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 es tablished that Re to Tm energy transfer occurs with an efficiency that increases with Tm concentration as well as with lower temperature. Co nsistent 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 so me 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 beca me much more marked, with double exponential curves giving decay lifet imes of 5 and 24 mu s for Re, and a rise time of 6 us and decay time o f 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 Gam ma(7)(T-2(2g)) and Tm(H-3(4)) luminescence, plus up-conversion lumines cence from the Tm(D-1(2)) state with only a small Tm((1)G(4)) componen t. 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 wa s now mainly from Tm((1)G(4)), with minor contributions from higher st ates. On irradiation into the Tm(H-3(4)) state with 150 mW of radiatio n of 12 500 cm(-1), up-converted luminescence from Tm((1)G(4)) was aga in seen, but accompanied by luminescence from Mo(T-2(2g)). Energy tran sfer therefore occurs in both directions.