Optimization of luminescence and quantum yield via synergistic energy transfer in Gd3+/Eu3+activated phosphate glasses for red LEDs display technology

Abstract

Phosphate glasses with composition 22K<inf>2</inf>O-9Al<inf>2</inf>O<inf>3</inf>-1ZrO<inf>2</inf>-(63-X)P<inf>2</inf>O<inf>5</inf>-5Gd<inf>2</inf>O<inf>3</inf>-XEu<inf>2</inf>O<inf>3,</inf> herein X = 0.0, 0.1, 0.3, 0.5, 1.0, 2.0 mol%, were synthesized by the melt-quenching method. All specimens were investigated for optical, photoluminescence, and lasing properties through various characterization techniques, including optical absorption, photoluminescence excitation and emission spectra, Judd-Ofelt (J-O) analysis, decay time, and quantum yield measurements. The UV–Vis–NIR absorption spectra revealed eight peaks, with a hypersensitive transition located at⁷F<inf>0</inf> →⁵L<inf>6</inf>. The oscillator strengths calculated from the transitions of the absorption spectra showed maximum values for the hypersensitive transition, while the intensity parameters followed the trend Ω<inf>4</inf> > Ω<inf>2</inf> > Ω<inf>6,</inf> quantifying covalency in Eu³⁺–ligand bonds. The photoluminescence spectra recorded at 312 nm corresponded to the⁶P<inf>7/2</inf> → ⁸S<inf>7/2</inf> transition for Gd³⁺ions, and 613 nm corresponded to the⁵D<inf>0</inf>→⁷F<inf>2</inf> transition of Eu³⁺ions. Radiative transition probability (A<inf>R</inf>) of 491.53 s⁻¹, stimulated emission cross (σ<inf>e</inf>) of 20.15 × 10⁻²² cm², branching ratios (β<inf>R</inf>, β<inf>cal</inf>) of 0.7100, 0.4695, and calculated lifetime (τ<inf>R</inf>) of 0.955 ms and experimental lifetime (τ<inf>R</inf>) of 0.762 ms were determined as the optimal radiative parameters for 613 nm emission. Results from the RL spectra were akin to those obtained from the PL emission spectra. The overlap between excitation and emission spectra, as well as the reduction in donor (Gd³⁺) lifetime, confirmed the energy transfer process. The CIE chromaticity coordinates were spotted in the red-orange region. Calculations of the quantum yield showed an increase up to a maximum of 64.69 % at 2.0 mol% Eu<inf>2</inf>O<inf>3</inf>. All results indicate that the synthesized glass samples are promising candidates for solid-state lighting applications.