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.