Light-Emission and Excited-State Dynamics in Tm²⁺ Doped CsCaCl₃, CsCaBr₃, and CsCaI₃

Abstract

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.

Upconversion Between 4f–5d Excited States in Tm2+‐Doped CsCaCl3, CsCaBr3, and CsCaI3

“…[e] Excitation at 28 195 cm À1 , from reference [13]. Figure 4 shows the temporal evolution of the 10 K luminescence intensity of emission D in the three samples after 10 ns excitation pulses at 14 450 cm À1 into the ( 3 H 6 ,t 2g ) multiplet.…”

“…From the spectroscopic data of the three samples we conclude that the only band splitting due to symmetry reduction is observable in the 4f-4f transi- www.chemeurj.org tions and is in the order of a few wavenumbers. [13] The data interpretation is therefore done in the octahedral approximation.…”

“…The number of observed Tm 2 + transitions is highly dependent on the host lattice. [10][11][12][13] In all lattices, a sharp and long-lived 4f-4f emission is found in the NIR region. At higher energies, broad and fast decaying emission bands are observed that originate from the 4f-5d states of Tm 2 + .…”

“…The assignment of the excited states and the emission bands has already been discussed for the three compounds in references [13,19]. A brief recapitulation is given here.…”

Characterizations of CsSrCl3:Ce Crystalline Scintillator

“…Auger-free luminescence (AFL), that is, radiative electric transition from the valence band to the outermost core band, in undoped CsMgCl 3 , CsCaCl 3 , and CsSrCl 3 crystals have been intensely studied because of their interesting characteristics such as fast decay times with high thermal stability. (6)(7)(8)(9) The rare-earth-, transition-metal-, and s 2 -ion-doped perovskite chloride crystals have attracted the most attention as the phosphor, (10)(11)(12)(13)(14)(15) magnetic material, (16)(17)(18)(19) and scintillator, (19)(20)(21)(22)(23) and then their crystal growth and characterizations have been reported by some researchers. Among the rare-earth-doped crystals, CsCaCl 3 :Eu and CsSrCl 3 :Eu are proposed to be promising X-ray and gamma-ray scintillators because of their high light yield (~18000 photons/MeV) owing to a 5d-4f allowed transition of Eu…”