ENERGY-TRANSFER TO TRACE IMPURITIES IN CS2NAY1-XPRXCL6 - CONSEQUENCESFOR INTERPRETATION OF EMISSION DECAY CURVES

We report tile P-3(0) --> (II4)-I-3, and P-3(0) --> (II4)-I-3 luminesc ence decay curves of Cs2NaY1-xPrxCl6 at 20 K as a function of excitati on wave number in the region of tile transitions to the P-3(0) State n ear 20 602 cm(-1), the P-3(1) State near 21 200 cm(-1) and tile six co mponents of the I-1(6) state distributed over tile region 21164 to abo ut 22000 cm(-1). For x = 0.001 and excitation into the absorption maxi ma, the decay curves are independent of excitation wave number and of tile emission transition monitored, and are exactly exponential. Excit ation at regions of weak absorption between the main absorption bands produces markedly different decay curves characterised by a prominent very fast relaxation at short times and a long exponential tail. The f ast decay is strongly bon-exponential. On increasing tile temperature, this fast process becomes less prominent, and it is not detectable in the 398 K curves. For x greater than or equal to 0.05, tile fast proc ess is not present at any temperature. We propose that this fast proce ss is due to emission from PrCl63- ions perturbed by a nearby water mo lecule.