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Fluorescence radiation trapping and nonradiative energy losses from the Nd 3؉ 4 F 3/2 state are reported for two widely used commercial phosphate laser glasses (LHG-8 and LG-770). The effects of hydroxyl-group, transition-metal (Cu, Fe, V, Co, Ni, Cr, Mn, and Pt), and rare-earth (Dy, Pr, Sm, and Ce) impurities on the 4 F 3/2 nonradiative decay rate in these glasses are quantified. Nd concentration quenching effects are reported for doping levels ranging from about 0.5 ؋ 10 20 to 8.0 ؋ 10 20 ions/cm 3 . The results are analyzed using the Förster-Dexter theory for dipolar energy transfer. Quenching rates for transition-metal ions correlate with the magnitude of spectral overlap for Nd emission (donor) and the metal ion absorption (acceptor). The nonradiative decay rates due to hydroxyl groups follow Förster-Dexter theory except at low Nd-doping levels (Շ2 ؋ 10 20 ions/cm 3 ) where the quenching rate becomes independent of the Nd concentration. The data suggest a possible correlation of OH sites with Nd ions in this doping region. The effects of radiation trapping on the fluorescence decay are reported as a function of sample size, shape, and doping level. The results agree well with the theory except for samples with small doping-length products; in these cases, multiple internal reflections from the sample surfaces enhance the trapping effect.

Non-radiative losses due to OH fluorescence quenching of the Nd 3+ 4 F 3/2 state are quantified over a range of OH concentrations from 4 · 10 18 to 4 · 10 20 cm À3 and Nd doping levels from 0.4 to 9 · 10 20 cm À3 in two K 2 O-MgO-Al 2 O 3 -P 2 O 5 metaphosphate glasses having different K/Mg ratios ($1/1 and 2/1). The quenching rate varies linearly with the Nd and OH concentrations as predicted by Forster-Dexter theory. However, in contrast to theory, the OH quenching rate extrapolates to a non-zero value at low Nd 3+ doping levels. It is proposed that at low Nd 3+ concentrations the OH is correlated with Nd sites in the glass. The quenching strength of OH on a per ion basis is weak compared to common transition metal impurities (V, Fe, Co, Ni, Cu and Cr). Nevertheless, OH dominates the Nd quenching in phosphate glass because under most processing conditions OH is present at concentrations 10 2 -10 3 greater than transition metal ion impurities.

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