Spectroscopic properties, Judd Ofelt analysis of U and Eu activated Li2O-ZnO-SrO-B2O3-P2O5 borophosphate glasses for solid-state lighting applications

Abstract

Uranium and europium doped borophosphate glasses with the base composition of (Li2O)(ZnO)0.5(SrO)0.4(B2O3)2.55(P2O5)0.5 were synthesized by melt -quenching. The X-ray diffraction profile affirmed that all the synthesized samples were devoid of crystallinity and amorphous in structure. The absence of precipitations/grains in the scanning electron micrographs further validated the amorphous character and compositional homogeneity of the prepared glass. The FTIR spectra revealed several prominent vibrational bands in 713–1568 cm−1 range and were assigned to the corresponding B-O-B and P-O-P and B-O-P bonding. The thermal characteristics of the synthesised glass samples were investigated using differential thermal analysis experiments. The broad photoluminescence (PL) spectra observed for the uranium doped glass with emission maxima at 523 nm resembles the hexavalent U(VI) emission in a disordered amorphous environment. The emission profile of the Eu doped glass displayed several characteristics peaks due to 5D0 → 7FJ transitions. The phonon energy of the base glass was found to be 1005 cm−1. The Judd-Ofelt analysis showed that for all the doped glass, the JO intensity parameter Ω4 was always greater than Ω2 indicating that Eu3+ ions are primarily arranged in a centrosymmetric environment in the studied host. Radiative properties of 5D0 → 7FJ=1-4 transitions of the Eu3+ such as branching ratios, emission cross-section, and transition probabilities were computed. Energy transfer pathways of UO22+ → Eu3+ in the codoped borophosphate glass were described. The CIE chromaticity and PL results suggest that the intense red emission of Eu doped glasses could be useful for phosphor applications.