Multicolor green to orange-red emission of Tb³⁺ and Eu³⁺-codoped tellurite glasses: Eu³⁺ concentration and Tb³⁺ → Eu³⁺ energy transfer

A series of the TeO₂–GeO₂–ZnO glass system was single and double doped with different Tb³⁺/Eu³⁺ ratios. Their luminescent and colorimetric properties were analyzed for possible use as phosphor materials in lighting devices. The characterization by X-ray diffraction and Raman spectroscopy verified the glassy nature of the fabricated samples. The luminescent properties of the doped glasses were analyzed by means of steady-state fluorescence and time-resolved spectroscopy. The Tb³⁺ excitation bands observed in the codoped samples while monitoring the 700 nm emission of Eu³⁺, as well as the shortening of Tb³⁺ lifetime in presence of europium indicated a Tb³⁺ → Eu³⁺ energy transfer, which main interaction type is electric dipole–dipole, according to Inokuti–Hirayama model. The Eu³⁺ → Tb³⁺ energy transfer also occurs in the samples but with lower efficiency. The CIE1931 chromaticity coordinates, upon different excitation wavelengths, show a multicolor tunning from green to orange-red due to the lanthanide concentration ratio and the Tb³⁺ → Eu³⁺ energy transfer process.