Terbium-doped calcium germanate (Ca_2GeO)4) as a potential candidate for LED application

摘要

Powder samples of Ca_2GeO_4 doped with 0.5, 1, 2 and 3 at.% Tb~(3+) were prepared via solid-state synthesis technique. The obtaining of pure phase at all dopant concentrations was proved through XRD analyses. In the emission and excitation spectra of the obtained powders, the characteristic peaks of Tb~(3+) ion were observed. The Tb~(3+) excitation spectrum in the range from 300 to 500 nm shows characteristic transitions of Tb~(3+), attributed to the f-f transitions. The strongest peak is located at 379 nm corresponding to the ~7F_6 → ~5D_3 transition. The main emission peak of Tb~(3+) is~5D_4 → ~7F_5 transitions at 545 nm, corresponding to green color. Other transitions are located at 416 (~5D_3 → ~7F)5), 437 (~5D_3 → ~7F_4), 458 (~5D_3 → ~7F_3), 488 (~5D_4 → ~7F_6), 588 (~5D_4 → ~7F_4), 621 (~5D_4 → ~7F_3), 651 (~5D_4 → ~7F_2) and 675 (~5D_4 → ~7F_1) nm. The optimum emission is observed for 2 at.% Tb~(3+) ion concentration. At this concentration dominate also (~5D_4 → ~7F_4) and (~5D_4 → ~7F_3) transitions. CIE coordinates of the samples show different emission colors depending on the active ion concentration. The obtained results confirm that as-prepared terbium-doped materials could be used like green, yellow and reddish phosphors.