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

Glasses of composition 90NaPO(3)-10WO(3)-xNd(2)O(3), (0 <= x <= 1.7 mol%) and 90NaPO(3)-10WO(3)-yTbF(3), (0 <= y <= 5.0 mol%) have been prepared and characterized. P-31 and Na-23 magic-angle spinning (MAS) NMR and Na-23{P-31} rotational echo double resonance results are consistent with previously published data, indicating the presence of Q((2)) and Q(1 W)((1)) units. In addition, linear dependences of P-31 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 Omega(2), Omega(4) and Omega(6) parameters were determined and by using them, the radiative lifetime (tau(r)) were calculated for the F-4(3/2) excited state. The fluorescence quantum efficiency value for this level (QE = tau(f)/tau(r)) 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, D-5(4) -> F-7(5) transition) and blue (434 nm, D-5(3) -> F-7(4)). The relative luminescence intensity ratio D-5(3) -> F-7(5)/D-5(4) -> F-7(5) 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.