Spectroscopic and vibrational properties of CsI single crystals doped with divalent samarium

Abstract

For the first time, a CsI:Sm²⁺ single crystal was successfully grown using the Kyropoulos method. Spectroscopic studies and theoretical calculations were conducted to characterize the crystal. The luminescence spectra and their temperature dependencies were investigated, revealing that the CsI:Sm²⁺ crystal contains at least two distinct types of radiative centers with differing Sm²⁺ ion environments. At room temperature, the crystal exhibits broad-band luminescence attributed to parity-allowed interconfigurational 4f⁵5d¹→4f⁶ transitions of Sm²⁺. At lower temperatures, sharp emission lines corresponding to 4f⁶→ 4f⁶ transitions emerge, while the 4f⁵5d¹→4f⁶ luminescence bands undergo a redshift due to strong electron-phonon interactions. The absence of spectral overlap between the 4f⁶ and 4f⁵5d¹ states leads to inefficient energy transfer from the host matrix to the Sm²⁺ ions.