Transition metal sensitizers of thulium luminescence and up-conversion

Absorption spectra of Cs2ZrCl6 doped with Re(IV) and Tm(III) at levels up to 5 mol% were used to confirm and establish the energy levels of these two ions in this host. Steady-state luminescence spectroscopy established that Re to Tm energy transfer occurs with an efficiency that increases with Tm concentration as well as with lower temperature. Consistent with this, the 86 us lifetime of the ReCl62- Gamma(7)(T-2(2g)) state at 90 K was reduced to 48 mu s by the presence of 1% Tm and some early, non-exponential decay became evident. At the same time, the long-lived, 450 mu s, luminescence from the Tm(H-3(4)) state appeared with a 48 mu s risetime. At 5% incorporated Tm, the non-exponentiality of the Re luminescence decay and the rise of the Tm luminescence became much more marked, with double exponential curves giving decay lifetimes of 5 and 24 mu s for Re, and a rise time of 6 us and decay time of 430 mu s for Tm. Over the temperature range 80-298 K, excitation of a 5% Re/5% Tm doped sample with 150 mW 647.1 nm radiated led to Re Gamma(7)(T-2(2g)) and Tm(H-3(4)) luminescence, plus up-conversion luminescence from the Tm(D-1(2)) state with only a small Tm((1)G(4)) component. The first two signals were linear in excitation power while the Tm(D-1(2)) luminescence increased quadratically. The 5% Mo(III)/5% Tm(III) doped Cs2NaYCl6 sample also showed up-conversion when excited at 514 nm into the Mo(III) (T-2(2g)) state. The up-converted luminescence was now mainly from Tm((1)G(4)), with minor contributions from higher states. On irradiation into the Tm(H-3(4)) state with 150 mW of radiation of 12 500 cm(-1), up-converted luminescence from Tm((1)G(4)) was again seen, but accompanied by luminescence from Mo(T-2(2g)). Energy transfer therefore occurs in both directions.