 nm laser diode (LD), the power density was about 4.12 mW/cm2. The chemical composition of samples and element binding energy were analyzed by monochromatic Al Kα (hν = 1486.6eV) radiation X-ray photoelectron spectroscopy (XPS) (VG, ESCALAB 250XI, Thermo Scientific, Surrey, UK). 3. Results and discussion Fig. 1 shows room-temperature X-ray diffraction patterns of NBN: Pr/Er ceramics in the 2θ range of 20°–60°sintered in different atmospheres. It is apparent that all diffraction peaks of samples can be well indexed to the layered perovskite Na0.5Bi2.5Nb2O9, and no obvious secondary phase is found. The strongest diffraction peak for NBN ceramic is (115), which is consistent with the (112 m + 1) highest diffraction peak in layer-structured ferroelectrics (BLSFs) reported in other articles [26]. The crystal structure observed in the [010] and [100] direction is shown in Fig. 1c. However, the diffraction peaks near the (115) slightly shift to higher angles with the change of sintering atmospheres from air, O2 to N2. These shifts can be attributed to the lattice distortion caused by the change of vacancies in the sample. Fig. 2 provides SEM images of the NBN: Pr/Er ceramics sintered at 1100 °C in different atmospheres. Well grown grains with dense microstructure and plate-like surface morphologies are obviously observed for all samples, showing typical Aurivillius feature due to its anisotropic behavior. It is noted that the average grain sizes show a slight change for samples sintered at air and O2 (Fig. 2a and b). Compared with grain sizes of the sample sintered at air and O2, the grain size at nitrogen significantly decreases, namely, the aspect ratio of L/T (length/thickness ratio) increases, as shown in Fig. 2c. These results indicate that the nitrogen sintering can effectively restrain the grain growth of NBN-based ceramics and induce the increase of the grain growth in the ab plane [27,28]. In Fig. 3a and b, we present the excitation spectra monitored by 613 nm and 550 nm and the photoluminescence (PL) spectra excited by 451 nm light of NBN: Pr/Er samples in different atmospheres at room temperature. When the monitoring wavelength is λem = 550 nm and λem = 613, the excitation spectra exhibit two different excitation modes. In Fig. 3b, the PL spectra exhibit a typical red emission located at 613 nm and green emission at 550 nm. The two emission peaks are 2
Journal of Luminescence 215 (2019) 116626
Y. Zhu, et al.
Fig. 1. (a) and(b) XRD patterns of the NBN: Pr/Er ceramics sintered in different atmospheres. (c) Crystal structure viewed along [010] and [100] directions.
decreased degree (ΔRt) before and after irradiation is obtained by the formula: ΔRt = (R0 – Rt)/R0 × 100%, where R0 and Rt are the red (613 nm) or green (550 nm) emission intensity at highest peak before and after light irradiation for 30 s. According to the calculation formula, the ΔRt values of NBN: Pr/Er samples sintered in different atmospheres are shown in Fig. 6b and d. Obviously, the ΔRt value of the sample sintered in nitrogen is smaller than the other 2 atmospheres. Inorganic photochromic materials should have high sensitivity, fast
and secure recording in practical applications of optical switches or data storage devices. Fig. 6 shows PL spectra and UC spectral changes of NBN: Er/Pr samples before and after 405 nm LD irradiation (200 mW) for 30 s. The PL spectra excited by 451 nm light and the UC spectra excited by 980 nm light. It is apparent that PL emission intensity and UC emission intensity of all samples is remarkably decreased, while the spectral shape and position after irradiation are unchanged (Fig. 6a and c). The
Fig. 2. SEM images for NBN: Er/Pr ceramics (a) sintered in air, (b) sintered in O2, (c) sintered in N2. 3
Journal of Luminescence 215 (2019) 116626
Y. Zhu, et al.
Fig. 3. (a)Excitation spectra monitored by 613 nm and 550 nm, (b) PL emission spectra in different atmospheres, (c) UC emission spectra of NBN: Er in different atmospheres, (d) The strongest emission intensities in the UC and PL spectrum in different atmospheres.
Fig. 4. UC emission spectra of samples with pump powers (a) sintered in air, (b) sintered in O2, (c) sintered in N2 and (d) the emission intensity versus pumping power curves.
Fig. 7a, the numbers “0123” were written by laser irradiation, and these numbers disappeared after the thermal stimulation. After re-irradiation, the numbers appeared again with clear numbers. This result shows that the material has good writing and erasing capabilities. In Fig. 7b, whether it is a solid five-pointed star pattern or a hollow five-pointed star pattern, it can be clearly expressed after light irradiation, indicating that the photochromic sensitivity of NBN ceramics is excellent. In
response time and excellent fatigue resistance in practical optical storage devices. In order to visually demonstrate the optical storage properties of NBN: Pr/Er ceramics, we have designed four different write and erase schemes. In order to obtain a more pronounced discoloration, NBN: Pr/Er ceramics are sintered in O2. The writing process is performed by a 405 nm laser according to the method shown in the figure, and the erasing is performed by means of thermal stimulation. In 4
Journal of Luminescence 215 (2019) 116626
Y. Zhu, et al.
Fig. 5. Reflectance spectra of NBN:Pr/Er sample before and after 405 nm light irradiation (a) sintered in air, (b) sintered in O2,(c) sintered in N2,(d)Photographs of NBN:Pr/Er ceramic samples before and after irradiation.
Fig. 7c, the five-pointed star patterns gradually became clear with the extension of the illumination time, and after 5s irradiation, the color would saturate, indicating that the response time of the material was rapid. Fig. 7d demonstrates the excellent fatigue resistance of the material through repeated irradiation and thermal stimulation. The “IMUST” (the name of the irradiation is the abbreviation of Inner Mongolia University of Science and Technology) letters are still clear after five cycles. These results demonstrate that NBN ceramics have broad application prospects in the optical storage fields.
In fact, the photochromism and the detail luminescence modulation process based on NBN-based materials have been reported in our previous results [38–40]. It is believed that some oxygen vacancies (VO.. ) would occur as a charge compensation due to the volatilization of alkali metal Na and Bi elements, during high-temperature sintering process. When the sample is irradiated with light (405 nm, 200 mW), the electrons in the valence band will transform into conductive bands or defect levels, these electrons are captured by oxygen vacancies in a short time. Subsequently, the signal light intensity irradiating into the samples Fig. 6. PL spectral and UC spectral changes of NBN: Er/Pr samples before and after 405 nm light irradiation. (a) PL spectra changes of the NBN: Er/Pr samples with different atmospheres before and after irradiation excited by 451 nm, (b) The calculated ΔRt values at 550 nm and 613 nm with different atmospheres. (c) UC spectra changes of the NBN: Er/Pr samples with different atmospheres before and after irradiation excited by 980 nm, (d) The calculated ΔRt values at 550 nm with different atmospheres.
5
Journal of Luminescence 215 (2019) 116626
Y. Zhu, et al.
Fig. 7. Demonstration experiments for optical storage characteristics of NBN ceramics, (a) writing and erasing experiments of numbers “0123”, (b) radiation experiments of solid and hollow pentagonal stars, (c) pentagonal star patterns irradiated at different time, (d) writing and erasing cycle test of the letter “IMUST”.
would decrease, then leading to the darkened surface of the samples (pale gray) and the decreased reflective spectra intensity. Under thermal stimulus, oxygen vacancies bound electrons are released, resulting in the disappearance of color centers, the color of the ceramic returns to its original state. Therefore, the formation of the color center is the cause of the color change. Color center would be formed by the VO.. in NBN ceramic. For ceramics sintered in three different atmospheres, the formation of color centers is mainly coming from O vacancies induced by the volatilization of alkali metal ions at A site and the high temperature and low oxygen partial pressure (as shown in Equations (1)–(3)) [41]. But, why is the ΔRt of samples sintered in N2 far lower than that sintered in air and O2? We believe that due to the protective effect of N2, the volatilization of Bi and Na in N2 is much lower than that in O2 and air, as shown in Fig. 8. Although a certain amount of VO.. can be generated under high temperature and low oxygen partial pressure, it is not dominant, and its quantity is much lower than the amount of VO.. generated by the volatilization of Bi and Na in the other 2 atm. As a result, the VO.. contents of sintered samples in N2 is much less than that of sintered samples in the other 2 atm. The decrease of VO.. in samples leads to the decrease of color centers of sintered samples in N2. Therefore, the relative intensity of sintered samples in N2 is much lower than that of sintered samples in O2
and air [42,43]. The formation of O vacancies can be further verified by XPS spectral analysis.
* + 3OO* 2BiBi
high temperature ′ ′′ + 3VO.. + Bi2 O3 ( ↑ ) → 2VBi
(1)
* + OO* 2NaNa
high temperature ′ + VO.. + Na2 O ( ↑ ) → 2VNa
(2)
OO*
high temperature → VO.. + 1/2O2 ( ↑ )
(3)
The XPS spectra and the fitting O 1s spectra of the samples sintered in different atmospheres before irradiation are shown in Fig. 9, and the fitting data are listed in Table 1. It is found that the lattice oxygen peaks representing the Nb–O and A−O bonds are often accompanied by shoulder peaks. Due to the presence of oxygen vacancies, shoulder peaks are usually assigned to absorbed oxygen [44]. Moreover, it can be seen that lattice oxygen peaks and the absorption oxygen peaks do not show significant shift. It is well known that the ratio of the fitting area of lattice oxygen to absorbed oxygen (Vo/O2−) can indicate the VO.. content in ceramic samples. From Table 1, the Vo/O2− value of the sample sintered in N2 (0.43) is obviously lower than that sintered in O2 (0.86) and air (0.57), suggesting that the VO.. content of samples sintered in N2 is the lowest, while the VO.. content of samples sintered in O2 is the 6
Journal of Luminescence 215 (2019) 116626
Y. Zhu, et al.
Fig. 8. Volatilization process of Bi/Na during sintering in different atmospheres.
highest. This is consistent with our test results. In fact, a small amount of VO.. will be filled when sintered in O2, but the value of VO.. caused by the large amount of K and Na volatilization is much larger than the value of the VO.. that are filled. Therefore, the VO.. content in O2 is much higher than the VO.. content in the other 2 atm. According to the relevant literature [45,46], the oxygen vacancies can be used as effective sensitizers for the adjacent rare earth ions to enhance the PL intensity. Therefore, we speculate that oxygen vacancies in NBN matrix can also be used as effective sensitizers for Pr and Er ions. The oxygen vacancies transferred excitation energy to the adjacent rare earth ion sites and thus greatly enhanced PL and UC luminescence intensity of the sample (this process is schematically illustrated in Fig. 10). Based on the XPS results of the VO.. content of samples sintered in N2, we believe that O vacancy change is the main reason for the decreased upconversion and downshifting emission intensities for samples sintered in N2.
Table 1 Fitting parameters of the O 1s XPS spectra of Er doped NBN samples in different atmospheres. Samples
Lattice O (O2−)
Absorbed O (*Vo)
Vo/O2--
Air O2 N2
529.20 eV 529.02 eV 529.27 eV
531.29 eV 531.10 eV 531.83 eV
0.57 0.86 0.43
*Vo means O vacancy.
4. Conclusions Pr3+ and Er3+ co-doped NBN ceramics have been prepared by a conventional solid-state sintering method in air, O2 and N2 atmospheres. Their photoluminescence, upconversion luminescence,
Fig. 9. (a) XPS spectra of NBN sample and O 1s spectra for NBN:0.01Er before irradiation (b) sintered in air, (c) sintered in O2, (d) sintered in N2. 7
Journal of Luminescence 215 (2019) 116626
Y. Zhu, et al.
Fig. 10. The schematic diagram of the energy transfer process mediated by O vacancy. [10] S. Kamimura, H. Yamada, C.N. Xu, Purple photochromism in Sr2SnO4:Eu3+ with layered perovskite-related structure, Appl. Phys. Lett. 102 (2013) 363. [11] Y. Li, Y. Wang, Y. Gong, X. Xu, F. Zhang, Photoionization behavior of Eu2+-doped BaMgSiO4 long-persisting phosphor upon UV irradiation, Acta Mater. 59 (2011) 3174–3183. [12] H.E. Moll, A. Dolbecq, I.M. Mbomekalle, J. Marrot, P. Deniard, R. Dessapt, P. Mialane, Tuning the photochromic properties of molybdenum bisphosphonate polyoxometalates, Inorg. Chem. 51 (2012) 2291–2302. [13] C. Xu, J. Zhang, L. Xu, H. Zhao, Mechanism of photochromic effect in Pb (Zr,Ti) O3 and (Pb,La) (Zr,Ti) O3 ceramics under violet/infrared light illumination, J. Appl. Phys. 117 (2015) 023107. [14] E. Orgiu, P. Samori, 25th anniversary article: organic electronics marries photochromism: generation of multifunctional interfaces, materials, and devices, Adv. Mater. 26 (2014) 1827–1845. [15] M.S. Wang, G. Xu, Z.J. Zhang, G.C. Guo, Inorganic–organic hybrid photochromic materials, Chem. Commun. 46 (2010) 361–376. [16] S.K. Deb, Optical and photoelectric properties and colour centres in thin films of tungsten oxide, Philos. Mag. 27 (1973) 801–822. [17] B.W. Faughnan, R.S. Crandall, M.A. Lampert, Model for the bleaching of WO3 electrochromic films by an electric field, Phys. Rev. Lett. 27 (1975) 275–277. [18] O.F. Schirmer, V. Wittwer, G. Baur, G. Brandt, Dependence of WO3 electrochromic absorption on crystallinity, J. Electrochem. Soc. 124 (1977) 749–753. [19] T. He, J. Yao, Photochromic materials based on tungsten oxide, J. Mater. Chem. 17 (2007) 4547–4557. [20] Y. Wei, Z. Wu, Y. Jia, J. Wu, Y. Shen, H. Luo, Dual-enhancement of ferro-/piezoelectric and photoluminescent performance in Pr3+ doped (K0.5Na0.5) NbO3 leadfree ceramics, Appl. Phys. Lett. 105 (2014) 042902. [21] X. Wang, C.N. Xu, H. Yamada, K. Nishikubo, X.‐G. Zheng, Electro-mechano-optical conversions in Pr3+-doped BaTiO3-CaTiO3, Adv. Mater. 17 (2005) 1254–1258. [22] P. Du, L. Luo, W. Li, Q. Yue, Upconversion emission in Er-doped and Er/Yb-codoped ferroelectric Na0.5Bi0.5TiO3 and its temperature sensing application, J. Appl. Phys. 116 (2014) 014102. [23] Q.W. Zhang, Y. Zhang, H.Q. Sun, W. Geng, X.S. Wang, X.H. Hao, S. L, An, Tunable luminescence contrast of Na0.5Bi4.5Ti4O15: Re (Re=Sm, Pr, Er) photochromics by controlling the excitation energy of luminescent centers, ACS Appl. Mater. Interfaces 8 (2016) 34581–34589. [24] Q.W. Zhang, Y. Zhang, H.Q. Sun, Q. S, X.S. Wang, X.H. Hao, S.L., An, Photoluminescence, photochromism, and reversible luminescence modulation behavior of Sm-doped Na0.5 Bi2.5Nb2O9ferroelectrics, J. Eur. Ceram. Soc. 37 (2017) 955–966. [25] Q.W. Zhang, S.S. Yue, Y. Zhang, H.Q. Sun, X.S. Wang, X.H. Hao, S. L, An, Nondestructive up-conversion readout in Er/Yb co-doped Na0.5Bi2.5Nb2O9-based optical storage materials for optical data storage device applications, J. Mater. Chem. C 5 (2017) 3838–3847. [26] Z.Y. Zhou, Y.C. Li, S.P. Hui, X.L. Dong, Effect of tungsten doping in bismuth-layered Na0.5Bi2.5Nb2O9 high temperature piezoceramics, Appl. Phys. Lett. 104 (2014) 166. [27] C.B. Long, H.Q. Fan, M.M. Li, Q. Li, Crystal structure and enhanced piezoelectric properties of scandium and bismuth-excess modified Aurivillius oxides, Na0.5xBi2.5+xNb2- xScxO9, Eur. J. Inorg. Chem. 32 (2013) 5622–5630. [28] C.B. Long, H.Q. Fan, P.R. Ren, Structure, phase transition behaviors and electrical properties of Nd substituted Aurivillius polycrystallines Na0.5NdxBi2.5-x Nb2O9 (x= 0.1, 0.2, 0.3, and 0.5), Inorg. Chem. 52 (2013) 5045–5054. [29] X. Wu, S.B. Lu, K.W. Kwok, Photoluminescence, electro-optic response and piezoelectric properties in pressureless-sintered Er-doped KNN-based transparent ceramics, J. Alloy. Comp. 695 (2017) 3573–3578. [30] F. Vetrone, J.C. Boyer, J.A. Capobianco, Significance of Yb3+ concentration on the upconversion mechanisms in codoped Y2O3: Er3+, Yb3+ nanocrystals, J. Appl. Phys. 96 (2004) 661–667. [31] S. Chen, M. Wu, L.Q. An, Y.X. Li, S.W. Wang, Strong green and red upconversion emission in Er3+-doped Na1/2Bi1/2TiO3 ceramics, J. Am. Ceram. Soc. 90 (2007) 664–666. [32] H.Q. Sun, Q.W. Zhang, X.S. Wang, M. Gu, Green and red upconversion
photochromism and luminescence modulation properties are systematically investigated. During the course of the study, the samples are found to exhibit excellent multi-color luminescence (red-green), multimode (upconversion/downshifting) luminescence properties. The experimental results show that the samples sintered in air and oxygen are light green and dark green, while the green of the samples sintered in nitrogen disappears. It is worth noting that the sample sintered in N2 at 405 nm has luminescence switching contrast (ΔRt) that is significantly lower than the ΔRt values under air and O2, and the upconversion and downshifting emission intensities are significantly decreased. XPS analysis confirmed that the change of emission intensities and ΔRt value was closely related to defects and traps caused by volatilization of Bi and Na in different atmospheres. Acknowledgment This work was supported by the Natural Science Foundation of China (No. 51562030, 51802164), the Natural Science Foundation of Inner Mongolia (No. 2018JQ06), Program for Young Talents of Science and Technology in Universities of Inner Mongolia Autonomous Region (NJYT-17-A10, NJYT-17-B09), Young Academic Core Program of Inner Mongolia University of Science and Technology (No. 2016YQL01), and the Program for Innovative Research Team in Universities of Inner Mongolia Autonomous Region (NMGIRT-A1605). References [1] R. Pardo, M. Zayat, D. Levy, Photochromic organic–inorganic hybrid materials, Chem. Soc. Rev. 40 (2011) 672–687. [2] H. Tao, J. Yao, Photochromism in composite and hybrid materials based on transition-metal oxides and polyoxometalates, Prog. Mater. Sci. 51 (2006) 810–879. [3] B.A. Reinhardt, L.L. Brott, S.J. Clarson, A.G. Dillard, J.C. Bhatt, R. Kannan, L.X. Yuan, G.S. He, P.N. Prasad, Highly active two-photon Dyes: design, synthesis, and characterization toward application, Chem. Mater. 10 (1998) 1863–1874. [4] L. Ding, L.W. Chung, K. Morokuma, Reaction mechanism of photoinduced decarboxylation of the photoactivatable green fluorescent protein: an ONIOM (QM:MM) study, J. Phys. Chem. C 117 (2013) 1075. [5] J. Boixel, Y.F. Zhu, H.L. Bozec, M.A. Benmensour, A. Boucekkine, K.M. Wong, A. Colombo, D. Roberto, V. Guerchais, D. Jacquemin, Contrasted photochromic and luminescent properties in dinuclear Pt(ii) complexes linked through a central dithienylethene unit, Chem. Commun. 52 (2016) 9833–9836. [6] H.B. Cheng, G.F. Hu, Z.H. Zhang, L. Gao, X.F. Gao, H.C. Wu, Photocontrolled reversible luminescent lanthanide molecular switch based on a diarylethene-europium dyad, Inorg. Chem. 55 (2016) 7962–7968. [7] B.W. Faughnan, Z.J. Kiss, Photoinduced reversible charge-transfer processes in transition-metal-doped single-crystal SrTiO3 and TiO2, Phys. Rev. Lett. 21 (1968) 1331. [8] K. Ajito, L.A. Nagahara, D.A. Tryk, K. Hashimoto, A. Fujishima, Study of the photochromic properties of amorphous MoO3 films using Raman microscopy, J. Phys. Chem. 99 (1995) 16383–16388. [9] C.S. Blackman, I.P. Parkin, Atmospheric pressure chemical vapor deposition of crystalline monoclinic WO3 and WO3-x thin films from reaction of WCl6 with Ocontaining solvents and their photochromic and electrochromic properties, Chem. Mater. 17 (2005) 1583–1590.
8
Journal of Luminescence 215 (2019) 116626
Y. Zhu, et al.
[33]
[34]
[35]
[36]
[37] [38]
[39]
luminescence of Er3+ -doped K0.5Na0.5NbO3 ceramics, Ceram. Int. 40 (2014) 2581–2584. Z. Pan, S.H. Morgan, A. Loper, V. King, B.H. Long, W. E, Collins Infrared to visible upconversion in Er3+-doped-lead-germanate glass: effects of Er3+ ion concentration, J. Appl. Phys. 77 (1995) 4688–4692. C. Xu, J. Zhang, L. Xu, H. Zhao, Mechanism of photochromic effect in Pb(Zr,Ti) O3 and (Pb,La) (Zr,Ti) O3 ceramics under violet/infrared light illumination, J. Appl. Phys. 117 (2015) 023107. H.Q. Sun, J. Liu, X.S. Wang, Q.W. Zhang, X.H. Hao, S.L. An, (K,Na)NbO3 ferroelectrics: a new class of solid-state photochromic materials with reversible luminescence switching behavior, J. Mater. Chem. C 5 (2017) 9080–9087. Y. Zhuang, J. Ueda, S. Tanabe, Photochromism and white long-lasting persistent luminescence in Bi3+-doped ZnGa2O4 ceramics, Opt. Mater. Express 2 (2012) 1378–1383. F.M. Raymo, M. Tomasulo, Fluorescence modulation with photochromic switches, J. Phys. Chem. A 109 (2005) 7343–7352. Y. Zhang, J. Liu, H.Q. Sun, D.F. Peng, R.H. Li, C. Bulin, X.S. Wang, Q.W. Zhang, X.H. Hao, Reversible luminescence modulation of Ho-doped K0.5Na0.5NbO3 piezoelectrics with high luminescence contrast, J. Am. Ceram. Soc. 101 (2017) 2305–2312. Q.W. Zhang, H.Q. Sun, X.S. Wang, X.H. Hao, S.L. An, Reversible luminescence modulation upon photochromic reactions in rare-earth doped ferroelectric oxides by in situ photoluminescence spectroscopy, ACS Appl. Mater. Interfaces 7 (2015)
25289–25297. [40] Q.W. Zhang, X.W. Zheng, H.Q. Sun, W.Q. Li, X.S. Wang, X.H. Hao, S. L, An, dualmode luminescence modulation upon visible-light-driven photochromism with high contrast for inorganic luminescence ferroelectrics, ACS Appl. Mater. Interfaces 8 (2016) 4789–4794. [41] J.S. Hong, Y.H. Huang, Y.J. Wu, M.S. Fu, J. Li, X.Q. Liu, Oxygen-vacancy-induced reversible control of ferroelectric polarization in Ba4Eu2Fe2Nb8O30 ceramics, J. Appl. Phys. 124 (2018) 064105. [42] Z.Y. Cen, X.H. Wang, Y. Huan, Y.C. Zhen, W. Feng, L.T. Li, Defect engineering on phase structure and temperature stability of KNN-based ceramics sintered in different atmospheres, J. Am. Ceram. Soc. 101 (2018) 3032–3043. [43] H.C. Thong, Q. Li, M.H. Zhang, C.L. Zhao, K.X. Huang, J.F. Li, K. Wang, Defect suppression in CaZrO3-modified (K,Na)NbO3-based lead-free piezoceramic by sintering atmosphere control, J. Am. Ceram. Soc. 101 (2018) 3393–3401. [44] T. Saitoh, Electronic structure of La1-xSrxMnO3 studied by photoemission and x-rayabsorption spectroscopy, Phys. Rev. B 51 (1995) 13942–13951. [45] Y.Z. Xie, Z.W. Ma, L.X. Liu, Y.R. Su, H.T. Zhao, Y.X. Liu, Z.X. Zhang, H.G. Duan, J. Li, E.Q. Xie, Oxygen defects-modulated green photoluminescence of Tb-doped ZrO2 nanofibers, Appl. Phys. Lett. 97 (2010) 141916. [46] S. Kim, S.J. Rhee, D.A. Turnbull, E.E. Reuter, X. Li, J.J. Coleman, S. G, Bishop Observation of multiple Er3+ sites in Er-implanted GaN by site-selective photoluminescence excitation spectroscopy, Appl. Phys. Lett. 71 (1997) 231–233.
9