Structural Transformation and Photoluminescent Property of Manganese-Doped Bismuth-Based Perovskites

The structural transition from Mn-dopedCs(3)Bi(2)Cl(9) (CBCM) to Cs4MnBi2Cl12 (CMBC) can be controlled by changingthe concentration ofMn(2+). The PL emission blue-shifts after the structuraltransition, and a model for the wavelength change of the emissionis proposed. The PL lifetime property of CMBC is applied to a widerange of temperature measurements. Here, we synthesized pure Cs3Bi2Cl9 (CBC) and manganese (Mn)-doped crystals with differentfeeding ratios,leading to changes in structure and luminescence. The crystals Cs3Bi2Cl9-Mn (CBCM) formed by dopinga minor amount of Mn2+ (Bi/Mn = 8:1) maintain the orthorhombicphase structure of the host, but when Bi/Mn = 2:1, the crystal structureis more inclined to form Cs4MnBi2Cl12 (CMBC) of a trigonal phase. Combined with density functional theory(DFT) calculation, the results demonstrate that a moderate amountof Mn2+ doping can create impurity energy levels in theforbidden band. However, as the structure transitions, the type ofenergy band structure changes from indirect to direct, with completelydifferent electronic orbital features. Temperature-dependent time-resolvedand steady-state photoluminescence spectroscopies are used to explorethe structure-related thermal properties and transitional process.Differences energy transfer routes are revealed, with CBCM relyingon intersystem energy transfer and CMBC mainly depending on directexcitation 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 maximumrelative sensitivity of 1.7 %K-1 and an absolutesensitivity of 0.0099 K-1. Our work provides insightinto the mechanism of Mn2+ doping-induced luminescenceand offers a potentially effective doping strategy for improving thePL properties of lead-free metal halide perovskites.