Warm-white, reddish-orange and orange light generation from lithium-aluminum-zinc phosphate glass tri-doped with Sm3+, Tb3+and Eu3+

Abstract

Spectroscopic evaluation of Sm3+/Tb3+/Eu3+ doped lithium-aluminum-zinc phosphate glass (LAZSTE), based on photoluminescence spectra and emission decay profiles, is particularly focused on W-LED technology. Tauc's method is employed to find direct and indirect allowed band gap and Urbach energy values. The Judd-Ofelt parameters were evaluated from measured oscillator strengths and subsequently used to estimate various radiative properties for the prominent fluorescent transitions (4G5/2 → 6H5/2, 4G5/2 → 6H7/2 and 4G5/2 → 6H9/2) of Sm3+ ions. The LAZSTE glass excited at 346, 377 and 408 nm, displays warm-white light emission of 2497 K, orange light emission of 1949 K and reddish-orange light emission of 1667 K respectively, according to (0.4753, 0.4121), (0.5306, 0.4130) and (0.6077, 0.3767) CIE1931 chromaticity coordinates, respectively. The Tb3+ and Sm3+ emission decay shortening in presence of Sm3+ and Eu3+, and Eu3+, respectively, suggests that non-radiative energy transfer processes could take place from Tb3+ to Sm3+ and/or Eu3+, and from Sm3+ to Eu3+. The analysis of the Sm3+ and Tb3+ emission decays, performed with the Inokuti-Hirayama model, suggests that all these energy transfer processes are predominantly mediated through an electric dipole-dipole interaction, inside Sm3+-Tb3+-Eu3+ clusters.