Structural and spectroscopic properties of phosphate–tungsten glasses doped with Nd3+ and Tb3+

Glasses of composition 90NaPO3-10WO3-xNd2O3, (0 ≤ x ≤ 1.7 mol%) and 90NaPO3-10WO3-yTbF3, (0 ≤ y ≤ 5.0 mol%) have been prepared and characterized. 31P and 23Na magic-angle spinning (MAS) NMR and 23Na{31P} rotational echo double resonance results are consistent with previously published data, indicating the presence of Q(2) and Q(1)1 W units. In addition, linear dependences of 31P MAS-NMR linewidths and spin-lattice relaxation rates and the electron spin-spin relaxation behavior (in the case of Nd2O3 doping) are consistent with a random dopant distribution, For Nd2O3- doped glass samples, absorption spectra in the visible and infrared regions were collected and analysed, and photoluminescence excitation and emission spectra were obtained under 575 nm excitation. Using the Judd-Ofelt formalism, the Ω2, Ω4 and Ω6 parameters were determined and by using them, the radiative lifetime (τr) were calculated for the 4F3/2 excited state. The fluorescence quantum efficiency value for this level (QE = τf/τr) of 13% was determined for glass with x = 1.0. The photophysical properties of Tb- doped glasses were also studied and upon UV excitation (372 nm) the glasses show emissions in the green (540 nm, 5D4 → 7F5 transition) and blue (434 nm, 5D3 → 7F4). The relative luminescence intensity ratio 5D3 → 7F5/5D4 → 7F5 is higher for lower Tb3+ content (0.5 Tb glass sample), because for higher Tb3+ contents, a cross-relaxation energy transfer process takes place favoring the green emission.