Thermal window of constant luminescence quantum efficiency of Nd3+-doped phosphate glass

In this work was investigated the luminescence quantum efficiency, η, of Nd-doped phosphate glasses, as a function of temperature (298-438 K), using the normalized lifetime thermal lens technique. This system presents high quantum efficiency at low Nd3+ concentration and at ambient temperature, 98%. In the temperature interval from 298 to 313 K, η, presents a decrease and then becomes constant until 393 K. Above this temperature it decrease again. This thermal quenching process was ascribed to thermally activated low energy phonons, associated to rocking motions of the corner-shared PO4 tetrahedron cluster (order-disorder phase transformation), inducing changing on non-radiative transition that leave to a reduction of luminescence quantum efficiency at 298 and 393 K. From 313 to 393 K occurs a constant window of luminescence quantum efficiency in the PANK+xNd3+ system. This assumption is supported by Differential Scanning Calorimetry and Raman measurements.