Synthesis And Properties Of RE-doped Silicate And Silicon-aluminium Oxynitride Phosphors For LED Light Converting

The fabrication and properties of phosphor used for white LED were paid more attentions with the extension of applied field and the development of preparation technology in white LED. In the present study, some phosphors suitable for excitation by near UV light have been synthesized using different methods and raw materials: Firstly, Ba₂SiO₄:Eu²⁺ phosphors co-doped with RE³⁺ (RE³⁺=Nd₂O₃, Yb₂O₃, Pr₆O₁₁, Tb₄O₇, Sm₂O₃) were prepared by conventional solid-state high tempertature reaction in reductive atmosphere. The results showed that these phosphors emit visible light at around 420nm-600nm with a half -width of 57nm under excitation by 300-400nm radioation. The co-doping of Yb, Pr, Tb, and Nd can greatly enhance the fluorescence intensity of Ba₂SiO₄:Eu²⁺phosphors, especially those with variable valance. The excitation and emission peaks of all as-synthesized phosphors are wide bands. The former range from 250 to 400nm, which match the wavelength of near ultraviolet LED chip well and can be used as a potential candidate for the fabrication of white LED. The latter from 450 to 550nm, which are typical 5d-4f transition emission of Eu2+ and display un-symmetry profiles due to the two substitution sites of Ba²⁺ by Eu²⁺ .Second, phosphors containing Sialon were synthesized usingα-Si₃N₄ andα-AlN as materials in reduction atmosphere. The excitation spectra of the phosphors displayed a wide peak at around 350nm-380nm, and the emission spectra were composed of two adjacent peaks at around 520nm and 580nm. The optimum doping concentration of Eu²⁺ was determined to be of 0.03. The luminescence intensity of as-synthesized samples varied with their phase composition which changed with calcinations temperature and holding time. The luminescence intensity increased with the holding time under 1700℃increasing from 0.5 h to 1h and decreased from 1h to 7h. Correspondingly, the phases compositions were found to be the mixture ofβ-Sialon andα-AlN for 0.5h holding time,β-Sialon andα-AlN for 1h,α-AlN for 3 or 7h.Finally, bentonnite was employed to synthesize Eu-doped silicon-aluminium oxynitride phosphor using aluminium heat reduction method. However, onlyβ-Sialon was formed in the as-synthesized samples. The luminescental spectra possessed the characterization of Eu-doped silicate and oxynitride phosphor, displaying a wide excitation peak ranging from 300 to 400nm and a wide emission band at around 450-550 with a tailing to over 600nm. The optimum doping concentration of Eu²⁺ was determined to be of 0.1. A weak excitation spectrum at 460nm was also observed for all the as-synthesized samples, which might be originated from the trace amount of impurity in bentonnite. The co-dopant of Y³⁺ enhanced the fluorescence intensity, but the co-dopant of Yb³⁺ did not. The XRD patterns samples showed that the as-synthesized samples were not composed of pure Sialon phase, which resulted in the wide band emission spectra.