Large Spectral Shift of Mn Emission Due to the Shrinkage of the Crystalline Host Lattice of the Hexagonal CsCdCl Crystals and Phase Transition.

All-inorganic halide perovskite crystals are considered excellent optical host lattices for various dopants to obtain wavelength-tunable emissions with ultra-broad bands even over a wide spectral range. Here, a series of Mn-doped bulk ligand-free CsCdCl (CCC) perovskite crystals with a hexagonal shape and size of about 1 millimeter (mm) have been prepared by a facile hydrothermal method. These CCC:Mn (CCC:Mn) crystals emit the representative orange-red photoluminescence (PL) of Mn (T(G)-A(S)) in the centers of hexagonal octahedrons coordinated with six Cl ions. A fine-tuning of the Mn concentration from 1 to 50 mol % Cd induces a substantial red shift of emission spectra from 570 to 630 nm due to the shrinkage of the crystalline host lattice, and the maximum intensity of emission is achieved at 20 mol % Mn doping. A further increase in the Mn concentration causes a decrease of the PL intensity due to the phase transition from CCC to CsMnCl·2HO (CMCH). The strong excitation bands at 360, 370, 420, and 440 nm can make the excitation of the emissive CCC:Mn crystals possible with ultraviolet (UV) and blue chips for application in white light-emitting diodes (WLEDs). The similarity of the Mn-concentration-dependent emission spectra excited by various wavelengths indicates that there is only one type of site for Mn occupation in CCC.