Correlation between rare-earth oscillator strengths and rare-earth-valence-band interactions in neodymium-doped YMO4 (M = V, P, As), Y3Al5O12, and LiYF4 matrices

Nd3+:YVO4 is one of the more promising laser hosts for micro and diode-pumped solid-state lasers. At room temperature, Nd3+ ions in this matrix exhibit strong absorption cross sections sixfold higher than in Y3Al5O12 The neodymium oscillator strengths are measured in YMO4- (M=V, P, As), Y3Al5O12, and LiYF4 hosts, and they Increase in the sequence Y3Al5O12<LiYF4<YAsO4<YPO4<YVO4. This paper is an attempt to correlate these variations with covalent interactions between neodymium 4f,5d levels and valence-band levels. The strength of orbital interactions between 4f levels and valence-band states is estimated from the analysis of 3d x-ray photoemission spectra of Nd3+ ions. A two-step model is derived, in which 5d admixture into the 4f levels of the rare earth occurs via the valence-band levels. This model shows that the oscillator strengths increase with the Nd 4f-valence-band interactions.