Optical spectroscopy of inorganic lead halide perovskite CsPbBr$_3$ single crystals

The paper presents the results of the temperature dependences study of the luminescence spectra (3.6 – 120 K) upon excitation by 405 nm light and of the non-contact measured photoconductivity spectra (3.6 – 300 K) of a CsPbBr$_3$ single crystal. In the low-temperature photoluminescence (PL) spectrum, in addition to the self-trapped exciton line (2.318 eV at 10 K), a rich structure, possibly related to exciton-impurity complexes, and a broad band with a maximum at about 2.24 eV, which may be the PL of impurity or defect centers, are observed. The photoconductivity (PC) spectrum contains two narrow peaks at the frequencies of intense excitonic PL lines and a wide continuum corresponding to band-to-band absorption. While PL quenches with increasing temperature, PC signal increases. Based on the analysis of the temperature dependences of the integral intensities of the exciton peak in the PL and PC, the activation energies of 12 $\pm$ 3 meV and 77 $\pm$ 10 meV were found for the processes leading to the decay of the self-trapped exciton, accompanied by the quenching of PL and the appearance of charge carriers,. An estimate of the exciton binding energy in a CsPbBr$_3$ single crystal was obtained: E$_b$ = 65 $\pm$ 13 meV.