Rare Earth Activated Sr₃Al₂O₆ Host Phosphors Used For InGaN Chip Base Light Emitting Diodes

The development of white light-emitting diode(WLEDs) induces a newly fast-growing lighting revolution soon after the microelectronics revolution in semiconductor industry.With the advantages of small volume,vibration-resistance,fast response,long lifetime and free pollution,WLEDs as the fourth-generation light source are expected to replace traditional incandescent,fluorescent and High-Intensity gas Discharge lamps.Of presently existing problems,besides luminous efficiency and lifetime of WLED,an important parameterr,color rendering index(CRI),of present InGaN/YAG:Ce WLED pattern is highly needed to improve by developing new non-sulfide base red phosphors,which could be easily excited by blue or ultraviolate blue light in higher efficiency.This research work is focusing on a red and white phosphor with stoichiometric host Sr₃Al₂O₆,including prearation,microstructure and spectrum properties.Innovative results achived in this work include:Ⅰ.Orange phosphor Sr₃Al₂O₆:Eu,Dy³⁺ phosphor excited by blue light have been successfully prepared by spray pyrolysis method from composite sols with nano-scale boehmite as Al resource,reliazing a non-metallic ethylate sol-gel preparation route.Ⅱ.The photoluminescence spectra of as-received Eu²⁺ doped-Sr₃Al₂O₆ phosphors show that the phosphors have the broad excitation band from 400 nm to 500 nm,which match well with the emission wavelength of InGaN-chips,and the emission band peaks at 595 nm, possibly resulting in improvement of color rendering index(CRI) of WLEDs.ⅢFor Sr₃Al₂O₆:Eu,Dy³⁺ phosphor,orange light is ascribed to luminous centre Eu²⁺. The ratio of relative intensities of emission peaks of Eu²⁺ and Eu³⁺ ions in crystal structure of Sr₃Al₂O₆ have been evaluated to reveal that partial replacement of cations by Zn²⁺ and the further introduction of Sr²⁺ vacancies into lattice contribute to reduction of Eu³⁺ to Eu²⁺ inducing enhancement of the luminous efficiency.Ⅳ.By using high-temperature solid-state method,single-host white-light Sr₃Al₂O₆:Dy³⁺ phosphor powders have been obtained.Under the 350 nm excitation the phosphors emit yellow light(578nm) and blue light(484 nm) simultaneously,corresponding to transitions from ⁴F_9/2 to ²H_13/2 and ²H_15/2 within 4t⁹ configuration of Dy³⁺,respectively.The same decay rate of two kind of light are verified to combine the white light uniformly,providing the possibility for fabricating long aftergolow WLED with color stability during decay.Ⅴ.The great difference of characteristic luminous properties of Dy³⁺ with respect to Ca, Sr and Ba in aluminate host has been observed.As for this we interpret linkage form of polyhedronal[AlO₄]in the Ba₃Al₂O₆ host is different from that in the Sr₃Al₂O₆ host.