Terbium-doped calcium germanate (Ca 2 GeO 4 ) as a potential candidate for LED application

Powder samples of Ca2GeO4 doped with 0.5, 1, 2 and 3 at.% Tb3+ 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 Tb3+ ion were observed. The Tb3+ excitation spectrum in the range from 300 to 500 nm shows characteristic transitions of Tb3+, attributed to the f–f transitions. The strongest peak is located at 379 nm corresponding to the 7F6 → 5D3 transition. The main emission peak of Tb3+ is 5D4 → 7F5 transitions at 545 nm, corresponding to green color. Other transitions are located at 416 (5D3 → 7F5), 437 (5D3 → 7F4), 458 (5D3 → 7F3), 488 (5D4 → 7F6), 588 (5D4 → 7F4), 621 (5D4 → 7F3), 651 (5D4 → 7F2) and 675 (5D4 → 7F1) nm. The optimum emission is observed for 2 at.% Tb3+ ion concentration. At this concentration dominate also (5D4 → 7F4) and (5D4 → 7F3) 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.