Mixed ionic-electronic effect on up-conversion in Er3+/V4+ co-doped Na2O-CaO-B2O3 glasses with enhanced red emission

Abstract

Optical absorption and emission properties of 20Na2O–20CaO–(59 – x)B2O3–xV2O5–1Er2O3 (x = 0 – 2.5 mol%) (Series A) and 20Na2O–20CaO–(58.5 – y)B2O3–1.5V2O5–yEr2O3 (y = 0 – 3.0 mol%) (Series B) glass systems were examined to elucidate the effect of Er2O3 co–doping with V2O5 in the mixed ionic–electronic (MIE) glasses. The absorption spectra of both glass series exhibited 10 significant bands, which corresponded to the f–f transition of Er3+ ions with an additional weak absorption band attributed to V4+ energy transition. The up–conversion PL spectra for the glasses under 779 nm excitation displayed 3 emissions bands centered at 518, 556 and 647 nm due to the emission from the energy levels of Er3+. The enhanced emission at 647 nm (red region) that corresponded to the 4F9/2 → 4I15/2 of the Er3+ transition for all glasses was suggested due to energy transfer from V4+ to Er3+ ions. For Series A, the variation of oscillator strength (fexp) and Judd–Ofelt parameters (Ω2,4,6) showed almost similar trend, which exhibit a maximum at x = 0.5 mol% V2O5. PL intensity was highest for sample x = 0.5 mol% but abruptly drops to the minimum at x = 1.5 mol%. The decrease in PL was possibly influenced by the MIE effect. Meanwhile, for Series B glasses, general decrease was observed in fexp and Judd–Ofelt parameters except for Ω6 upon Er2O3 addition. The PL intensity increased and reached a maximum at y = 2.0 mol% before subsequently decreased with further addition of Er2O3 (y = 3.0 mol%) due to concentration quenching.