Optical spectra and excited state relaxation dynamics of Sm2+ ions in SrCl2, SrBr2 and SrI2 crystals

Abstract

Samarium(2+) doped single crystals of SrCl2, SrBr2 and SrI2 with a nominal samarium concentration of 0.12, 0.16 and 0.13at%, respectively, were grown by the Bridgman method.XRD examination revealed that obtained samples are single phase and their structures are consistent with those intentional. Based on preliminary spectroscopic measurement it was ascertained that Sm2+ ions are incorporated without traces of Sm3+ contamination. High resolution absorption, luminescence and excitation spectra as well as luminescence decay curves were measured as a function of temperature in the 4.2–300K region. It was found that structural peculiarities of the host crystals affect strongly spectroscopic features of incorporated Sm2+ ions. At room temperature all systems under study show a broad-band luminescence related to the parity allowed inter-configurational 4f55d1 – 4f6 transitions of Sm2+. At 5K a broad band luminescence vanishes in SrCl2:Sm2+ and a resulting luminescence spectrum shows a rich fine structure consisting of narrow lines that we attribute to magnetic dipole transitions within the 4f6 configuration of Sm2+ ions located in centro-symmetric sites and/or their vibrational side bands. Based on an analysis of luminescence decay curves we attribute numerous narrow lines that appear in luminescence spectra of SrBr2:Sm2+ recorded below 25K to the 5D0 – 7FJ (J = 0–4) intra-configurational transitions of Sm2+ ions located in sites with C4 and C1 symmetry. A long-lived luminescence related to intra-configurational transitions was not observed in SrI2:Sm2+ even at 4.2K.