Light-emission and excited-state dynamics in Tm2+ doped CsCaCl3, CsCaBr3, and CsCaI3

The light-emission and photophysical properties of CsCaCl3:Tm2+ (1.04%), CsCaBr3:Tm2+ (0.48%), and CsCaI3:Tm2+ (0.76%) are presented. We find that Tm2+ is a multiple emitter under 21,834 cm-1 laser excitation at low temperatures in all three compounds. Several distinct types of emission are observed and characterized: sharp and long-lived 4f-4f emission in the infrared (IR) and up to four broad and fast decaying emission bands in the near-IR and visible, originating from the 4f-5d states of Tm2+. The optical spectroscopic properties of the samples are compared, and we find that the measured differences in the relative intensities and the shifts in the position of the emissions can be related to the chemical influence on the absorption and emission properties of Tm2+. Thus, it nicely illustrates the principle of chemical variation on the optical spectroscopic properties. An investigation of the temperature dependence of the luminescence yields important information about the dynamics of the excited states. The interplay and competition between radiative and nonradiative pathways is explained and modeled using a single configurational coordinate approach.