QUANTUM EFFICIENCY AND EXCITED-STATE RELAXATION DYNAMICS IN NEODYMIUM-DOPED PHOSPHATE LASER GLASSES

Radiometrically calibrated spectroscopic techniques employing an integrating-sphere detection system have been used to determine the fluorescence quantum efficiencies for two commercially available Nd3+-doped phosphate laser glasses, LG-750 and LG-760. Quantum efficiencies and fluorescence lifetimes were measured for samples with various neodymium concentrations. It is shown that the effects of concentration quenching are accurately described when both resonant nonradiative excitation hopping (the Burshtein model) and annihilation by cross relaxation are accounted for by Foster-Dexter dipole-dipole energy-transfer theory. The Forster-Dexter critical range for nonradiative excitation hopping was found to be R(DD) = 11 angstrom, while the critical range for cross relaxation was close to R(DA) = 4 angstrom in these glasses. The quantum efficiency at low Nd3+ concentrations was (92 +/- 5)%, implying a nonradiative relaxation rate of 210 +/- 150 s-1 for isolated ions. Improved values for the radiative lifetimes and the stimulated emission cross sections for these glasses were also deduced from the measurements.