Site-selectivity of up-conversion processes in Ti : Er : LiNbO3 waveguides

Starting out from previous investigations on the population dynamics of Er3 + ions in Ti,LiNbO waveguides and predictions for possible laser operation at 550 nm and 3 mu m we studied the dependence of the up-conversion efficie ncy on the different lattice environments ("sites") encountered by the Er3 ion. For that purpose we developed and employed a combined excitation emis sion spectroscopy for waveguides at low temperatures. Comparing the result for the green luminescence (550 nm) obtained under direct excitation at 450 nm with that detected for two-step excitation (980 nm) we find, like for b ulk material, several sites in the waveguides which participate with differ ent efficiencies and mechanisms in the up-conversion process. On the basis of commonly accepted microscopic models for the sites, we discuss these exc itation processes and the consequence of the found site distribution for th e possibility to achieve population inversion. (C) 1999 Elsevier Science B. V. All rights reserved.