Energy transfer processes and the green fluorescence in heavily doped Er3+:: fluoride glasses

The thermalised (S-4(3/2) + H-2(11/2)) level plays a significant role in the overall population dynamics of Er3+ in fluoride glasses. A detailed study of the fluorescence waveforms from this level was conducted in Er3+-doped ZBAN glasses over a wide range of doping concentrations (0.2-18 mol%). Direct (520 nm) and up-conversion (800 nm) pumping were used in this study. Rate-equation analysis was used to identify and characterise the energy-transfer processes responsible for the observed fluorescence behaviour. Three-ion processes were found to be very important in the overall population dynamics, even at low doping concentrations. With direct pumping the decay waveforms remained exponential for high Er3+ concentrations (e.g. 18 mol%). Two-ion and three-ion processes, that involve the ground state, were found to decrease the lifetime of the level from about 550 mus (0.2 mol%) to about 3 mus (18 mol%). With 800-nm pumping, the level received its initial population by multiphonon decay from the H-2(9/2) level which is populated by excited-state absorption of the pump. The decay of the (S-4(3/2) + H-2(11/2)) level was found to be comprised of two components. The initial component was very similar to that observed with direct pumping and was again influenced by the above-mentioned multi-ion processes. The second component was the result of multi-ion processes involving the I-4(11/2) level that transfer population from this level to the (S-4(3/2) + H-2(11/2)) level. (C) 2003 Elsevier Science B.V. All rights reserved.