Sm3+ doped novel Sr2Ga2GeO7 based high thermal stability red-emitting phosphors for efficient WLED

Abstract A series of Sm3+ doped phosphor Sr2Ga2GeO7:xSm3+ (0 = x ≤ 0.05) were synthesized for the first time to obtain red emitting component for efficient WLED device with excellent electroluminescence (EL) performance. The X-ray diffraction (XRD) analysis revealed that these powders crystalized in a tetragonal with a space group of P-421m (113) and the Sm3+ occupied the positions Sr2+ ions in the lattice of Sr2Ga2GeO7. The germanate material Sr2Ga2GeO7 possess a broad optical energy bandgap (Eg) of 5.03 eV, which was beneficial for the charge transfer of Sm3+ to the matrix. The photoluminous (PL) properties proved that these red emitting phosphors Sr2Ga2GeO7:xSm3+ (0 = x ≤ 0.05) exhibited two emission peaks at about 563 nm and 602 nm, which originated from the 4G5/2 → 6H5/2 and 4G5/2 → 6H7/2 transitions of Sm3+ ions under 404 nm excitation. Interestingly, when the contents of Sm3+ reached 2% mol, sample Sr2Ga2GeO7:0.02Sm3+ possessed a relatively best PL characterize with the CIE coordinates of (0.5386, 0.4563). Based on its good PL emission stability and decay lifetime, sample Sr2Ga2GeO7:0.02Sm3+ showed an excellent thermal stability with the PL emission intensity only reduced by 15.02% relative to its initial PL emission intensity when measured at 473 K. As a result, the WLED device based on phosphor Sr2Ga2GeO7:0.02Sm3+ presented a splendid EL performance, with a low correlated color temperature (CCT) of 4252 K, a high color rendering index (Ra) of 90.6 and the CIE coordinates of (0.3701, 0.3707).