Tunable Ho3+ co-doped YOF:Bi3+ emission through cathodoluminescence

Abstract

The tunability of holmium (Ho3+) emission was achieved with bismuth (Bi3+) as a co-dopant in an yttrium oxyfluoride (YOF) host for optoelectronic applications. Cathodoluminescence (CL) studies were investigated under electron beam irradiation (5 keV) for both YOF: x mol % Bi3+ (x = 0.3, 0.4, 0.5, 0.6, 0.8) and YOF: 0.4 mol % Bi3+, x mol % Ho3+ (x = 0.8, 1.4, 2, 3, 4, 5) samples. The samples were synthesized by the pyrolysis technique followed by annealing in ambient air at 900 °C. The structure of all samples exhibited pure rhombohedral YOF. The morphology studies showed small particles that agglomerated into bigger particles after annealing. Ultraviolet CL emission for the single doped Bi3+ samples were attributed to the emission of Bi3+ around 316 nm and the visible emission around 624 nm was attributed to Bi2+. The presence of Bi2+ emission was a result from ionization during electron beam bombardment. The samples co-doped with Bi3+ and Ho3+ ions showed the same emission components of Bi3+ and Bi2+ as well as Ho3+ emission at 540 nm. X-ray photoelectron spectroscopy confirmed the samples’ composition with the presence of Bi2+ as well as the existence of an intermediate Y-O-F layer that must have formed during electron bombardment. The fitted CIE coordinates of the co-doped samples showed that the CL emission can be tuned from green to yellow and to orange.