Crystal growth and luminescence properties of Dy3+ and Ge4+ Co-doped Bi4Si3O12 single crystals for high power warm white LED

Abstract

Φ1 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 µs to 645 µs. 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.