Mixed former effect in barium borophosphate glasses on the red (Eu3+)-blue (Eu2+) emission for LEDs

Abstract

The synergistic mixing of P2O5 and B2O3 glass formers at a constant concentration of BaO as a glass modifier plays a vital role in generating a single-phase phosphor doped with Eu2O3 for white light-emitting diodes (WLEDs). Herein, a glass system of nominal composition xP2O5∙(50-x)B2O3∙49.5BaO∙0.5Eu2O3 (0 ≤ x ≤ 50 mol%) was prepared using a melt-quenching technique under normal atmospheric conditions. While the XRD patterns demonstrated the amorphous nature, the SEM micrographs proved the formation of cluster structures. Structural characterization using ATR-FTIR spectroscopy revealed the presence of main vibrational structural units associated with borate and phosphate glass formers, including BO3, BO4−, P=O, PO2−, and PO32−. The IR spectra at x = 0 and 50 mol% exhibit characteristic metaborate and metaphosphate absorption peaks, respectively. In contrast, the mixing of both B2O3 and P2O5 at equal concentrations (x = 25 mol%) has resulted in the absence of absorption peaks assigned to the BO3 and P=O units, thus indicating the mixed structural effect. This is assigned to the formation of B-O-P bonds, with the BO4−, PO2−, and PO32− as the main structural units. These structural changes affect the reduction process of Eu3+ to Eu2+, as demonstrated by the corresponding photoluminescence spectra and observed by the cathodoluminescence micrographs. Photoluminescence studies showed tunable emission from red (Eu3+) to white light (Eu2+ and Eu3+) under UV excitation, with the P2O5 content rising from 0 to 50 mol% due to the growing Eu2+ population formed by the reduction of Eu3+. The optical basicity was observed to decrease with the P2O5 content, favouring the reduction process. The demonstrated tunable single-host white phosphor makes this an attractive system for energy-efficient WLED applications.