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.
Highlights
As a burgeoning technology, solid state lighting is rapidly developing and emerging as a greener candidate to replace the existing technology in the lighting industry
White light-emitting diodes (WLEDs) which made a major breakthrough in solid state lighting technology, are considered as a candidate for superseding conventional incandescent and fluorescent lamps owing to their advantages of long lifetime, low power consumption, high energy efficiency, good reliability, compactness, and environmental-friendly characteristics [1,2,3,4,5]
Compared with the cool white light-emitting diodes (WLEDs), warm WLEDs have lower correlated color temperature (CCT) and are closer to sunlight color, which is beneficial for keeping natural circadian rhythms in humans and offering more visibility
Summary
Solid state lighting is rapidly developing and emerging as a greener candidate to replace the existing technology in the lighting industry. Commercial WLEDs are assembled by combining a chip with powder phosphors, which are usually embedded in epoxy resins This structure is unsuitable for fabricating high power WLEDs. Crystals 2017, 7, 249 due to many drawbacks. The rigid cyclic symmetric structure of single crystals results in high luminous efficiency of active ions. These are helpful for producing high power warm WLEDs to obtain high stability, long lifetime, high luminous efficiency, and excellent color [9,10]. We report the growth of Dy,Ge:BSO single crystals by Bridgman method and demonstrate the capability of generating warm white light under excitation in the ultraviolet (UV) region
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