Preparation,Structure And Properties Of Glass Ceramics For White LED

At present,mainstream commercial white LEDs realize white light emission via the combination of“yellow phosphor+blue light chip”.However,the silicone for packaging is easy to age under high-power light radiation or high temperature,which results in some problems,such as luminous decay,color shift.Therefore,transparent glass ceramic phosphor is proposed to replace the traditional phosphors/polymer color converter,and has become a research hotspot in the field of white LEDs.In this paper,three kinds of glass ceramic phosphors based on ultraviolet or blue light excitation were prepared.Their microstructure and luminescence properties were analyzed by XRD,SEM,TEM,luminescent spectroscopy and other characterization methods.The samples were also coupled with commercial blue light chips to construct white LED devices in order to explore the application in the white LEDs.The research results are listed as follows:?1?A UV-excited transparent glass ceramic based on the CaO-P₂O_5-SiO₂-Al₂O₃-ZrO₂-Eu₂O₃ system was prepared via the overall crystallization method.XRD and TEM results confirmed that 30-50 nm sized?-Ca₃?PO₄?₂ nanocrystals were dispersed evenly in the glass matrix.PLE and PL spectra confirmed the spontaneous reduction of Eu³⁺to Eu²⁺in the precursor glass.Under 362 nm UV excitation,the luminescence color was adjustable by adjusting the doping concentration of Eu₂O₃ and Tb₂O₃.In addition,the energy transferred from Eu²⁺:5d to Tb³⁺:⁵D₄ and Eu³⁺:⁵D₁.?2?A blue-excited glass ceramic based on SiO₂-BaO-Y₂O₃-MgO-Ga₂O₃-ZrO₂-CeF₃ was successfully prepared by high-temperature melting method.XRD and SEM results confirmed the existence of about 3?m sized Y₃Si₂Mg₂GaO₁₂ crystals in the glass matrix.Under the excitation at 465 nm,the sample emitted orange-red light peaked at 602 nm,and the optimal doping concentration of Ce³⁺was 0.4 mol%.When the 1.2 mm thick sample was coupled with a blue chip,the LED device obtained a white light emission with light efficiency of 27.9lm/W,color temperature of 5633 K,and color rendering index of 83.2.?3?A blue-excited transparent afterglow glass ceramic based on the PbO-SiO₂-Al₂O₃-Ga₂O₃-Y₂O₃-H₃BO₃-CeF₃ system was prepared by the frozen sorbet technology.XRD and SEM results confirmed that about 5?m sized Y₃Al_5-xGa_xO₁₂ crystals were dispersed uniformly in the glass matrix.The PL,PLE and afterglow spectra showed that the glass ceramic had the optimized luminescence performance with Ga/Al ratio of 18/12 and Ce³⁺doping concentration of 0.4 mol%,and the afterglow lifetime was 47.32 ms.After co-doping0.4 mol%Sm³⁺,the luminous color and afterglow life of the sample improved significantly.When the 1.2 mm thick sample is coupled with a blue chip,the LED device obtained a white emission with light efficiency of 61.9 lm/W,color temperature of 7546 K,and the color rendering index of 74.6.The flicker index is reduced to 78.6%,and the glass ceramic is expected to be applied in the field of AC-LED.