Crystal Growth and Luminescence Properties of Dy3+ and Ge4+ Co-Doped Bi4Si3O12 Single Crystals for High Power Warm White LED

Phi 1 inch Dy3+ and Ge4+ co-doped bismuth silicate (Bi4Si3O12, BSO) single crystals with the length of 80-100 mm were successfully grown by Bridgman method. They are transparent, free of cracks and inclusions. The white residual at the top parts of BSO crystals disappears with co-doping 1 mol% Dy3+ and more than 3 mol% Ge4+. The FWHM values of X-ray rocking curves shows 1% Dy,3% Ge:BSO crystal possesses high crystallization quality. The intrinsic emission peak of BSO and the characteristic emission peaks of Dy3+ ions are weakened with increasing the doping concentration of Ge4+. 1 mol% Dy3+ and 3 mol% Ge4+ are the optimal concentrations due to high crystallization quality and moderate emission intensity. The CIE coordinates and CCT values shift towards warmer white light region with increased Ge4+ co-doping. The CCT values are close to the ideal value of 3000 K for warm white light when 1% Dy, 3% Ge: BSO crystal is excited by various UV light. Increasing the temperature from 298 K to 573 K leads the luminescence lifetime to decrease from 659 mu s to 645 mu s. More than 95% and 80% photoluminescence intensity at room temperature is still retained at 423 K and 573 K respectively. Dy, Ge: BSO crystals are potential candidates for fabricating high power warm WLEDs.