Absolute quantum efficiency of the luminescence emitted from neodymium-activated glasses

The absolute quantum efficiencies of the luminescence q were determined for several neodymium-activated glasses. The values of q were measured by two methods: 1) direct determination of q in two identical integrating-sphere systems with different radiation detectors; 2) spectroscopic determination of the radiative lifetime τ₀ of the metastable level ⁴F_3/2 and calculation of q from a comparison of τ₀ with the average lifetime found experimentally. The values of q found by these two methods were in good agreement for glasses characterized by the exponential decay law but they did not agree for glasses with a complex decay law. The results indicated that the radiative probabilities deduced from the absorption spectrum could not always be used in calculations of the quantum efficiency when these probabilities varied from one situation to another. The value of q was found to be independent of the exciting-light wavelength. The values of q for silicate and phosphate glasses containing 2×10²⁰ cm^–3 neodymium ions were within the range 0.74–0.81. It was concluded that the values of q equal to unity could be obtained for dehydrated silicate and phosphate glasses with low Nd³⁺ concentrations.