Multimodal dynamic luminescence of self-activated Na₂CaGe₂O₆ phosphor via defect manipulation†

Nannan Zhu ^a, Ting Wang *^b, Longchao Guo ^a, Xuanyu Zhu ^b, Weifang Bu ^a, Yang Yue ^a and Xue Yu *^ac
aSchool of Mechanical Engineering, Chengdu University, Chengdu 610106, China. E-mail: yuyu6593@126.com
^bCollege of Materials and Chemistry & Chemical Engineering, Chengdu University of Technology, Chengdu 610059, China. E-mail: wangtkm@foxmail.com
^cShandong Laboratory of Advanced Materials and Green Manufacturing at Yantai,

First published on 3rd August 2024

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1. Introduction

The presence of counterfeit and inferior products not only poses a threat to businesses and economies but also undermines consumer benefit and safety.^1–3 Currently, optical functional materials offer a promising remedy in combating counterfeit owing to their merits such as affordability, customizable colors, and ease of identification capabilities.^4–6 In fact, optical encryption materials are characterized by their vivid and colorful emissions, high throughput, and straightforward design, making them ideal candidates for developing advanced encryption techniques. Recently, Yang et al. realized photoluminescence (PL) and mechanoluminescence (ML) by incorporating Bi³⁺ ions into the SrZnSO matrix and achieved a three-mode anti-counterfeiting through distinct optical response under external stimuli.⁷ Li et al. discovered that Bi³⁺/Er³⁺ co-doped Gd₃GaO₆ phosphor exhibits distinct luminous colors under 302, 365, 980 and 1530 nm excitation, endowing a four-mode anti-counterfeiting approach.⁸ Li et al. found that the up-conversion luminescence (UCL) color of Y₂Mo₄O₁₅:Yb³⁺, Ho³⁺ could be regulated when the excitation power density and the pulse width of the excitation light is changed, wherein, it can be employed for multimodal anti-counterfeiting and information encryption applications.^9–12 Although many successes have been achieved, static emission patterns still pose a risk of counterfeiting, necessitating upgrades to ensure information security.

Phosphors with time-dependent luminescent performance are developed for dynamic anti-counterfeiting, including long persistent (LPL),^13–18 photo-stimulated and mechanical luminescence (PSL),^1,19–21 which are related to the filling and release rate of carriers from the traps under the stimulations of thermal disturbance, 980 nm laser and mechanical stimulation, respectively. Sun et al. reported a multi-stimulus-responsive Na₂CaGe₂O₆:Pb²⁺/Er³⁺ phosphor that produces the corresponding PL and UCL under different excitations, and the PSL induces dynamic appearance changes of the printed images.²² Zhang et al. acquired color tunable LPL in Ca₃Al₂Ge₃O₁₂:Mn²⁺, Cr³⁺ by modulating the doping concentrations, pumped excitation energy and operated temperatures.²³ Gao et al. synthesized Zn_1+xGa_2−2xGe_xO₄:Mn (0 ≤ x ≤ 1) solid solution phosphor, which presents green LPL under mechanical stimulation.²⁴ The dynamic luminescence behaviors generally rely on the presence of suitable trap centers.²⁵ Trap centers refer to the energy levels within the bandgap of the corresponding phosphor where charge carriers can be trapped or stored.^26–28 These trap centers enable the storage of the excitation energy, allowing for the release of carriers over an extended period of time under thermal disturbance or 980 nm laser stimulus.^19,29,30 Therefore, effectively manipulating trap centers is crucial for phosphors to regulate their luminescent output.

In fact, self-activated luminescent properties based on its intrinsic defects for germanate phosphors have been investigated for their fascinating optical properties^31–35 such as Na₂ZnGeO₄ and Ca₂Ge₇O₁₆. It has been discovered that the structural manipulation contributes to the optical behavior regulation. Hence, it seems feasible to manipulate the defect centers of the self-activated host, enabling the desired dynamic luminescent behavior. In this work, Na₂CaGe₂O₆ phosphor was explored with their self-activated emissions related to the oxygen vacancy () and inverse site defect (). Moreover, the state of defects could be manipulated with the introduction of Bi³⁺, thereby endowing the matrix with dynamic luminescence performances, including PL, LPL and PSL. Furthermore, it is observed that the increase in irradiation time contributes to the PL color regulation of the corresponding sample, while the recovery of the PL color change could be realized via thermal disturbance. Additionally, the LPL and PSL performance of Na₂CaGe₂O₆:Bi³⁺ is significantly superior to that of the non-doped sample. Accordingly, a multimode dynamic luminescent anticounterfeiting and encryption approach is successfully constructed, which could pave a new way for the design and development of sophisticated and effective anti-counterfeiting.

2. Results and discussion

The Na₂CaGe₂O₆ matrix possesses a trigonal structure with a space group Rm (no.166). The crystal structure of Na₂CaGe₂O₆ is illustrated in Fig. 1a, where Ge⁴⁺ ions are coordinated by eight oxygen ions in dodecahedral sites with the formation of the GeO₈ dodecahedron.^36,37 The Na⁺ and Ca²⁺ ions occupy the same position surrounded by 8 or 12 oxygen ions, named A1 (d_ave = 2.376 Å), A2 (d_ave = 2.434 Å), A3 (d_ave = 2.455 Å) and A4 (d_ave = 2.326 Å), respectively. The X-ray diffraction (XRD) patterns of the as-synthesized Na₂CaGe₂O₆:xBi³⁺ (x = 0, 0.002, 0.005, 0.010, and 0.020) samples are exhibited in Fig. 1b. It can be observed that all the diffraction peaks of the samples align well with the standard card of Na₂CaGe₂O₆ (PDF#011-3302), indicating the successful synthesis of pure phased samples. No impurity phases are detected when Bi³⁺ ions are doped into the Na₂CaGe₂O₆ matrix, confirming the successful incorporation of Bi³⁺ ions into the matrix. According to the Hume-Rothery rule³⁸ for the consideration of the valence state and the coordination number (CN), which takes into account the valence state and coordination number of the ions. The radius of Bi³⁺ ions (R = 1.17 Å, CN = 8) is slightly larger than that of the A1 sites (R_Na⁺ = 1.16 Å, R_Ca²⁺ = 1.12 Å, CN = 8). On the other hand, the twelve coordinated Na⁺/Ca²⁺ sites (R_Na⁺ = 1.39 Å, R_Ca²⁺ = 1.34 Å, CN = 12) are too large for Bi³⁺ ions to occupy. Additionally, previous studies^37,39,40 have shown that Yb²⁺, Tb³⁺, Er³⁺, and Ho³⁺ ions, which have similar atomic radii to Bi³⁺ ions, all occupy the A1 site. The main diffraction peak (2 2 0) at 33.2° shifts towards a lower angle along with the increased concentration of Bi³⁺ ions, indicating lattice expansion induced for the substitution of Bi³⁺ ions at A1 sites. The corresponding lattice parameters (a, b, c and V) increase linearly as depicted in Fig. S1,† further confirming that Bi³⁺ ions are incorporated successfully into the Na₂CaGe₂O₆ host, accordingly. The Rietveld refinement of Na₂CaGe₂O₆:0.002Bi³⁺ is shown in Fig. 1c, and the reliability parameters of the refinement are calculated to be R_p = 12.70% and R_wp = 9.93%, verifying the phase purity of the as-prepared samples. The scanning electron microscope (SEM) image of the as-obtained Na₂CaGe₂O₆:0.002Bi³⁺ sample as well as the corresponding element mapping are depicted in Fig. 1d, which manifests that the Na, Ca, Ge, O and Bi elements are uniformly distributed within the Na₂CaGe₂O₆ particle.

The photoluminescence excitation (PLE) and PL spectra of the Na₂CaGe₂O₆ phosphor are given in Fig. 2a. Under the excitation of 254 nm, the PL spectrum exhibits two distinct emission bands at 392 and 630 nm. The PLE spectrum of Na₂CaGe₂O₆, when monitoring the emission of 630 nm, displays a broad band ranging from 200 to 375 nm, peaking at 254 nm and 302 nm, respectively. In contrast, there is only one excitation peak at 302 nm is detected by monitoring the wavelength 392 nm. Furthermore, samples of Na₂CaGe₂O₆ were produced by sintering in the air (Na₂CaGe₂O₆:Air), and argon atmospheres (Na₂CaGe₂O₆:Argon), and Na_1.89Ca_0.96Ge₂O₆ was sintered in an air atmosphere (Na_1.89Ca_0.96Ge₂O₆:Air). The XRD patterns of these samples are presented in Fig. S2a.† All the diffraction peaks of the corresponding samples match well with those from the standard card of Na₂CaGe₂O₆ (PDF#011-3302), suggesting that the pure phase samples were successfully obtained. The PL spectra of these samples shown in Fig. S2b† display two identical self-activated emissions with two broad bands centered at 392 nm and 630 nm under 254 nm excitation. Compared with the sample sintered in air, the argon-sintered sample shows a significant increase in the emission intensity at 392 nm. Moreover, the emission intensity of the Na₂CaGe₂O₆:Air sample at 630 nm is significantly enhanced compared to that of Na_1.89Ca_0.96Ge₂O₆:Air. Herein, it is safe to say that the two emissions of the Na₂CaGe₂O₆ phosphor are closely related to the corresponding defects. Fig. 2b shows the O 1s orbital peak of the Na₂CaGe₂O₆:Air and Na₂CaGe₂O₆:Argon samples. The peak of the O 1s orbitals can be fitted with four Gaussian peaks. The high-energy component of the peak is mainly attributed to the loosely bound oxygen, while the two low-energy peaks indicate the presence of oxygen vacancies.^41–43 On the lower side of the binding energy, two peaks of the O 1s orbitals are distinguished and labeled as peak I (OI) and peak II (OII). The intensity ratios of OII and OI are associated with the concentration of oxygen vacancies and the highest ratio between OII and OI is observed for the Na₂CaGe₂O₆:Argon sample, suggesting that a higher number of oxygen vacancies are formed (Table S1†). It indicates that the self-activated band at 392 nm is related to the presence of oxygen vacancies. Moreover, the defect preference of Na_1.89Ca_0.96Ge₂O₆ was investigated through density functional theory (DFT) calculations.⁴⁴ Here, the possible substitution models for the vacancy (, M1) and inverse site (, M2) defects are considered. As shown in Fig. 2c, the formation energy of the M2 model was calculated to be −4.76 eV lower than that of the M1 model with −3.05 eV. It indicates that defects are more inclined to be formed, and the 630 nm emission is associated with defects. In addition, the formation energy of the oxygen vacancies was calculated to be −4.15 eV. From the point of view of charge neutrality, it is inferred that the negatively charged defects could be , which is located near the valence band, thereby facilitating electron–hole complexation during luminescence. Currently, much of the intrinsic emission of the self-activated fluorescent phosphor is attributed to intrinsic defects, as summarized in Table S2.†

Moreover, the PL spectra of the Na₂CaGe₂O₆:xBi³⁺ (x = 0, 0.002, 0.005, 0.010, and 0.020) phosphors show two distinct emission bands at 392 nm and 630 nm under the excitation of 254 nm, as shown in Fig. 2d. No additional emission bands are observed compared to that of the Na₂CaGe₂O₆ phosphor. Furthermore, the PLE spectrum of the Na₂CaGe₂O₆:Bi³⁺ phosphor is identical to that of the Na₂CaGe₂O₆ sample, as shown in Fig. S3.† These results suggest that the introduction of Bi³⁺ does not act as an emission center in the Na₂CaGe₂O₆ phosphor. The dependence of the concentration of Bi³⁺ ions on the luminescence intensity of the phosphor demonstrates that the Na₂CaGe₂O₆:0.002Bi³⁺ sample achieves the optimal luminescence intensity. Additionally, the relative emission intensities at 392 nm and 630 nm gradually change with the increase of the Bi³⁺ ions concentration, demonstrating that the incorporation of Bi³⁺ ions can effectively modulate the defect concentration in the Na₂CaGe₂O₆ matrix. The gradual change in the Commission Internationale de l'Eclairage (CIE) coordinates from (0.5412, 0.3547) to (0.3579, 0.2458), as shown in Fig. 2e, indicates a shift in the emission color from red to bluish violet light, which is matched well with the corresponding photographs.

Moreover, the decay curves of Na₂CaGe₂O₆ and Na₂CaGe₂O₆:Bi³⁺ obtained by monitoring the wavelength at 392 and 630 nm can be well fitted by double exponential functions (Fig. 2f):^45,46

	(1)

The average luminescence lifetime τ* can be acquired from the following equation:^47,48

	(2)

The average lifetime of Na₂CaGe₂O₆ and Na₂CaGe₂O₆:Bi³⁺ obtained by monitoring the emission at 392 nm is calculated to be 12.53 and 11.37 μs, respectively, moreover, by monitoring the emission at 630 nm, the calculated lifetime was determined to be 49.21 and 47.84 μs, respectively. The lifetime values of the corresponding emissions are similar before and after the introduction of the dopant ions, hence, it is safe to say that the introduction of Bi³⁺ contributes to the manipulation of the defect structure, rather than acting as activated centers.

The as-obtained Na₂CaGe₂O₆:0.002Bi³⁺ phosphor displays modulated PL properties, as evidenced by the gradual change in PL color from violet to red as the exposure time increases from 0 to 60 seconds under 254 nm UV irradiation (Fig. 3a). The corresponding time-dependent PL spectra of Na₂CaGe₂O₆:0.002Bi³⁺ phosphor are given in Fig. 3b. As the irradiation time increases, the emission intensity at 392 nm decreases while the emission intensity at 630 nm gradually increases. Consequently, the ratio of the emission intensity at 392 to 630 nm undergoes a significant change with increasing irradiation time, as depicted in Fig. 3c. The corresponding chromaticity coordinates successfully shift from (0.3284, 0.2369) to (0.4324, 0.2878) (Fig. 3d). Accordingly, the emission intensity of Na₂CaGe₂O₆ changes with increasing irradiation time (Fig. S4†). Compared with the counterpart sample doped with Bi³⁺ ions, it is shown that the introduction of Bi³⁺ ions regulates the intrinsic defects, showing obvious dynamic PL performance. Fig. 3e shows the time-resolved I_{392 nm}/I_{630 nm} ratio from 1 to 120 s, revealing the high repeatability of the obtained sample in terms of the dynamic PL behavior. In addition, the dynamic change of the emission intensity under different wavelength irradiations is shown in Fig. S5.† With the increase of irradiation wavelength, the increasing trend of emission intensity at 630 nm gradually decreases, while the decreasing trend of emission intensity at 392 nm gradually increases. The results show that the emission intensity at 392 and 630 nm follows the opposite trend under irradiation with different wavelengths, which may be caused by the two emissions associated with distinct trap centers.

The temperature performance of Na₂CaGe₂O₆:0.002Bi³⁺ was evaluated in the form of temperature-dependent PL spectra (80–270 K) shown in Fig. 4a. The emission intensities at 630 and 392 nm decrease gradually at the same rate as the temperature increases. When the temperature rises from 290 to 450 K, the thermal quenching rate of 630 nm emission is significantly higher than that of 392 nm, as shown in Fig. 4b. It is inferred that the distinct thermal response of the two involved emission centers is involved. Moreover, the PL spectra of the Na₂CaGe₂O₆:0.002Bi³⁺ sample recorded the emission of 630 nm showing an obvious blue shift with the increase of temperature, are depicted in Fig. 4c. The inset plots the emission peak position, which confirms a slightly continuous blue-shift of the emission from 630 nm to 609 nm. The expansion of the host lattice with temperature increase may cause a reduction in the crystal field splitting, which furthermore leads to higher energy for the emission.⁴⁹ As evidenced, the gradual change in PL color from red to violet as temperature increases from 80 to 450 K is presented in Fig. 4d. The variable-temperature spectra of Na₂CaGe₂O₆ samples are shown in Fig. S6,† the emission intensity of the sample gradually decreases, and is almost completely quenched at 450 K with the increase of temperature, while the emission intensity of the Na₂CaGe₂O₆:0.002Bi³⁺ sample maintains 40% of its initial value measured at 80 K. It indicates that the introduction of Bi³⁺ ions enhances the thermal stability of the corresponding sample.

Furthermore, the Na₂CaGe₂O₆:Bi³⁺ phosphor exhibits excellent optical storage capabilities, making it suitable for information encryption applications. Optical storage performance is known to depend on traps,^50–52 so thermoluminescence (TL) spectra of the corresponding sample with varying concentrations of Bi³⁺ ions were measured, as shown in Fig. 5a. The TL curves reveal a broad band centered at 360 K for all these samples, with a bandwidth ranging from 300 to 450 K, indicating a variety of trap depths and types. The density of the trap increases with the increased concentration of Bi³⁺ ions and reaches a maximum when the concentration of Bi³⁺ ions is 0.02. The TL curve exhibits a broad nonsymmetrical band, which can be accurately Gaussian-fitted into two bands located at 375 K (trap 1) and 415 K (trap 2), as shown in Fig. S7.† The number of trapped carriers as a function of irradiation time was studied using TL measurements (Fig. S8†). The integrated TL intensity is enhanced with increasing irradiation time and reaches saturation at ≈90 s. Meanwhile, the trap depth moves towards the high-temperature region from 335 to 367 K with increasing irradiation time. To further analyze the trap energy levels in detail, the optimized Na₂CaGe₂O₆:0.002Bi³⁺ sample was selected for further studies. Fig. 5b presents the TL spectra of Na₂CaGe₂O₆:0.002Bi³⁺ phosphor recorded at different preheated temperatures. It can be observed that the TL peak experiences a red shift as the initial temperature increases, indicating that a higher preheated temperature facilitates the faster release of carriers from shallow traps. The depths of the traps at different preheated temperatures are calculated by equations:^53,54

	(3)

where ω = δ + τ, and δ and τ are the high-temperature and the low-temperature half-width, respectively. The asymmetry parameter μ_g= δ/ω and k is the Boltzmann constant. T_m is the TL glow peak temperature. Accordingly, the depths of the corresponding traps were calculated to be 0.69, 0.71, 0.72, 0.76 and 0.78 eV (Fig. 5c). Moreover, the LPL and PSL spectra of Na₂CaGe₂O₆:0.002Bi³⁺ phosphor are explored, as shown in Fig. 5d. The identical spectral shape of LPL and PSL suggests that the luminescent behavior originates from identical emission centers. The emission intensity at 630 nm is higher than that of 392 nm, indicating that trap 2 captures a larger number of electrons. It should be noted that Na₂CaGe₂O₆ exhibits only weak PSL without any LPL performance (Fig. S9†). It indicates that the introduction of Bi³⁺ ions significantly increases the concentration of the traps, leading to the emergence of obvious LPL performance and enhanced PSL behavior. The LPL decay curves of Na₂CaGe₂O₆:0.002Bi³⁺ show similar decay rates of 392 nm and 630 nm emissions (Fig. 5e). The LPL decay curves of Na₂CaGe₂O₆:0.002Bi³⁺ are illustrated in Fig. S10,† revealing a gradual decay over a time scale of 300 s. The PSL decay curves of Na₂CaGe₂O₆:0.002Bi³⁺ are recorded by prolonging the irradiation time of 980 nm, as depicted in Fig. 5f. With the increased excitation time of 980 nm, the PSL intensity gradually decreases, indicating that the charged carriers captured at traps can be effectively released under 980 nm near-infrared (NIR) laser stimulation. The LPL and PSL photographs of the Na₂CaGe₂O₆:0.002Bi³⁺ sample recorded at a prolonged time are shown in Fig. 5g. After being charged by a 254 nm lamp for 60 s, the phosphor emits red afterglow and PSL performance.

Accordingly, the corresponding mechanism can be summarized as follows (Fig. S11†). Under 254 nm UV irradiation, the electrons in the valence band (VB) are excited to the conduction band (CB). A part of the electrons under un-radiative relaxation from CB to (trap 1) and (trap 2) levels. Subsequently, the PL emission is generated through the recombination of the excited state (trap 1 and trap 2) and ground state (VB), resulting in the emission peaks at 392 nm and 630 nm. The dynamic PL observed in Na₂CaGe₂O₆:0.002Bi³⁺ phosphor under 254 nm UV irradiation can be attributed to the presence of shallow and deep traps. When the electrons in the valence band are excited to the conduction band, a portion of them undergo non-radiative relaxation to (trap 1) and (trap 2) levels. Subsequently, the PL is generated through the recombination of the excited state (trap 1 and trap 2) and ground state, resulting in the emission peaks at 392 nm and 630 nm. At the beginning of the UV irradiation, the electrons in the CB are preferentially captured by trap 1 which is to be filled up instantly, leading to the emission of 392 nm. However, as the irradiation time increases, trap 1 is closer to the conduction band; the captured carriers are prone to thermal disturbance. This results in some of the captured electrons entering the conduction band, leading to a decrease in the intensity of the 392 nm. At the same time, the number of electrons captured by trap 2 increases, leading to an increase in the emission intensity at 630 nm. After the removal of UV irradiation, these trapped electrons escape from their respective traps under thermal perturbation or excitation by the 980 nm laser and then transition to the ground state, resulting in the generation of both LPL and PSL.

Based on the fascinating PL, LPL, and PSL properties of Na₂CaGe₂O₆, Na₂CaGe₂O₆:0.002Bi³⁺ and Na₂CaGe₂O₆:0.02Bi³⁺ phosphors, a multimode dynamic optical output for anti-counterfeiting and information encryption was constructed. Firstly, the luminescent patterns were fabricated by screen printing, as shown in Fig. 6a. Na₂CaGe₂O₆, Na₂CaGe₂O₆:0.002Bi³⁺ and Na₂CaGe₂O₆:0.02Bi³⁺ phosphors were employed to fill the patterns of “panda” and “flower”, respectively. Under UV irradiation, the “panda” patterns exhibit a remarkable PL. With the increase of the irradiation time, the pattern of the panda's face gradually changed from purple to red, while the pattern of the panda's body and flowers maintained the original purple and red, respectively. After UV irradiation for 60 s, the pattern of “panda” turned purple after the sample was heat-treated at 450 K. After tuning off the UV lamp for 1 s, only the “panda” pattern exhibited significant red afterglow. Because of the difference in the LPL decay rate between Na₂CaGe₂O₆:0.002Bi³⁺ and Na₂CaGe₂O₆:0.02Bi³⁺ phosphors, the full red “panda” could be observed within 30 seconds with the naked eye. A schematic diagram, describing the preparation of two quick response (QR) code patterns, is shown in Fig. 6b. Na₂CaGe₂O₆ and Na₂CaGe₂O₆:0.002Bi³⁺ phosphors are filled with two different QR codes, and then the two QR codes were superimposed on each other (Fig. 6b i). Here, once one of the QR codes is displayed completely and successfully scanned, the encrypted information can be read out. Moreover, once the Na₂CaGe₂O₆ and Na₂CaGe₂O₆:0.002Bi³⁺ are filled with different regions of the QR code (Fig. 6b ii), the encrypted information could be obtained as long as both of the involved phosphors perform identical decay time. Under 254 nm UV lamp excitation, the QR codes initially encompass the red and the violet patterns, and the emission is gradually dominated by the red light with the increase of irradiation time, wherein the encrypted information was unreadable, as shown in Fig. 6c i. After the ultraviolet lamp was turned off after 60 s, a clear and complete red QR code was observed in the LPL mode and the information “CDU” can be read successfully within 20 seconds. However, the information cannot be read out in the PSL mode. In Fig. 6c ii, the QR code information “CDU” can be recognized only with the PL and PSL modes. According to the results, the multi-modal dynamic optical information encryption and decoding strategy is available for effectively improving information security in anti-counterfeiting applications.

3. Conclusions

In summary, the multi-mode dynamic luminescent behavior of Na₂CaGe₂O₆:Bi³⁺ was evaluated. The emission at 392 and 630 nm of the Na₂CaGe₂O₆ matrix was proved to be closely related to the defects of and . Moreover, the color of the corresponding sample changes significantly from purple to red with the increase of irradiation time, thanks to the incorporation of Bi³⁺. Moreover, the incorporation of Bi³⁺ promotes the enhancement of the density of and traps, leading to the improvement of the dynamic PL performance and its thermal stability, as well as the LPL and PSL behavior. Accordingly, a multi-mode dynamic optical output for anti-counterfeiting and information encryption with the as-explored self-activated phosphor is achieved.

Data availability

The data supporting this article have been included as part of the ESI.†

Conflicts of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was financially supported by the National Nature Science Foundation of China (NSFC) (1220041913, U2241236), the Sichuan Natural Science Foundation (2022JDJQ0030), and the Science Fund of Shandong Laboratory of Advanced Materials and Green Manufacturing at Yantai (AMGM2024F15).

References

1. D. Gao, J. Gao, F. Gao, Q. Kuang, Y. Pan, Y. Chen and Z. Pan, J. Mater. Chem. C, 2021, 9, 16634–16644 RSC .
2. H. Guo, T. Wang, X. Zhu, H. Liu, L. Nie, L. Guo, T. Gu, X. Xu and X. Yu, J. Colloid Interface Sci., 2023, 640, 719–726 CrossRef CAS PubMed .
3. K. Jiang, C. Zhou, W. Li, H. Su, D. He, X. Chen, D. Zhang, S. Xie and R. Yu, J. Alloys Compd., 2024, 980, 173518 CrossRef CAS .
4. H. Yang, W. Zhao, E. Song, R. Yun, H. Huang, J. Song, J. Zhong, H. Zhang, Z. Nie and Y. Li, J. Mater. Chem. C, 2020, 8, 16533–16541 RSC .
5. L. Li, T. Li, Y. Hu, C. Cai, Y. Li, X. Zhang, B. Liang, Y. Yang and J. Qiu, Light: Sci. Appl., 2022, 11, 51 CrossRef CAS PubMed .
6. T. Lyu, P. Dorenbos, C. Li, S. Li, J. Xu and Z. Wei, Chem. Eng. J., 2022, 435, 135038 CrossRef CAS .
7. Y.-L. Yang, T. Li, F. Guo, J.-Y. Yuan, C.-H. Zhang, Y. Zhou, Q.-L. Li, D.-Y. Wan, J.-T. Zhao and Z.-J. Zhang, Inorg. Chem., 2022, 61, 4302–4311 CrossRef CAS PubMed .
8. Z. Li, Z. Lyu, P. Luo, S. Wei, C. Zhuo, D. Sun, S. Shen and H. You, Inorg. Chem. Front., 2023, 10, 6746–6753 RSC .
9. Y. Li, W. You, J. Zhao, X. Zhang, G. Pan, P. Liu and Y. Mao, J. Mater. Chem. C, 2023, 11, 546–553 RSC .
10. F. Men, T. Hu, Z. Jiang, H. Yang, Y. Gao and Q. Zeng, Inorg. Chem., 2023, 63, 668–676 CrossRef PubMed .
11. K. Shwetabh, A. Banerjee, R. Poddar and K. Kumar, J. Alloys Compd., 2024, 980, 173493 CrossRef CAS .
12. B.-M. Liu, X.-X. Guo, L.-Y. Cao, L. Huang, R. Zou, Z. Zhou and J. Wang, Chem. Eng. J., 2023, 452, 139313 CrossRef CAS .
13. P. Lin, J. Shi, L. Liu, Y. Kang, L. Song, M. Hong and Y. Zhang, Inorg. Chem. Front., 2023, 10, 5178–5185 RSC .
14. C. Wang, Y. Jin, J. Zhang, X. Li, H. Wu, R. Zhang, Q. Yao and Y. Hu, Chem. Eng. J., 2023, 453, 139558 CrossRef CAS .
15. J. Du, A. Feng and D. Poelman, Laser Photonics Rev., 2020, 14, 2000060 CrossRef CAS .
16. T. Si, Q. Zhu, T. Zhang, X. Sun and J.-G. Li, Chem. Eng. J., 2021, 426, 131744 CrossRef CAS .
17. Z. Li, J. Xiang, C. Chen, Z. Wu, M. Jin, X. Zhao, L. Zhao and C. Guo, J. Mater. Chem. C, 2024, 12, 5727–5736 RSC .
18. X. Zhang, S. Han, G. Lian, D. Cui and Q. Wang, CrystEngComm, 2023, 25, 5533–5540 RSC .
19. J. Sang, J. Zhou, J. Zhang, H. Zhou, H. Li, Z. Ci, S. Peng and Z. Wang, ACS Appl. Mater. Interfaces, 2019, 11, 20150–20156 CrossRef CAS PubMed .
20. X. Zhu, T. Wang, Z. Liu, Y. Cai, C. Wang, H. Lv, Y. Liu, C. Wang, J. Qiu, X. Xu, H. Ma and X. Yu, Inorg. Chem., 2022, 61, 3223–3229 CrossRef CAS PubMed .
21. Q. He, Y. Yan, T. Wang, L. Guo, Y. Yue, N. Zhu, W. Bu, X. An, B. Duan, X. Zhu and X. Yu, CrystEngComm, 2024, 26, 2096–2102 RSC .
22. Z. Sun, J. Yang, L. Huai, W. Wang, Z. Ma, J. Sang, J. Zhang, H. Li, Z. Ci and Y. Wang, ACS Appl. Mater. Interfaces, 2018, 10, 21451–21457 CrossRef CAS PubMed .
23. J. Zhang, Z. Wang, X. Huo, Y. Wang and P. Li, Inorg. Chem. Front., 2022, 9, 6517–6526 RSC .
24. D. Gao, Q. Kuang, F. Gao, H. Xin, S. Yun and Y. Wang, Mater. Today Phys., 2022, 27, 100765 CrossRef CAS .
25. Y. Xiao, P. Xiong, S. Zhang, K. Chen, S. Tian, Y. Sun, P. Shao, K. Qin, M. G. Brik, S. Ye, D. Chen and Z. Yang, Chem. Eng. J., 2023, 453, 139671 CrossRef CAS .
26. T. Lyu, P. Dorenbos and Z. Wei, Chem. Eng. J., 2023, 461, 141685 CrossRef CAS .
27. X. Chen, Y. Pan, Y. Ding, H. Lian, J. Lin and L. Li, Inorg. Chem., 2024, 63, 3525–3534 CrossRef CAS PubMed .
28. M. Zhao, Z. Yang, L. Ning and Z. Xia, Adv. Mater., 2021, 33, 2101428 CrossRef CAS PubMed .
29. L. Wang, C. Wang, Y. Chen, Y. Jiang, L. Chen, J. Xu, B. Qu and H. T. Hintzen, Chem. Mater., 2022, 34, 10068–10076 CrossRef CAS .
30. R. Hu, Y. Zhao, Y. Zhang, X. Wang, G. Li and M. Deng, Appl. Mater. Today, 2022, 26, 101376 CrossRef .
31. J. Du, S. Lyu, P. Wang, T. Wang and H. Lin, Adv. Opt. Mater., 2023, 11, 2300359 CrossRef CAS .
32. J. Jia, X. Gao and G. Zou, Adv. Funct. Mater., 2022, 32, 2207881 CrossRef CAS .
33. C. H. Ahn, Y. Y. Kim, D. C. Kim, S. K. Mohanta and H. K. Cho, J. Appl. Phys., 2009, 105, 013502 CrossRef .
34. P. Liu, Z. Yi, B. Li, Z. Xia and Y. Xu, Adv. Opt. Mater., 2024, 12, 2303038 CrossRef CAS .
35. Z. Yang, S. Lai and Z. Xia, J. Solid State Chem., 2020, 288, 121408 CrossRef CAS .
36. X. Y. Jin, Z. Y. Wang, H. Y. Xu, M. C. Jia and Z. L. Fu, Mater. Today Chem., 2022, 24, 100771 CrossRef CAS .
37. J. Wang, J. Ma, J. Zhang, Y. Fan, W. Wang, J. Sang, Z. Ma and H. Li, ACS Appl. Mater. Interfaces, 2019, 11, 35871–35878 CrossRef CAS PubMed .
38. W. Hume-Rothery, Contemp. Phys., 1964, 5, 321–347 CrossRef CAS .
39. X. Jin, Z. Wang, Y. Wei and Z. Fu, J. Lumin., 2022, 249, 118937 CrossRef CAS .
40. Z. Ma, S. Tian, H. Wu, J. Zhang and H. Li, Ceram. Int., 2018, 44, 14582–14586 CrossRef CAS .
41. X. Zhu, X. Yu, W. Gao, H. Liu, L. Nie, H. Guo, F. Zhao, S. Yu and T. Wang, Chem. Eng. J., 2022, 442, 136235 CrossRef CAS .
42. Y. Wei, G. Xing, K. Liu, G. Li, P. Dang, S. Liang, M. Liu, Z. Cheng, D. Jin and J. Lin, Light Sci. Appl., 2019, 8, 15 CrossRef PubMed .
43. E. Pavitra, L. Antony, K. S. Ranjith, K. Alotaibi, J.-H. Lee, S. K. Hwang, G. S. R. Raju, Y.-K. Han and Y. S. Huh, J. Alloys Compd., 2024, 979, 173574 CrossRef CAS .
44. J. Xiang, X. Zhou, X. Zhao, Z. Wu, C. Chen, X. Zhou and C. Guo, Laser Photonics Rev., 2023, 17, 2200965 CrossRef CAS .
45. D. Stefańska and P. J. Dereń, Adv. Opt. Mater., 2020, 8, 2001143 CrossRef .
46. S.-Y. Zhu, D. Zhao, S.-J. Dai, R.-J. Zhang and L.-Y. Shi, CrystEngComm, 2022, 24, 2966–2975 RSC .
47. S. Wu, P. Xiong, X. Liu, Y. Fu, Q. Liu, M. Peng, Y. Chen and Z. Ma, J. Mater. Chem. C, 2020, 8, 16584–16592 RSC .
48. L. Zhou, R. Chen, X. Jiang, T. Zhang, X. Shi, Z. Leng, Y. Yang, Z. Zhang, C. Zuo, C. Li, W. Yang, H. Lin, L. Liu, S. Li, F. Zeng and Z. Su, Inorg. Chem., 2024, 63, 1274–1287 CrossRef CAS PubMed .
49. D.-Y. Wang, Z.-B. Tang, W. U. Khan and Y. Wang, Chem. Eng. J., 2017, 313, 1082–1087 CrossRef CAS .
50. H. Song, R. Zhang, Z. Zhao, X. Wu, Y. Zhang, J. Wang and B. Li, ACS Appl. Mater. Interfaces, 2022, 14, 45562–45572 CrossRef CAS PubMed .
51. D. Van der Heggen, J. J. Joos, A. Feng, V. Fritz, T. Delgado, N. Gartmann, B. Walfort, D. Rytz, H. Hagemann, D. Poelman, B. Viana and P. F. Smet, Adv. Funct. Mater., 2022, 32, 2208809 CrossRef CAS .
52. M. Li, Y. Jin, L. Yuan, B. Wang, H. Wu, Y. Hu and F. Wang, ACS Appl. Mater. Interfaces, 2023, 15, 13186–13194 CrossRef CAS PubMed .
53. L. Guo, T. Wang, Q. Wang, W. Feng, Z. Li, S. Wang, P. Xia, F. Zhao and X. Yu, Chem. Eng. J., 2022, 442, 136236 CrossRef CAS .
54. L. Li, K.-L. Wong, P. Li and M. Peng, J. Mater. Chem. C, 2016, 4, 8166–8170 RSC .

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Footnote

† Electronic supplementary information (ESI) available: The experimental approach, characterizations and computational methodology. See DOI: https://doi.org/10.1039/d4ce00578c

This journal is © The Royal Society of Chemistry 2024