ИСТИНА

The aim of this research was to study the effect of solid-solution formation on the luminescence properties of concentration series of MAPbxHg1-xBr3, with x takes the value 1, 0.9, 0.75 and 0.5 (MA = CH3NH3 - methyl ammonium) in view of their possible application as scintillators. The single crystals were grown using antisolvent vapor-assisted crystallization method. Synchrotron radiation was used for luminescence excitation at the FinEstBeAMs station of the MAXIV storage ring (UV and VUV excitation spectra, temperature range 7-300 K), Lund, Sweden, and P23 station of the PETRA III storage ring (X-Ray excitation spectra, temperature range 80-300 K) of the German center for synchrotron radiation DESY, Hamburg, Germany. Time-resolved luminescence spectra, luminescence kinetics, temperature dependences of luminescence and kinetics spectra were measured using the unique features of synchrotron radiation. The fast luminescence band of free excitons [1] with a maximum at ~ 2.25 eV at 80K, was split into at least two subbands in the samples with x=0.9 and 0.75. This was attributed to disorder in cation spatial distribution in these systems. On the contrary, in the spectra of MAPbBr3 and MAPb0.5Hg0.5Br3 a single luminescence band associated with the exciton was observed indicative of a higher ordering of the structure with the equal concentration of Br and Hg. Comparison of the luminescence spectra upon VUV excitation and X-ray excitation made it possible to separate surface defects from the bulk ones and to reveal the role of reabsorption of exciton emission. In a series of solid solutions, a shift of the exciton peak was observed depending on the concentration of mercury in the sample by ~ 0.02 eV, which was attributed to the narrowing of the band gap with mercury content. The kinetics of exciton luminescence was nonexponential with a high contribution of the fast component with a characteristic decay time of less than 100 ps. This fact makes the studied perovskites promising scintillators in agreement with earlier research [2]; however, upon irradiation with high-density VUV radiation, the formation of new defects was observed. Radiation hardness of hybrid perovskites is a recognized issue and researches are working in this direction.