Spectroscopic evidence of inhomogeneous distribution of Nd3+ in YVO4, YPO4 and YAsO4 crystals

Nd3+:YVO4 is one of the most interesting laser hosts for micro and diode-pumped solid state lasers. We have studied magnetic and optical properties of Nd3+ in three zircon type crystals YMO4 (M = V, As, P). In particular, Nd3+ ions exhibit in the three hosts a multisite character observed in the absorption and emission spectra. However, the emission and its dynamics are strongly dependant on the reabsorption mechanisms. In Nd:YVO4, single crystals containing 7 +/- 1 x 10(18) Nd3+ ions/cm(3), the lifetime is 95 +/- 2 mu s in good agreement with the calculated radiative lifetime. Electron Paramagnetic Resonance (EPR) measurements are performed to identify the nature of the different substitution sites for Nd3+ ions. Nd3+ ions are found to be inhomogeneously distributed in tetragonal D-2d symmetry sites, in isolated ions, shallow clusters and pairs. Proportions of the different local environments depend on the total neodymium concentration. For instance, 15% of the Nd3+ ions are gathered in Nd3+-Nd3+ pairs for 7.2 +/- 0.2 x 10(19) Nd3+ ions/cm3. (C) 2000 Elsevier Science B.V.. All rights reserved.