Tingting Yan,Linan Liu,Dongyang Xi,Lei Sun,Dinghan Jin,Han Li
Cs2NaHoCl6, a double perovskite material, has demonstrated extensive application potential in the fields of anti-counterfeiting and optoelectronics. The synthesis of Cs2NaHoCl6crystals was achieved using a hydrothermal method, followed by the determination of their crystal structures through single crystal X-ray diffraction techniques. The material exhibits bright red fluorescence when exposed to ultraviolet light, confirming its excellent optical properties. An in situ high-pressure fluorescence experiment was conducted on Cs2NaHoCl6up to 10 GPa at room temperature. The results indicate that the material possibly undergoes a structural phase transition within the pressure range of 6.9–7.9 GPa, which is accompanied by a significant enhancement in fluorescence. Geometric optimization based on density functional theory (DFT) revealed a significant decrease in the bond lengths and crystal volumes of Ho-Cl and Na-Cl across the predicted phase transition range. Furthermore, it was observed that the bond lengths of Na-Cl and Ho-Cl reach an equivalent state within this phase transition interval. The alteration in bond length may modify the local crystal field strength surrounding Ho3+, consequently affecting its electronic transition energy levels. This could be the primary factor contributing to the structural phase transition.
Dual-band near-infrared (NIR) phosphors simultaneously covering the NIR-I (700-1000 nm) and NIR-II (1000-1700 nm) windows are highly desirable for practical optoelectronic devices, yet conventional rare-earth doped systems typically rely on ultraviolet sensitization. Herein, we report Yb 3+ /Er 3+ co-doped Cs 2 NaHoCl 6 double perovskite microcrystals (MCs) synthesized via a green aqueous-phase evaporation method, in which the intrinsic ∼450 nm absorption of Ho 3+ serves as a self-sensitizer, enabling competitive energy transfer from Ho 3+ to Yb 3+ and Er 3+ , predominantly via dipole-dipole interactions. This generates efficient dual-band emissions at 985 nm (NIR-I) and 1540 nm (NIR-II), with a high photoluminescence quantum yield (PLQY) of 85.6% under blue-light excitation, alongside excellent thermal stability and photostability. An NIR phosphor-converted light-emitting diode (pc-LED) fabricated with the optimized phosphor demonstrates practical utility in night vision, non-destructive detection, and high-contrast biological imaging. This work establishes an eco-friendly route for mass-producing efficient dual-band NIR emitters directly compatible with commercial blue LED chips.
Lead-free halide double perovskites (DPs) have attracted growing attention owing to their eco-friendly composition and remarkable optoelectronic performance. However, it remains a challenge to develop DPs that simultaneously achieve high photoluminescence quantum yield (PLQY), excellent stability, and multifunctional applications. Herein, rare-earth-based DPs Cs 2 NaHoCl 6 single crystals are successfully synthesized, which achieve the optimized red and near-infrared (NIR) emissions of Ho 3+ through doping Ce 3+ ions. Benefiting from strong absorption of Ce 3+ and efficient energy transfer to Ho 3+ under 340 nm excitation, the PLQY remarkably increases from 3.67% to 92.56%, which are confirmed by experimental analyses and density functional theory calculations. Meanwhile, taking advantage of abnormal anti-thermal quenching luminescence of Ho 3+ and highly efficient thermal response capability of Stark levels of 5 F 5 within the temperature range of 80–500 K, the prepared DPs provide a distinctive platform for luminescence thermometer with a superior relative sensitivity value of 5.19% K −1 at 80 K and red-NIR light-emitting diode. These results not only establish Ce 3+ as a generalizable strategy for optimizing luminescence in rare-earth-based DPs, but also open new avenues for their multiple potential applications in solid-state lighting, temperature sensing, night vision imaging as well as plant growth illuminating.
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