A simple and rapid grinding method for preparing Er 3+ -doped and Er 3+ /Yb 3+ co-doped Cs 3 Bi 2 Cl 9 upconversion phosphors was developed. We avoid to employ strong acids as reaction solvents, aligning with the principles of green chemistry. By controlling the thermal treatment temperature and adding BiCl 3 , a reversible phase transformation process between Cs 3 Bi 2 Cl 9 and Cs 3 BiCl 6 perovskite phosphors was achieved. The Er 3+ /Yb 3+ co-doped Cs 3 Bi 2 Cl 9 phosphors emit green light under 980 nm excitation, whereas Cs 3 BiCl 6 phosphors emit red light. Their temperature sensing performance was tested through variable-temperature processes. Compared to Er 3+ -doped Cs 3 Bi 2 Cl 9 phosphors, the co-doped Er 3+ /Yb 3+ phosphors have a higher relative sensitivity of 1.60 % K −1 . Compared to previously reported materials, Cs 3 Bi 2 Cl 9 phosphors show enhanced sensitivity in temperature sensing. The study demonstrates that lead-free halide perovskites’ unique color-tunability not only underscores the innovativeness of this synthetic strategy but also provides a significant technological foundation for temperature sensing applications. Given their environmental friendliness and facile preparation process, these phosphors possess notable advantages for industrial production and hold promise as potential candidates for next-generation high-performance phosphor materials.
Here, we synthesized pure Cs3Bi2Cl9 (CBC) and manganese (Mn)-doped crystals with different feeding ratios, leading to changes in structure and luminescence. The crystals Cs3Bi2Cl9–Mn (CBCM) formed by doping a minor amount of Mn2+ (Bi/Mn = 8:1) maintain the orthorhombic phase structure of the host, but when Bi/Mn = 2:1, the crystal structure is more inclined to form Cs4MnBi2Cl12 (CMBC) of a trigonal phase. Combined with density functional theory (DFT) calculation, the results demonstrate that a moderate amount of Mn2+ doping can create impurity energy levels in the forbidden band. However, as the structure transitions, the type of energy band structure changes from indirect to direct, with completely different electronic orbital features. Temperature-dependent time-resolved and steady-state photoluminescence spectroscopies are used to explore the structure-related thermal properties and transitional process. Differences energy transfer routes are revealed, with CBCM relying on intersystem energy transfer and CMBC mainly depending on direct excitation of Mn2+ to produce d–d transitions. Furthermore, since CMBC is temperature-sensitive, we perform the first photoluminescent (PL) lifetime temperature measurement using CBMC and obtain a maximum relative sensitivity of 1.7 %K–1 and an absolute sensitivity of 0.0099 K–1. Our work provides insight into the mechanism of Mn2+ doping-induced luminescence and offers a potentially effective doping strategy for improving the PL properties of lead-free metal halide perovskites.
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