Development of Multifunctional Materials Based on Heavy Concentration Er3+-Activated Lead-free Double Perovskite Cs2NaBiCl6

Lead halide perovskites have been very promising for versatile optoelectronic applications, whereas the inherent toxicity and instability of lead halide restrict its wide application. Herein, a kind of high-performance multifunctional phosphor is designed based on heavy concentration Er 3+ -activated lead-free double perovskite Cs 2 NaBiCl 6 (CNBC), which realizes the self-sensitization of Er 3+ ions and emits high-brightness pure green emission upon dual near-infrared (dual-NIR) excitation. The luminescence properties can be further optimized by adding sensitizers (Yb 3+ /Nd 3+ ). Interestingly, the emission intensity of the green region is heightened by 212-fold after Yb 3+ ions doping, which is 40 times higher than that of the current popular phosphors (α-NaYF 4 :2%Er 3+ ,18%Yb 3+ ). Meanwhile, the temperature sensing properties of the thermally coupled levels (Er 3+ : 2 H 11/2 , 4 S 3/2 ) in Cs 2 NaBiCl 6 :40%Er 3+ are also investigated systematically based on the luminescence intensity ratio principle, and the maximum relative sensitivity is calculated to be as high as 1.27% K -1 (980 nm) and 1.57% K -1 (808 nm). Fortunately, the thermal stability and the performance for temperature readout of the studied phosphors are still maintaining a high level after doping sensitizers. The insights provided by this work will broaden the scope of lead-free halide double perovskites in the fields of luminescence and thermometry.