White light emission and laser spectroscopy properties of bismuth-lithium-aluminum-zinc phosphate glasses doped with Dy3+, Eu3+ and co-doped with Dy3+/Eu3+

Spectroscopic investigations of Dy3+, Eu3+ and Dy3+/Eu3+ doped bismuth-lithium-aluminum-zinc phosphate glasses were carried out through analysis of absorption, emission and excitation spectra and decay times. The direct and indirect bandgaps and Urbach energy values were calculated using Tauc's method. Laser parameter values (stimulated emission cross-section, effective bandwidth, gain bandwidth and optical gain) were obtained for the 4F9/2 -> 6H13/2 yellow emission of Dy3+ and 5D0 -> 7F2 red emission of Eu3+ in the singly-doped glasses. The co-doped glass shows emission tonalities neutral white of 4621 K, warm white of 3743 K, orange and reddish-orange, with 39.4 %, 50.8 %, 77.9 % and 90.6 % color purities, under 348, 363, 375 and 393 nm excitations, respectively. Upon 348 nm excitation, europium is sensitized by dysprosium through an energy transfer that could occur from the dysprosium 4F9/2 level to the europium 5D0 and 5D2 levels; in turn, back energy transfer from europium 5D2 level to dysprosium 4F9/2 level could also take place.