Hang Liu,Zhi Ye,Ding Sun,Lixin Zhang,Xueyan Lv,Wentong Cai,Yuhong Zhang
Rear earth(RE)-doped halide perovskite has generated as an amazing optical material for multicolor luminescence. Free-lead halide double perovskites have attracted interesting because of their non-toxicity and higher instability. Here, RE 3+ doped chloride-based double perovskite phosphors are reported. A series of heavy concentration Ho 3+ /Yb 3+ doped Cs 2 NaBiCl 6 (CNBC) phosphors are prepared with a solvothermal route. The band structure of CNBC is calculated through density functional theory (DFT). The luminescence properties of CNBC:Ho 3+ and CNBC:Ho 3+ /Yb 3+ are investigated through upconversion(UC) and downshifting(DS) processes. From CNBC:Ho 3+ , the brightness orange, deep red and pale green lights are achieved under excitation at 365, 452 and 980 nm. The multicolor emissions of CNBC:Ho 3+ are used to multimode fluorescent anti-counterfeiting. Comparing with CNBC:Ho 3+ samples, the UC emission intensity of CNBC:Ho 3+ /Yb 3+ are dramatically enhanced. The brightness green light can be seen by naked eyes under super lower power pumping(∼10 mW). The temperature sensing properties of CNBC:Ho 3+ /Yb 3+ phosphor are investigated systematically based on the luminescence intensity ratio(LIR) of thermally coupled levels(TCLs)( 5 F 1 / 5 G 6 , 5 F 2,3 / 3 K 8 ) and non-TCLs( 5 F 4 / 5 S 2 , 5 F 5 ). The maximum relative sensitivity(S R ) reaches 5.089% K −1 at 293 K according to the LIR of non-TCLs. The work will broaden the application field of RE 3+ -doped free-lead perovskite such as anti-counterfeiting and thermometry.
A series of Y 2 O 2 S: 0.25 % Ho 3+ /x%Yb 3+ (where x = 4, 6, 8, and 10) phosphors were synthesized by using a chemical co-precipitation method, and their temperature sensing properties were systematically investigated. The upconversion luminescence (UCL) spectra of the samples were recorded under 980 nm laser excitation. The Y 2 O 2 S: Ho 3+ /Yb 3+ system exhibits three distinct UC emission bands in the green, red, and near-infrared regions, corresponding to the transitions of 5 F 4 / 5 S 2 → 5 I 8 , 5 F 5 → 5 I 8 , and 5 F 4 / 5 S 2 → 5 I 7 of Ho 3+ , respectively. According to the emission spectra, the sample with a Yb 3+ doping concentration of 6 % exhibited the strongest luminescence intensity, with a quantum yield reaching 4.01 %. To further explore its temperature sensing properties, the fluorescence intensity ratios (FIR) of both thermally coupled energy levels (TCLs) and non-thermally coupled energy levels (NTCLs) of Ho 3+ were systematically analyzed. Notably, temperature sensing materials based on NTCLs exhibit significantly enhanced sensitivity while maintaining a broad temperature measurement range. Specifically, the absolute sensitivity (S A ) increased from 0.011 % to 0.498 %, representing an approximately 45-fold improvement. These findings indicate that Y 2 O 2 S: Ho 3+ /Yb 3+ UCL materials possess excellent potential for applications in optical temperature sensing.
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