Tunable Luminescence Contrast in Photochromic Ceramics (1-x)Na0

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Functional Inorganic Materials and Devices

Tunable Luminescence Contrast in Photochromic Ceramics (1x)Na0.5Bi0.5TiO3-xNa0.5K0.5NbO3:0.002Er by an Electric Field Poling Kaixuan Li, Laihui Luo, Yuanyuan Zhang, Weiping Li, and Yafei Hou ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b15784 • Publication Date (Web): 08 Nov 2018 Downloaded from http://pubs.acs.org on November 8, 2018

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ACS Applied Materials & Interfaces

Tunable Luminescence Contrast in Photochromic Ceramics (1-x)Na0.5Bi0.5TiO3-xNa0.5K0.5NbO3:0.002Er by an Electric Field Poling Kaixuan Li, Laihui Luo*, Yuanyuan Zhang, Weiping Li, Yafei Hou Department of Microelectronic Science and Engineering, School of Science, Ningbo University, Ningbo 315211, China *E-mail: [email protected]; [email protected] Abstract: A binary solid solution of Er3+ doped (1-x)Na0.5Bi0.5TiO3-xK0.5Na0.5NbO3 (x=0.02, 0.04, 0.06, 0.08, 0.10, 0.12) ferroelectric ceramics has been developed, and a reversible photochromic (PC) reaction and its associated luminescence modulation are realized via alternating the 405-nm light irradiation and thermal stimulation (200 oC). The basic crystal structure, domain structure, ferroelectricity and dielectric behavior of the ceramics were measured. A moderate luminescence contrast ΔRt over 50% is obtained in the fresh samples. Meanwhile, a greatly enhanced luminescence contrast ΔRt is obtained via an electric poling for compositions x=0.02, 0.04, 0.06. For example, ΔRt is promoted from 53.4% to 85.3% for x=0.02. However, the luminescence contrast ΔRt of compositions x=0.08, 0.10, 0.12 is depressed after poling. The mechanisms of enhanced PC reaction and luminescence contrast ΔRt are discussed and proposed. The present study may open a window for enhancing the PC reaction. Keywords: Luminescence modulation, photochromic, ferroelectrics, Ceramics, Poling. 1

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1. INTRODUCTION Photochromic (PC) materials with reversible manipulation have been extensively investigated because of their potential applications for optical anti-fake labels, optical switches, information storage, and so on.1-3 PC host materials doped with luminescence activator rare-earth (RE) elements possess a capability of both PC reaction and emission modulation behaviors in one single material, which make them can be used in information storage by the photoluminescence contrast before and after light irradiation.4-6 In other words, the photoluminescence intensity of PC materials before and after light irradiation is strikingly different, which can be responded to the states ‘0’ and ‘1’ in information storage.6,7 It has been widely reported that luminescence emission modulation can be realized in organic materials diarylethenes, fulgides and spiropyrans based on their unique PC performances.8-10 However, the low fatigue resistance and thermal stability of organic materials are unfavorable for their applications in practical optical devices. Recently, a few investigations have been reported on luminescence modulation in the RE doped inorganic ferroelectrics Na0.5Bi2.5Nb2O9 (NBN) and K0.5Na0.5NbO3 (KNN) based on the PC reaction.7,11-13 Their coloration and discoloration processes can be reversibly transformed via alternating light irradiation and thermal stimulation.14,15 The ferroelectrics have been used in information storage based on the two poling states of ferroelectric domains.16,17 Nowadays, higher and higher storage density is required for the information storage. The storage density can be highly increased by combining the ferroelectric and optical memory in the ferroelectrics.18,19 Considering this, it is highly significant to investigate the luminescence emission modulation via PC reactions in ferroelectrics. In our previous investigation, we found that the Er3+ doped Na0.5Bi0.5TiO3 (NBT) ceramics exhibits an excellent luminescence emission modulation behavior via PC reaction.20 NBT-based ceramics, known as their giant electro-strain and ferroelectric properties, have attracted much attention due to their lead-free composition and much progress has been made during the recent decade.21-24 For NBT-based ceramics, the 2


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composition, electric poling, mechanical condition etc. greatly influence their crystal structure. Accordingly, the dielectric, ferroelectric and piezoelectric properties are changed.18 The NBT-based ceramics experiences a phase transition from nonergodic relaxor to ergodic relaxor state when the temperature increases. Furthermore, nonergodic NBT-based relaxors transform into a ferroelectric state with long-range order via a sufficiently large electric field by overcoming the strong internal random fields. In contrast, the field-induced long ranged ferroelectric state is not stable in the ergodic relaxors when the external field is removed.25,26 For the poled ceramics, there exists a ferroelectric-relaxor transition temperature TF-R during heating.18 It is reported that

K0.5Na0.5NbO3

(KNN)

modified

NBT

ceramics

owns

the

largest

electric-field-induced strain in all the lead-free systems,22,27 which is even larger than the Pb-based Pb(Zr,Ti)O3 ceramics. Usually, the largest strain is obtained around the depolarization temperature Td, namely ferroelectric-relaxor transition. At temperatures above TF-R (~180oC for NBT), these ceramics possess a reversible large electric-field-induced strain due to the thermally induced ergodic state, which is caused by the increased random fields and vanished ferroelectric phase because of the enhanced thermal effects.28 On the other side, the composition and cation disorder can also induce the ergodicity in NBT-based ceramics at room temperature, such as a introduction of K0.5Na0.5NbO3 (KNN),29 KNbO3 (KN),30 SrTiO3 (ST),31 associated with a dramatically decreased TF-R. When the NBT-based ceramics undergo a transition from nonergodicity to ergodicity with the enhanced composition disorder or increased temperature, their crystal structure and polarity are distinctly different, resulting in a great change of physical properties. However, it is to be known that what will happen to the PC and luminescence modulation properties for the NBT-based ceramics when they transit from nonergodic to ergodic state? In the present study, the PC and luminescence modulation properties were investigated as a function of KNN content in the Er3+ doped (1-x)NBT-xKNN ceramics with 0≤x≤0.12, and we found that the electric poling has an evidently different effect on the (1-x)NBT-xKNN ceramics as the ceramics transit from nonergodic to ergodic ferroelectrics. The correlation 3



between the macroscopical properties and local structure is elucidated by measuring the PC performances, ferroelectricity, and piezoresponse force microscopy (PFM). 2. EXPERIMENTAL SECTION. 2.1 Sample Preparation Process The Er3+ doped (1-x)NBT:xKNN (x=0.02, 0.04, 0.06, 0.08, 0.10, 0.12) samples were prepared by a traditional solid-state reaction sintering method. According to the chemical formula (1-x)NBT:xKNN:0.002Er, powders of Na2CO3, K2CO3, Bi2O3, TiO2, Nb2O5, and Er2O3 of raw materials with high purity were weighted and ball-milled in the matrix of ethanol for 12 h. The obtained slurries were completely dried at 80 oC and pre-sintered at 800 oC for 2 h. And then the as prepared powders were ball-milled in alcohol once more. Next the dried powders were completely mixed with poly (vinyl alcohol) solution (5 wt %). The mixed powders were formed into a shape of disk with a thickness around 1 mm by a pressure and sintered at a temperature of 1200oC for 4 h. Silver electrodes were pasted on the two sides of samples for the ferroelectric measurements, dielectric tests and electric poling. The prepared ceramics were poled by an electric field (55 kV/cm) for 20 min at ambient temperature. 2.2 Sample Characterization The crystal structure of (1-x)NBT:xKNN:0.002Er ceramic wafers was measured by an X-ray diffractometer (XRD, D8 Advance, Bruker) using Cu Kα1 radiation. The surface microstructure of the ceramics was obtained by a scanning electron microscopy (SEM, Hitachi SUS-700). A spectrofluorometer (FS5, Edinburgh Instrument, UK) equipped with a 980-nm diode laser was used to record the upconversion (UC) luminescence spectra. And the xenon lamp from the FS5 spectrofluorometer was used as the irradiation source for the PC reaction, the wavelength of irradiation light is set to be 405 nm. During irradiation, A 10 nm spectral bandwidth was set to the irradiation light. The ferroelectric loops were recorded using a ferroelectric analyzer (Premier II, Radiant Technologies, U. S.). The variation of dielectric performances with temperature was tested by Agilent 4294A impedance analyzer and PTS-2000H measuring system (Partulab, Wuhan, China). The PFM study was measured by an atomic force microscope (Cypher-HV, Asylum 4


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Research, U.S.). 3. RESULTS AND DISCUSSION 3.1 XRD pattern and SEM structure Figure 1(a) presents the XRD patterns for all the prepared specimens. No obvious impure phase is observed within detection resolution of our XRD analyzer, indicating that all the (1-x)NBT-xKNN:0.002Er samples have a pure perovskite phase at room temperature, demonstrating that the K+, Na+, Nb5+ and Er3+ ions have been diffused into the lattices of NBT grain and forming a solid solution of (1-x)NBT-xKNN:0.002Er. Recent investigations illustrate that the pure NBT powder could be an average structural distortion of monoclinic (Cc) and rhombohedral (R3c) phases,32,33 which depends on its thermal and mechanical history. In present context, two obvious split peaks at both {110}pc and {111}pc are observed for compositions x=0.02 and 0.04 (Fig. 1(b), and (c)). And the {110}pc profile is doublet, instead of triplet. Meanwhile the Cc NBT features a triplet {110}pc diffraction pattern. Therefore, the (1-x)NBT-xKNN:0.002Er (x=0.02 and 0.04) ceramics are reasonable to be considered to be as rhombohedral. As for x=0.06 and 0.08, the {110}pc and {111}pc profiles become very broad, and one can notice a doublet {200}pc diffraction pattern (Fig. 1(d)). These results suggest that rhombohedral and tetragonal phases coexist at morphtropic phase34 may forms at x=0.06 and 0.08. As x increases to 0.10 and 0.12, no obvious split peaks for all the {110}pc, {111}pc and {111}pc diffraction planes, which is a typical characteristic for the cublike/pseudocupic NBT ceramics. It is important to note that although the dramatic collapse of the rhombohedral lattice distortion with the increasing KNN content, the structure is not truly cubic for x=0.10 and 0.12. Furthermore, the position of the diffraction peaks shifts little, which is ascribed to the close ions’ radii of NBT and KNN. To examine the density of the prepared ceramics, the SEM morphology was measured, as shown in Fig. 2. No obvious pore is perceived for all the ceramics, illustrating that all the ceramics were well sintered. Under the same sintering temperature of 1200 oC, the grain size shows a mild decreasing trend with the increasing KNN content. 3.2 Ferroelectric and Dielectric Properties 5



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The polarization (P-E) and current (I-E) loops of (1-x)NBT-xKNN:0.002Er ceramic are shown in Fig. 3(a)-(f), respectively. For the 0.98NBT-0.02KNN:0.002Er and 0.98NBT-0.04KNN:0.002Er, they show a rectangle-like P-E loops and their polarization is achieved under the maximal electric field of 75 kV/cm (Fig. 3(a) and (b)). For the I-E loops, two sharp current peaks, as marked in Fig. 3(a) and (b), are perceived at the coercive field ±EC, which is ascribed to the domain switching of long ranged ferroelectric order under electric field.35,36 However, as the KNN content further increases to x=0.06, the P-E loops become a little slim and inclined. Specially, four obvious current peaks ±EB and ±EF are observed. The subscripts F and B mean forward and backward. These four current peaks are related to the inter transformation between ferroelectric order and weak polar phases when loading and unloading the electric field.36,37 When loading the electric field, weak polar P4bm phase in the 0.98NBT-0.06KNN:0.002Er transits to the R3c phase with ferroelectric order at ±EF. However, the induced polar order R3c phase from P4bm by the electric field is reversible due to the existence of the ergodic state in the 0.98NBT-0.06KNN:0.002Er ceramics, and it return to its initial state when unloading the field at ±EB. With the further increasing of the KNN content to x=0.08, 0.10, the distance between EB and EF becomes larger. Namely, it requires a larger electric field to induce or maintain a long-ranged ferroelectric order due to the increasing content of ergodic state with the increasing KNN content. Compared with composition x=0.06, +EB shifts to a negative value for compositions x=0.08, 0.10, indicating that the induced long ranged ferroelectric order is not stable and require an external electric field to maintain. Also the remnant polarization is decreased dramatically for compositions x=0.08, 0.10. This result reconfirms that the induced ferroelectric order cannot be reserved without external field. However, for x=0.12, the current curve becomes flat, and the no obvious

hysteresis

is

observed

for

the

P-E

loops,

indicating

that

the

0.88NBT-0.12KNN:0.002Er has been transformed into a complete ergodic state. For the electric-poled NBT-based ceramics, the depolarization temperature Td (TF-R) is an important parameter, at which they lose the macroscopic piezoelectric response due to the thermally destroyed long range order.38,39 Therefore, the dielectric 6


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constant ε33 and loss tanδ as a function of temperature were measured for all the ceramics after poling. For the 0.98NBT-0.02KNN:0.002Er, as the temperature increases to temperature Td (~105 oC, marked in Fig. 4(a)), a dielectric anomaly is observed, and the dielectric constant becomes more frequency dependent. Furthermore, the loss peaks are diffusive and broad, which indicates the depolarization process happens in a wide temperature range instead of a temperature point. Above Td, there still exists a relaxation behavior, which is considered as the thermal evolution of R3c to P4bm phase.40 And the dielectric anomaly at Tm near 340 oC

is regarded to be related to the P4bm polar nanoregions (PNRs). At Tm, no

evidence demonstrates that a phase transition happens. With further increasing x to 0.06, Td decreases to ~45 oC. It is noted that there still exists a frequency-dependent dielectric constant for the poled ceramics x=0.02, 0.04, 0.06. This is caused by that the poled ceramics still have some nanodomains giving a dynamic fluctuation. And for composition x≥0.08 (Fig. 4(d)-(f)), no depolarization peak is observed. Meanwhile, a obvious dielectric anomaly is observed in the temperature range 100~150 oC, which is caused by the more complex compositions in these ceramics. Such results may be associated with the cooperation between the thermal evolution of R3c to P4bm and the disappeared dielectric dispersion, as usually observed in the NBT-based ceramics.41 However, the Tm dielectric anomaly seems to be depressed. The observed Td evolution with KNN content is consistent with the ferroelectric test. 3.3 PC Reaction To check the PC performances of the prepared samples, the photographs of the (1-x)NBT-xKNN:0.002Er ceramic before and after 405-nm light irradiation were recorded, as shown in Fig. 5. Upon 405-nm light irradiation (as marked I) for 4 min, The color of ceramics becomes from initial pale yellow to dark yellow after irradiation (4 min) as a colored samples, and those samples are recovered to their initial stage by a thermal stimulus bleaching (200 oC for 10 min, recorded as Δ). Surprisingly, the corlor of the poled and irradiated ceramics (x=0.02, 0.04) is much deeper than the only irradiated counterparts. Here, the combination of poling and irradiations is recorded as I-P. Such results indicate that the electric poling may be a 7



useful approach to increase the degree of PC reaction. The color change will leads to a changed luminescence intensity. To quantitatively describe the PC reaction, diffuse reflection spectra were measured for (1-x)NBT-xKNN:0.002Er ceramics with different treatments: fresh, irradiation, and irradiation after poling, as shown in Fig. 6(a)-(f). The irradiation was carried out by 405-nm light for 4 min. All the samples own four absorption bands centered at 488, 524, 550, and 655 nm in the diffuse reflectance spectra, which are produced by the 4f-4f transitions of the Er3+ ions.12,42 Furthermore, the reflectivity of samples is little dependent on the KNN content. Comparing the reflectance spectra of fresh samples with those of the irradiated ones in visible light region, we found that the reflectance after irradiation has obvious decrement for all the ceramics. The reduced reflectance results in a change of color. Meanwhile, the absorption of Er3+ becomes relative weak after irradiation, which can be ascribed to that the host has a more strong absorption because of its darker color induced by irradiation, and most of light is absorbed by the NBT host. When we compare the reflectance spectra for the irradiated samples with those of the counterparts undergone poling and irradiation in visible light region, ones find that, those poled and irradiated samples with x=0.02, 0.04 have distinct lower reflectivity than the only irradiated ones. However, for x=0.06, poling has a little effect on the reflectance spectra. However, when x≥0.08, the reflectance spectra of these samples with treatment of irradiation, irradiation after poling are always the same. this result demonstrates that poling has no effect on the reflectance spectra for x≥0.08. 3.4 Properties of Luminescence Modulation Figure 7(a) shows the typical change of the UC luminescence spectra for composition x=0.02 (not poled) after 405-nm irradiation for different time. Obviously, they have two green emission peaks located at 530 and 550 nm, assigning to the transitions of 2H11/2→4I15/2 and 4S3/2→4I15/2 from Er3+ ions, respectively. The results show that the emission intensity significantly decreases after irradiation for 10 seconds, and with the further increasing irradiation time to 240 s (4 min), the luminescence intensity further decreases (see the inset in Fig. 7(b)) but with a much 8


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lower decreasing rate. To quantitatively describe the decrement of luminescence intensity, luminescence modification contrast is introduced. The luminescence modification contrast (ΔRt) can be calculated by ΔRt=(R0–Rt)/R0×100(%), where R0 is the initial luninescence intensity, and Rt is that after different irradiation time. As shown in Fig. 7(b), ΔRt values for all the prepared compositions increase with increasing irradiation times. The ΔRt for all the ceramics is in a range of 47~49% after 4 min irradiation, indicating that the KNN content has little influence on the luminescence modification performances. Erasable optical storage requires a reversible luminescence modulation. Considering this factor, the fatigue properties of the ceramics on the luminescence modulation are studied. Figure 8 shows 10 cycles of the UC luminescence modulation for all the ceramics by alternating light irradiation for 4 minutes and the thermal stimulus at 200 °C for 10 minutes. No obvious decrement and a low fluctuation within 10 cycles are obtained for all the ceramics, suggesting an excellent reversibility and repeatability of UC modification. 3.4 Enhanced UC Luminescence Modulation In view of that the physical performances of (1-x)NBT-xKNN:0.002Er ceramics depend on the undergone electrical history as mentioned above, the poling effect on the luminescence modulation behavior has been studied. Figures 9(a)-(f) show the UC spectra for the poled and unpoled samples with a treatment of 4 min irradiation. For the unpoled sample x=0.02, the UC intensity after a light irradiation of 4 min decreases to 46.6% of that of the fresh sample, and ΔRt is calculated to be 53.4%. Interestingly, For the poled and irradiated sample, its luminescence intensity is only 14.7% of that of the fresh counterpart. Accordingly, its ΔRt value is enhanced to 85.3%. The ΔRt of the poled ceramic is 160% of that of the unpoled one. Similarly, ΔRt of the poled ceramics (x=0.04, and 0.06) is also greatly enhanced via an electric field poling. Their ΔRt are promoted from initial 53.1% to 79.9%, and from 51.4% to 73.2% for x=0.04 and x=0.06, respectively (Fig. 9(b), (c)). However, when x≥0.08 (Fig. 9(d)-(f)), the poled ceramics have no positive effect on the PC modulation. Conversely, the poled ceramics own lower ΔRt than the unpoled ones. We note that 9



the ferroelectricity and depolarization temperature have same trend with the enhancement of ΔRt by poling. Namely, for x=0.02, 0.04, and 0.06, Td is higher than room temperature, others lower than the measuring temperature. The long ranged ferroelectric order can be reserved in these three compositions. Meanwhile, the PC reaction and the luminescence modulation behavior can be enhanced by the electric poling. Therefore, we can anticipate that the enhancement of ΔRt is tightly correlated with polar regions in the ceramics. 3.5 Mechanism of UC luminescence modification The mechanisms of UC and luminescence modulation are showed in Fig. 10. The simplified energy levels are shown on left side of Fig. 10. Upon 980-nm light excitation, there are two emission peaks from Er3+ luminescent centers. The electrons located at ground level 4I15/2 are excited to the 4I11/2, and next populated to 4F7/2 level by excited state absorption (ESA). Subsequently, They are nonradiatively relaxed to 2H

11/2

and 4S3/2 levels. At last, the two 530 and 550 nm emissions are generated by the

electron transitions 2H11/2 and 4S3/2 → 4I15/2, respectively.42,43 K, Na, and Bi tend to '' volatilize when high temperature sintering. As a result, defects VNa , VBi'' , Vk'' , VO

are formed in the ceramics.11,13,20,44 Consequently, defect energy levels are produced between the conduction band and valence band. Under 405-nm light irradiation, electrons are excited to the defect energy levels and trapped by the VO . And the '' , and formed holes are trapped by vacancies of A-sites (mainly containing VBi'' , VNa

Vk'' ). As a result, color centers form.45,46 This process responds to a color one. While thermally stimulated, electrons are detrapped. Next, a recombination between the electrons and holes happens, which leads to a disappearing of the color centers. Such process is a discoloration one. Since the green luminescence emission of Er3+ overlaps the absorption induced by the PC reaction, the luminescence centers Er3+ transfer its energy to the color centers. This process weakens the UC emissions of Er3+ ions.11-13 Therefore, the UC luminescence emission of Er3+ can be effectively controlled by the coloration and discoloration process. 10


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3.6 Mechanism of enhanced PC and ΔRt by poling To observe the evolution of polar structure of the ceramics with the KNN content, the polar structure and its switching behaviors of compositions x=0.02, 0.06, 0.12 are tested by PFM. Figure 11 shows the topography, piezoelectric response, phase for three typical compositions x=0.02, 0.06, 0.12, respectively. No obvious coupling is observed between the topography and amplitude/phase for these images. A clear contrast both for piezoelectric amplitude and phase (Fig. 11(b), (c)) is obtained for x=0.02, illustrating the existence of nanometer-sized domain in the ceramics. However, no obvious domain boundary is tested. For compositions x=0.06, 0.12, neither the amplitude nor the phase has clear contrast (see Fig. 11(e),(f),(h),(i)). The absence of the contrast is typical for the NBT-based ceramics with week ferroelectric properties and was previously reported in similar compositons.47 Usually, the typical PNRs of the NBT-based ceramics can hardly be identified through the common PFM tips.48 The PFM results demonstrate that the size of polar regions becomes smaller with the increment of KNN content in the prepared ceramics. To observe the switching behavior of the polar regions, we applied a 20 V dc voltage when line scanning the well-polished surface of the ceramics using a contact mode. After poling by the tip, the PFM images was scanned immediately considering the tip-induced domain switching for the ferroelectrics is unstable with time. As shown in Fig. 12 (a), (c), and (e), obvious contrast is induced. In Fig.12(a), we find that the poling area is deformed, not a regular rectangular. Figure 12(c) and (e) shows a regular hollow rectangulara, which is exactly the same with the designed shape. This result demonstrates that the polar regions have stronger interaction for compositions x=0.02 than x=0.06, 0.12, suggesting a higher degree of nonergodicity at x=0.02. Meanwhile, Fig. 12(b) also shows a stable phase difference of 180o between the poled and unpoled areas along line AB. While the phase of compositions x=0.06, 0.12 have large fluctuation along line AB (Fig. 12(d), (f)). And the phase difference between the poled and nonpoled regions becomes smaller and smaller with the increment of KNN contents, indicating that the relaxation becomes more strong, which is consistent with the macroscopic dielectric and ferroelectric tests. 11



For compositions x=0.02, 0.04, and 0.06, the PC performance and UC luminescence modulation can be enhanced by a simple electric poling. Although, new phases may be induced via poling in NBT-based ceramics, the free energy between the induced phase and parent phase is nearly equal due to their close lattice parameters.49 Thus we can expect that the phase structure has little effect on the PC performance and UC luminescence modulation. Stable long ranged ferroelectric order could be induced for the nonergodic NBT-based samples by a sufficiently large electric field. From the dielectric and ferroelectric measurements, we know that the compositions x=0.02, 0.04, and 0.06 are nonergodic, and stable long ranged ferroelectric order is preserved after applying the electric poling. The dielectric vs. temperature measurements also support this assumption. Before poling, the ceramics x=0.02, 0.04, and 0.06 illustrate a state of PNRs. Under an irradiation of light irradiation, electrons and holes are generated. Meanwhile, most of the produced electrons and holes recombine immediately due to their ineffective separation, as presented in Fig. 13(a). The others are trapped by the defects, making color centers, which is a color process. Therefore, the degree of PC reaction is relatively low for the unpoled samples due to the limited trapped electrons and holes.　However, the poled ceramics have a completely different behavior of PC reaction (Fig. 13(b)). Upon an application of poling with sufficiently strong electric field, the PNRs in the NBT-based ceramics transit to ordered ferroelectric domains by overcoming the random electric field generated by the composition and charge disorder. Therefore, The internal electric field in the ceramics are greatly enhanced due to the forming of the ferroelectric domains. Choi et al. reported that the internal electric field formed by the spontaneous polarization in BiFeO3 could effectively separated the electrons and holes exited by photons.50 Similarly, the light-induced electrons and holes in the present case can be more effectively separated after poling due to the largely increased internal field. Naturally, the luminescence modulation ΔRt associated with the PC reaction is greatly increased, as obtained above. However, for the ergodic compositions, long ranged ferroelectric order cannot be preserved by the poling electric field due to the weak interaction between the PNRs, which is caused by the 12


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enhanced random field due to the increasing composition and valance disorder in Aand B-sites with the increment of KNN content. Furthermore, electrons may be injected in the ceramics during poling, and they are trapped in the defect levels.42 Therefore, some effective defect levels are preoccupied, resulting in a lower luminescence contrast ΔRt after poling. 4. CONCLUSIONS In this study, new PC ferroelectric ceramics (1-x)NBT-xKNN:0.002Er have been developed. With the increasing KNN content, the ferroelectricity is dramatically weakened and the depolarization temperature is shifted to a temperature lower than ambient temperature when x over 0.08. In other words, with the increasing KNN content, the degree of ergodicity is enhanced. For compositions x=0.02, 0.04, and 0.06 with strong nonergodicity, the PC reaction and luminescence contrast can be greatly enhanced via an electric field poling because of the forming of long ranged order ferroelectric state in them. Meanwhile, the compositions x=0.08, 0.10, and 0.12 have opposite effect after electric poling. Such opposite poling effect on the PC reaction and luminescence contrast is strongly related to the ergodicity of the ceramics.

ORCID Laihui Luo: 0000-0002-2370-8277

ACKNOWLEDGMENTS This work was funded by the National Natural Science Foundation of China (61378068), Preferential Scientific Projects of Leading and Top-notch Talents Training Projects of Ningbo (NBLJ201801004), Natural Science Foundation of Ningbo (2018A610076), and the K. C. Wong Magna Fund in Ningbo University.

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REFERENCE (1) Yao, J. N.; Hashimoto, K.; Fujishima, A. Photochromism Induced in an Electrolytically Pretreated MoO3 Thin Film by Visible Light. Nature 1992, 355, 624-626. (2) Hadjoudis, E.; Mavridis, I. M. Photochromism and Thermochromism of Schiff Bases in the Solid State: Structural Aspects. Chem. Soc. Rev. 2004, 33, 579-588. (3) Yamase, T. Photo-and Electrochromism of Polyoxometalates and Related Materials. Chem. Rev. 1998, 98307-326. (4) Ebisawa, F.; Hoshino, M.; Sukegawa, K. Self-holding Photochromic Polymer Mach–Zehnder Optical Switch. Appl. Phys. Lett. 1994, 65, 2919-2921. (5) Helmy, S.; Leibfarth, F. A.; Oh, S.; Poema, J. E.; Hawker, C. J.; de Alaniz, J. R. Photoswitching Using Visible Light: A New Class of Organic Photochromic Molecules. J. Am. Chem. Soc. 2014, 136, 8169-8172. (6) Berberich, M.; Krause, A. M.; Orlandi, M.; Scandola, F.; Würthner, F. Toward Fluorescent Memories with Nondestructive Readout: Photoswitching of Fluorescence by Intramolecular Electron Transfer in a Diaryl Ethene-Perylene Bisimide Photochromic System. Angew. Chem. 2008, 47, 6616-6619. (7) Zhang, Q.; Liu, J.; Sun, H.; Wang, X.; Hao, X.; An, S. Luminescence Photoswitching of Ho-doped Na0.5Bi2.5Nb2O9 Ferroelectrics: Luminescence Readout Process. J. Mater. Chem. C 2017, 5, 807–816. (8) Irie, M. Diarylethenes for Memories and Switches. Chem. Rev. 2000，100， 1685-1716. (9) Yokoyam, Y. Fulgides for Memories and Switches. Chem. Rev. 2000,100, 1717-1740. (10) Berkovic, G.; Krongauz, V.; Weiss, V. Spiropyrans and Spirooxazines for Memories and Switches. Chem. Rev. 2000, 100, 1741-1754. (11) Zhang, Q.; Zhao, Y.; Sun, H.; Sun, Q.; Wang, X.; Hao, X.; An, S. Photoluminescence, Photochromism and Reversible Luminescence Modulation Behavior of Sm-doped Na0.5Bi2.5Nb2O9 Ferroelectrics. J. Eur. Ceram. Soc. 2017, 37, 955-966. (12) Zhang, Q.; Zheng, X.; Sun, H.; Li, W.; Wang, X.; Hao, X.; An, S. Dual-mode Luminescence Modulation upon Visible-light-driven Photochromism with High Contrast for Inorganic Luminescence Ferroelectrics. ACS Appl. Mater. Interfaces. 2016, 8, 4789-4794. (13) Zhang, Q.; Yue, S.; Sun, H.; Wang, X.; Hao, X.; An, S. 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 2017, 5, 3838-3847. (14) Cohen, A. J.; Smith, H. L. Variable Transmission Silicate Glasses Sensitive to Sunlight. Science 1962,137, 981-981. (15) Blackman, C. S.; Parkin, I. P. Atmospheric Pressure Chemical Vapor Deposition of Crystalline Monoclinic WO3 and WO3-x Thin Films from Reaction of WCl6 with O-containing Solvents and their Photochromic and Electrochromic Properties. Chem. 14


Page 14 of 30

Page 15 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Mater. 2005, 17, 1583-1590. (16) Yao, Q.; Wang, F.; Xu, F.; Leung, C.; Wang, T.; Tang, Y.; Ye, X.; Xie, Y.; Sun, D.; Shi, W. Electric Field-Induced Giant Strain and Photoluminescence-Enhancement Effect in Rare-Earth Modified Lead-Free Piezoelectric Ceramics. ACS Appl. Mater. Interfaces 2015, 7, 5066-5075. (17) Wang, F.; Liu, D.; Chen, Z.; Duan, Z.; Zhang, Y.; Sun, D.; Zhao, X.; Shi, W.; Zheng, R.; Luo, H. In situ Reversible Tuning of Photoluminescence of an Epitaxial Thin Film via Piezoelectric Strain Induced by a Pb(Mg1/3Nb2/3)O3–PbTiO3 Single Crystal. J. Mater. Chem. C 2017, 5, 9115-9120. (18) Sun, H.; Wu, X.; Peng, D. F.; Kwok, K. W. Room-temperature Large and Reversible Modulation of Photoluminescence by in situ Electric Field in Ergodic Relaxor Ferroelectrics. ACS Appl. Mater. Interfaces. 2017, 9, 34042-34049. (19) Sun, H.; Wu, X.; Chung, T. H.; Kwok, K. W. In-situ Electric Field-induced Modulation of Photoluminescence in Pr-doped Ba0.85Ca0.15Ti0.90Zr0.10O3 Lead-free Ceramics. Sci. Rep. 2016, 6, 28677. (20) Li, K.; Luo, L.; Zhang, Y.; Li, W.; Hou, Y. The Up-conversion Luminescence Modulation and its Enhancement of Er3+ Doped Na0.5Bi0.5TiO3 Based on Photochromic Reaction. J. Am. Ceram. Soc. DOI: 10. 111/jace. 15879. (21) Rödel, J.; Jo, W.; Seifert, K. T. P.; Anton, E.; Granzow, T.; Damjanovic, D. Perspective on the Development of Lead-free Piezoceramics. J. Am. Ceram. Soc. 2010, 92, 1153-1177. (22) Zhang, S. T.; Kounga, A. B.; Jo, W.; Jamin, C.; Seifert, K.; Granzow, T.; Rödel, J.; damjanovic, D. High-Strain Lead-free Antiferroelectric Electrostrictors. Adv. Mater. 2009, 21, 4716-4720. (23) Daniels, J. E.; Jo, W.; Rödel, J.; Jones, J. L. Electric-field-induced Phase Transformation at a Lead-free Morphotropic Phase Boundary: Case Study in a 93%(Bi0.5Na0.5)TiO3–7% BaTiO3 Piezoelectric Ceramic. Appl. Phys. Lett. 2009, 95, 032904-032904-3. (24) Krauss, W.; Schütz, D.; Mautner, F. A.; Feteira, A.; Reichmann, K. Piezoelectric Properties and Phase Transition Temperatures of the Solid Solution of (1−x)(Bi0.5Na0.5)TiO3–xSrTiO3. J. Eur. Ceram. Soc. 2010, 30, 1827-1832. (25) Dittmer, R.; Gobeljic, D.; Jo, W.; Shvartsman, V. V.; Lupascu, D.C.; Jones, J. L.; Rödel, J. Ergodicity Reflected in Macroscopic and Microscopic Field-Dependent Behavior of BNT-Based Relaxors. J. Appl. Phys. 2014, 115, 084111-24. (26) Gobeljic, D.; Dittmer, R.; Rödel, J.; Shvartsman, V. V.; Lupascu, D. C. Macroscopic and Nanoscopic Polarization Relaxation Kinetics in Lead-Free Relaxors Bi1/2Na1/2TiO3-Bi1/2K1/2TiO3-BiZn1/2Ti1/2O3. J. Am. Ceram. Soc. 2014, 97, 3904−3912. (27) Zhang, S. T.; Kounga, A. B.; Aulbach, E.; Rödel, J. Giant Strain in Lead-free Piezoceramics Bi0.5Na0.5TiO3-BaTiO3-K0.5Na0.5NbO3 System. Appl. Phys. Lett. 2007, 91, 1120906-112906-3. (28) Jo, W.; Granzow, T.; Aulbach, E.; Rödel, J.; Damjanovic, D. Origin of the Large Strain Response in (K0.5Na0.5)NbO3-Modified (Bi0.5Na0.5)TiO3-BaTiO3 Lead-Free Piezoceramics. J. Appl. Phys. 2009,105, 094102-094102-5. 15



(29) Swain, S.; Kumar, P.; Agrawal, D. K.; Sonia. Dielectric and Ferroelectric Study of KNN Modified NBT Ceramics Synthesized by Microwave Processing Technique. Ceram. Int. 2013, 39, 3205-3210. (30) Luo, L.; Wang, B.; Jiang, X.; Li, W. Energy Storage Properties of (1-x)(Bi0.5 Na0.5 )TiO3-xKNbO3 Lead-Free Ceramics. J. Mater. Sci. 2014, 213,1659-1665. (31) Cao, W.; Li, W.; Dai, X.; Zhang, T.; Sheng, J.; Hou, Y.; Fei, W. Large Electrocaloric Response and High Energy-storage Properties over a Broad Temperature Range in Lead-free NBT-ST Ceramics. J. Eur. Ceram. Soc. 2016, 36, 593-600. (32) Levin, I.; Reaney, I. M.; Nano-and Mesoscale Structure of Na½Bi½TiO3: A TEM Perspective. Adv. Funct. Mater. 2012, 22, 3445–3452. (33) Khatua, D. K.; Mehrotra, T.; Mishra, A.; Majumdar, B.; Senyshyn, A.; Ranjan, R. Anomalous Influence of Grain Size on the Global Structure, Ferroelectric and Piezoelectric Response of Na0.5Bi0.5TiO3. Acta Mater. 2017, 134, 177-187. (34) Kounga, A. B.; Zhang, S.-T.; Jo W.; Granzow, T.; Rödel, J.; Morphotropic Phase Boundary in Lead-free Piezoceramics, Appl. Phys. Lett. 2008, 92, 222902. (35) Viola, G.; McKinnon, R.; Koval, V.; Adomkevicius, A.; Dunn, S.; Yan, H. Lithium-induced Phase Transitions in Lead-free Bi0.5Na0.5TiO3 Based Ceramics. J. Phys. Chem. C 2014, 118, 8564–8570. (36) Viola, G.; Ning, H.; Reece, M. J.; Wilson, R.; Correia, T. M.; Weaver, P.; Cain, M.G.; Yan, H. Reversibility in Electric Field-induced Transitions and Energy Storage Properties of Bismuth-based Perovskite Ceramics. J. Phys. D: Appl. Phys. 2012, 45, 355302. (37) Liu, X.; Tan, X.; Giant Strains in Non-Textured (Bi1/2Na1/2)TiO3-based Lead-free Ceramics. Adv. Mater. 2016, 28, 574–578. (38) Eerd, B. W.; Damjanovic, D.; Klein, N.; Setter, N.; Trodahl, J. Structural Complexity of (Na0.5Bi0.5) TiO3-BaTiO3 as Revealed by Raman Spectroscopy. Phys. rev. B 2010, 82, 104112. (39) Dittmer, R.; Webbera, K. G.; Aulbach, E.; Jo, W.; Tan, X. L.; Rödel, J. Electric-field-induced Polarization and Strain in 0.94(Bi1/2Na1/2)TiO–0.06BaTiO3 under Uniaxial Stress. Acta Mater. 2013, 61, 1350-1358. (40) Jo, W.; Schaab, S.; Sapper, E.; Schmitt, L.;A.; Kleebe, H. J.; Bell, A. J.; Rödel, J. On the Phase Identity and its Thermal Evolution of Lead Free (Bi1/2Na1/2)TiO3-6mol% BaTiO3. J. Appl.Phys. 2011, 110, 074106. (41) Qiao, X.-s.; Chen, X.-ming, Lian, H.-l., Zhou, J.-p.; Liu, P.; Dielectric, Ferroelectric, Piezoelectric Properties and Impedance analysis of Nonstoichiometric (Bi0.5Na0.5)0.94+xBa0.06TiO3 Ceramics, J. Eur. Ceram. Soc. 2016, 36, 3995–4001 (42) Luo, L.; Du, P.; Li, W.; Tao, W.; Chen, H. Effects of Er Doping Site and Concentration on Piezoelectric, Ferroelectric, and Optical Properties of Ferroelectric Na0.5Bi0.5TiO3. J. Appl. Phys. 2013, 114, 124104-6. (43) Wei, T.; Li, C.; Zhou, Q.; Zou, Y.; Zhang, L. Upconversion Luminescence and Ferroelectric Properties of Er3+ Doped Bi4Ti3O12–SrBi4Ti4O15. Mater Lett. 2014, 118, 92-95. (44) Zhang, Y.; Luo, L.; Li, K.; Li, W.; Hou, Y. Large and Reversible in-situ 16


Page 16 of 30

Page 17 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Up-conversion Photoluminescence Modulation Based on Photochromism via Electric-field and Thermal Stimulus in Ferroelectrics. J. Eur.Ceram. Soc. 2018, 38, 3154-3161. (45) Akiyama M. Blue-green Light Photochromism in Europium Doped BaMgSiO4. Appl. Phys. Lett. 2010;97:181905. (46) Jin, Y.; Lv, Y.; Wang, C.; Ju, G.; Wu, H.; Hu, Y. Design and Control of the Coloration Degree for Photochromic Sr3GdNa(PO4)3F:Eu2+ via Traps Modulation by Ln3+, (Ln=Y, La-Sm, Tb-Lu) Co-doping. Sensor Actuat. B-Chem. 2017, 245, 256-262. (47) Dittmer, R.; Jo, W.; Rödel, J.; Kalinin, S.; Balke, N. Nanoscale Insight Into Lead-Free BNT-BT-xKNN. Adv. Funct. Mater. 2012, 22, 4208-4215. (48) Zeng, J.; Zhao, K.; Zeng, H.; Zheng, L.; Li, G.; Yin, Q. Domain Structure of [(Na0.7K0.2Li0.1)0.5Bi0.5]TiO3 Ceramics Studied by Piezoresponse Force Microscopy. Mater. Lett. 2009, 63, 1468-1470. (49) Li, F.; Lin, D.; Chen, Z.; Cheng, Z.; Wang, J.; Li, C.; Xu, Z.; Huang, Q.; Liao, X.; Chen L. Q.; Shrout T. R.; Zhang S.; Ultrahigh Piezoelectricity in Ferroelectric Ceramics by Design, Nature Mater. 2018,17, 349–354. (50) Choi, T.; Lee, S.; Choi, Y. J.; Kiryukhin, V.; Cheong, S. W. Switchable Ferroelectric Diode and Photovoltaic Effect in BiFeO3. Science 2009, 324, 63-66.

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Captions: Figure 1 (a) XRD patterns of (1-x)NBT-xKNN:0.002Er ceramic; (b), (c), and (d) are the zoomed {110}pc, {111}pc and {200}pc diffraction patterns, respectively. Figure 2 SEM images of the (1-x)NBT-xKNN:0.002Er ceramics: (a) x=0.02, (b) x=0.04, (c) x=0.06, (d) x=0.08, (e) x=0.10, (f) x=0.12. Figure 3 P-E and I-E curves for the (1-x)NBT-xKNN:0.002Er ceramics at room temperature (a) x=0.02, (b) x=0.04, (c) x=0.06, (d) x=0.08, (e) x=0.10, (f) x=0.12. Figure 4 Temperature-dependent dielectric behavior and dielectric loss of the poled (1-x)NBT-xKNN:0.002Er (a) x=0.02, (b) x=0.04, (c) x=0.06 , (d) x=0.8, (e) x=0.10, (f) x=0.12. The inset in (a), (b), (c) are the zoomed dielectric loss near Td. Figure 5 Photographs of (1-x)NBT-xKNN:0.002Er ceramics with alternating heat stimulus (Δ) and irradiation (I)/a combination of poling and irradiation (abbreviated as P-I) Figure 6 Reflection spectra for the (1-x)NBT-xKNN:0.002Er ceramics after different treatment: fresh, irradiation and irradiation after poling. (a) x=0.02, (b) x=0.04, (c) x=0.06, (d) x=0.08, (e) x=0.10, (f) x=0.12. Figure 7 (a) UC luminescence spectra of the 0.98NBT-0.02KNN:0.002Er ceramics modulated by 405-nm irradiation with different time, and the inset in (a) is the intensity of 4S3/2→4I15/2 emission peaks, (b) ΔRt of the ceramics after irradiated for different time. Figure 8 UC luminescence emission modulation contrast ΔRt through alternating light irradiation and heat stimulus for 10 cycles: (a) x=0.02, (b) x=0.04, (c) x=0.06, (d) x=0.08, (e) x=0.10, (f) x=0.12. Figure 9 The UC spectra of the poled and fresh ceramics before and after 4 min light irradiation: (a) x=0.02, (b) x=0.04, (c) x=0.06, (d) x=0.08, (e) x=0.10, (f) x=0.12. Figure 10 The mechanism of UC emission and its modification for Er3+. Figure 11 shows the topography, piezoelectric response, and phase image of compositions (a-c) x=0.02, (d-f) 0.06, (g-i) 0.12, respectively. The scanning area is 5×5 μm2. 18


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Figure 12 Phase image of compositions (a) x=0.02, (c) 0.06, (e) 0.12; (b), (d), and (f) are the phase distribution along the blue line AB in (a), (c), and (e) respectively. Figure 13 The proposed mechanism for the enhanced PC reaction by poling. (a) the poled, (b) the unpoled.

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Figure 1 (a) XRD patterns of (1-x)NBT-xKNN:0.002Er ceramic; (b), (c), and (d) are the zoomed {110}pc, {111}pc and {200}pc diffraction patterns, respectively.

Figure 2 SEM images of the (1-x)NBT-xKNN:0.002Er ceramics: (a) x=0.02, (b) x=0.04, (c) x=0.06, (d) x=0.08, (e) x=0.10, (f) x=0.12.


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Figure 3 P-E and I-E curves for the (1-x)NBT-xKNN:0.002Er ceramics at room temperature (a) x=0.02, (b) x=0.04, (c) x=0.06, (d) x=0.08, (e) x=0.10, (f) x=0.12.



Figure 4 Temperature-dependent dielectric behavior and dielectric loss of the poled (1-x)NBT-xKNN:0.002Er (a) x=0.02, (b) x=0.04, (c) x=0.06 , (d) x=0.8, (e) x=0.10, (f) x=0.12. The inset in (a), (b), (c) are the zoomed dielectric loss near Td.


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Figure 5 Photographs of (1-x)NBT-xKNN:0.002Er ceramics with alternating heat stimulus (Δ) and irradiation (I)/a combination of poling and irradiation (abbreviated as P-I)



Figure 6 Reflection spectra for the (1-x)NBT-xKNN:0.002Er ceramics after different treatment: fresh, irradiation and irradiation after poling. (a) x=0.02, (b) x=0.04, (c) x=0.06, (d) x=0.08, (e) x=0.10, (f) x=0.12.


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Figure 7 (a) UC luminescence spectra of the 0.98NBT-0.02KNN:0.002Er ceramics modulated by 405-nm irradiation with different time, and the inset in (a) is the intensity of 4S3/2→4I15/2 emission peaks, (b) ΔRt of the ceramics after irradiated for different time.



Figure 8 UC luminescence emission modulation contrast ΔRt through alternating light irradiation and heat stimulus for 10 cycles: (a) x=0.02, (b) x=0.04, (c) x=0.06, (d) x=0.08, (e) x=0.10, (f) x=0.12.


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Figure 9 The UC spectra of the poled and fresh ceramics before and after 4 min light irradiation: (a) x=0.02, (b) x=0.04, (c) x=0.06, (d) x=0.08, (e) x=0.10, (f) x=0.12.



Figure 10 The mechanism of UC emission and its modification for Er3+.

Figure 11 shows the topography, piezoelectric response, and phase image of compositions (a-c) x=0.02, (d-f) 0.06, (g-i) 0.12, respectively. The scanning area is 5×5 μm2.


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Figure 12 Phase image of compositions (a) x=0.02, (c) 0.06, (e) 0.12; (b), (d), and (f) are the phase distribution along the blue line AB in (a), (c), and (e) respectively.



Figure 13 The proposed mechanism for the enhanced PC reaction by poling. (a) the poled, (b) the unpoled.


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Tunable Luminescence Contrast in Photochromic Ceramics (1-x)Na0

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