Co-emission and energy transfer of Sm³⁺ and/or Eu³⁺ activated zinc-germanate- tellurite glass as a potential tunable orange to reddish-orange phosphor

Sm³⁺/Eu³⁺ single doped and co-doped zinc-germanate-tellurite glasses were prepared by the glass melting method. Raman and optical spectroscopic properties of Sm³⁺, Eu³⁺ and Sm³⁺/Eu³⁺ doped TeO₂-GeO₂-ZnO glasses have been characterized through optical absorption and pulsed/steady fluorescence. Excitation and emission spectra measurements indicated that the energy transfer process Sm → Eu is active in the samples. The concentration of europium ions was varied to provide red emission for possible control over the chromaticity tuning in the red-orange region. Upon 344 nm excitation, the color of the global emission can be adjusted from orange of 2038 K to reddish-orange of 1683 K by increasing the Eu³⁺ content from 1 up to 2% mol, and co-doped with 0.5% mol Sm³⁺. Reddish-orange color purity very close to 100% is attained when the phosphors are excited at 406 nm. The time shortening of Sm³⁺ emission decay in the presence of Eu³⁺ was attributed to a Sm³⁺ → Eu³⁺ non-radiative energy transfer process. From fitting the Sm³⁺ emission decay profile with the Inokuti-Hirayama model, it was inferred that the energy transfer process could be dominated by an electric dipole-dipole interaction.