Luminescence thermometry has garnered significant attention due to its rapid response and non-invasive nature. For practical multimodal thermometry that requires high sensitivity and anti-interference capability, single-system materials with high emission intensity are highly desirable. Herein, we report a three-mode optical thermometric material based on La3Mg2NbO9:Er3+, a double perovskite phosphor that exhibits intense green emissions centered at 527 and 547 nm under either 378 nm or 980 nm excitation. Co-doping with Yb3+ significantly enhances the up-conversion (UC) luminescence intensity of Er3+ by a factor of 3 and increases its down-conversion (DC) luminescence intensity by 5-fold. Furthermore, this phosphor demonstrates temperature-dependent sensitivity across UC luminescence, DC luminescence, and fluorescence lifetime modes. Thermometric performance evaluated via the fluorescence intensity ratio of the thermally coupled levels (2H11/2 and 4S3/2) of Er3+ reveals outstanding behavior in both DC and UC modes over a broad temperature range (298–573 K), achieving maximum relative sensitivities of 1.16 % K−1 and 1.19 % K−1, respectively. The fluorescence lifetime mode yields a maximum absolute sensitivity of 36.42 % μs K−1. With excellent temperature sensitivity across all three modes, La3Mg2NbO9:Er3+ exhibits considerable potential for applications in self-referenced optical thermometry.

In the field of solid-state luminescence, Cu²⁺ has long been widely acknowledged for its capacity to emit infrared light. However, the occurrence of visible emission from Cu²⁺ ions had been infrequently observed and reported. In this study, we made an intriguing discovery by examining the behavior of Cu²⁺ within an irregular coordination environment of Ba in BaGa₂O₄. When excited by UV light, Cu²⁺ unexpectedly gave a vibrant yellow–red emission, covering a wavelength range spanning from 500 to 750 nm. More noteworthy, by simply manipulating the excitation wavelength or adjusting the temperature, the peak wavelength of the emission could be effectively tuned from approximately 600 to 660 nm, which could be attributed to the luminescence nature of the charge transfer (CT) between O²⁻ and Cu²⁺. Moreover, the phosphor material displayed a remarkable persistent luminescence (PerL) lasting up to 12 h after UV light excitation. Through thermoluminescence (TL) measurements and first-principle calculations, we found that the intrinsic defects, such as vacancies of oxygen and gallium (V_O and V_Ga^″), played important roles for the PerL phenomena. These findings highlighted the exceptional tunability and PerL properties of BaGa₂O₄:Cu²⁺. Our study provided a new potential guideline for the design of Cu²⁺-activated phosphors in visible region, and opened up new avenues for the research in related functional luminescence materials.

The red afterglow of current rare-earth-activated long persistent luminescence (LPL) phosphors is largely still less than 6 h, in contrast to the 20 or 30 h long blue- or green-emitting ones, becoming the main obstacle to realize their multiscenario applications in practice. Herein, we report a rare-earth-free red-emitting LPL phosphor SrGa₂O₄:Cu²⁺that can exhibit an afterglow at about 622 nm lasting over 30 h, which can largely match with the luminance of current blue- or green-emitting LPL phosphors. We find that the Cu²⁺ion could be charged by ultraviolet light from 280 to 420 nm, and the emission has a very broad band with a full width at half-maximum of about 150 nm. Combining the thermoluminescence measurement and the first-principles calculation, we find that the O vacancies and the -1 charged Ga vacancies could store the holes and contribute to the LPL of SrGa₂O₄:Cu²⁺. Our results may dramatically promote and expand its potential applications and stimulate the research of the multicolor LPL phosphors in future.

How the 3d transition metal (TM) ions induce defect levels in wide band gap compounds and how these defect levels evolve from compound to compound is very important in understanding and predicting the luminescent properties of TM activated phosphors. This issue is discussed by studying the ground state 3dⁿ level locations of the TM impurity ions (Sc-Zn) incorporated at the octahedral sites of many oxides. These ground state 3dⁿ level locations are obtained by collecting the CT bands from the literature of the past 50 years and also by first-principles calculations. By taking the vacuum level as the reference, we scaled all the locations of the TM ion in 3+ and 2+ states and constructed a zig-zag-curve scheme in α-Al₂O₃ through connecting the 3dⁿ ground state energies of Sc to Zn. The scheme can be extended to other aluminates easily and so offers a first estimate on where TM levels are located in compounds without complicated theoretical calculations. The estimate can be improved to a higher accuracy if the position of the valence band is known. Our work provides new insights for understanding the luminescent behavior of 3d-TM doped phosphors and may aid in developing 3d ion doped functional materials further.