Neodymium fluorescence quenching by hydroxyl groups in phosphate laser glasses

Non-radiative losses due to OH fluorescence quenching of the Nd3+ 4F3/2 state are quantified over a range of OH concentrations from 4 × 1018 to 4 × 1020 cm−3 and Nd doping levels from 0.4 to 9 × 1020 cm−3 in two K2O–MgO–Al2O3–P2O5 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 Nd3+ doping levels. It is proposed that at low Nd3+ 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 102–103 greater than transition metal ion impurities.