Anomalous fluorescence quenching and spectral diffusion in neodymium doped lanthanum pentaphosphate

An investigation of donor-donor and donor-acceptor spectral dynamics in La/sub 1-x/P5O14:Nd/sub x/3+ is presented. The fluorescence from the 4F/sub 3/2/(1) state in this high-gain laser material is characterized by an anomalous exponential decay and a linearly dependent concentration quenching rate between 4 K and 300 K. The technique of time resolved fluorescence line narrowing is employed with resonant excitation of the 4F/sub 3/2/(1) state, provided by a narrow-band, pulsed near-IR laser system, to study the Nd3+-Nd3+ interactions within this space. Excitation spectra of the 4F/sub 3/2/(1) state in x = 0.2, 0.75, and 1.0 samples indicate single, inhomogeneously broadened levels. The fluorescence spectra and lifetime measurements at low temperature (approx. =5 K) show the presence of a non-uniform distribution of Nd3+ ions across the inhomogeneous line. Below approximately 20 K no spectral diffusion is observed for all three concentrations, indicating an absence of donor-donor transfer at these temperatures. Spectral diffusion is observed for x = 0.75 at approx. =20 K, which establishes the presence of phonon-assisted energy transfer in this compound. The temperature dependence of the spectral diffusion for x = 0.2 is measured between 17 and 24 K. The low temperature results and the spectral diffusion measurements are described in a consistent manner by existing, phonon assisted spectral energy transfer theories. There is no evidence from this investigation for coherent ion-ion interactions in La/sub 1-x/P5O14:Nd/sub x/3+ in the studied temperature region