Concentration and temperature dependent luminescence properties of the SrI2-TmI2 system

M. P. Plokker, W. Hoogsteen, R. D. Abellon, K. W. Krämer, E. van der Kolk

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Abstract

The concentration dependent luminescence of the SrI2-TmI2 system was investigated. For Tm2+ concentrations up to 5 mol %, the quantum efficiency (QE) of the 2F5/22F7/2 emission exhibits a constant value above 50%. The QE drops for higher Tm2+ concentrations, partly due to concentration quenching, as evidenced by a decreasing luminescence lifetime of the 2F5/22F7/2 emission, and partly due to the formation of a second crystal phase with CdCl2 structure, in which the 2F5/22F7/2 emission is quenched. The temperature and time dependent relaxation dynamics were studied to identify the origin of the limited QE for Tm2+-doping levels below 5 mol %. An anti-correlation between the 5d-4f (3H6,t2g)S=3/22F7/2 and 4f-4f 2F5/22F7/2 emission intensities was found and rationalised by non-radiative, thermally stimulated, inter-configurational 5d-4f relaxation to the emitting 2F5/2 level of Tm2+. Both, the rise time of the 4f-4f and the decay time of the 5d-4f emission become shorter with increasing temperature. We suggest a similar non-radiative relaxation from the 5d level towards the 2F7/2 ground state to limit the QE below unity. This route becomes more efficient when the 5d (3H6,t2g)S=3/2 state moves closer to the 4f 2F5/2 and 2F7/2 states, which is the case for the CdCl2 phase with a QE close to zero.

Original languageEnglish
Article number117327
Number of pages8
JournalJournal of Luminescence
Volume225
DOIs
Publication statusPublished - 2020

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