Multicolor emission in lithium-aluminum-zinc phosphate glasses activated with Dy³⁺, Eu³⁺ and Dy³⁺/Eu³⁺

A spectroscopic analysis of Dy³⁺, Eu³⁺ and Dy³⁺/Eu³⁺ doped lithium-aluminum-zinc phosphate glasses is carried out based on absorption and photoluminescence spectra and decay time measurements. According to the CIE1931 chromaticity coordinates and correlated color temperature (CCT), neutral white and reddish-orange global emissions were observed in the Dy³⁺ and Eu³⁺ singly-doped glasses, respectively, after excitations of Dy³⁺ at 348 nm and Eu³⁺ at 393 nm. A high red color purity of 97.2% is achieved in the Eu³⁺ singly-doped glass excited at 393 nm. Upon Dy³⁺ excitation at 348 nm, the Dy³⁺/Eu³⁺ doped glass showed warm white overall emission, with CCT value of 3629 K. Upon Dy³⁺ and Eu³⁺ co-excitations at 362, 381 and 387 nm, the Dy³⁺/Eu³⁺ doped glass showed reddish-orange overall emissions, with CCT values in the 1620–2385 K range, depending on the excitation wavelength. In the Dy³⁺/Eu³⁺ doped glass excited at 348 nm, the warm white emission was achieved by a non-radiative energy transfer from Dy³⁺ to Eu³⁺ with an efficiency and probability of 0.08 and 89.51 s⁻¹, respectively. The dominant mechanism could be through an electric quadrupole–quadrupole interaction, as it is suggested from the Inokuti-Hirayama model. A back non-radiative energy transfer from Eu³⁺ to Dy³⁺ is also observed, which could also be mediated by an electric quadrupole–quadrupole interaction. The Eu³⁺ to Dy³⁺ energy transfer efficiency and probability being of 0.08 and 30.00 s⁻¹, respectively.