Effect of U on the photoluminescence of Pr and structural properties of U/Pr doped and co-doped Li2O–ZnO–SrO borophosphate glass

Abstract

U/Pr doped and co-doped Li2O–ZnO–SrO borophosphate glasses were prepared using the melt quenching method. XRD, SEM-EDX, and FTIR investigations were carried out to ascertain the structural properties, morphological features and homogeneity of elemental distribution in the synthesised glass phosphors. Differential thermal analysis was used to examine the thermo-physical properties. It was observed that uranium doping improved the thermal stability and rigidity of the synthesised glass host. Intense photoluminescence (PL) emissions were observed both from uranium and praseodymium in the U/Pr doped glass. Uranium showed a broad emission spectrum with peak a maximum at 526 nm and resembles the typical emission pattern of hexavalent uranyl species (UO22+) in the amorphous environment. UO22+ emission increased linearly until the onset of concentration quenching at 1.0 mol%. Similarly, praseodymium doped glasses exhibited intense red emission from overlapped 3P0→ 3H6 and 1D2 →3H4 transitions, and centred at around 609 nm. At 0.2 mol%, the Pr emission intensity was highest, concentration quenching was prevalent beyond it. The emission decay of both uranium and praseodymium followed the bi-exponential decay model and the lifetime values decreased with increasing the dopant concentration in singly doped as well as co-doped samples. The Inokuti-Hirayama model was employed for the fitting of decay profiles to explicate the nature of non-radiative interaction of excited states. The donor-acceptor coupling parameters (Cda) were determined for U–U, Pr–Pr, and U–Pr interaction. Appreciable U–Pr energy transfer via dipole-dipole interaction was observed with Cda = 4.79 × 10−40 cm6s−1. Emission of both Pr and U get suppressed in the co-doped glass samples possibly due to the concomitant U–Pr redox interactions. The CIE color coordinates and color purity suggested that U/Pr doped Li2O–ZnO–SrO borophosphate glass can be used for solid-state lighting applications.