Phase And Valence State Of YAG Phosphors For Light Emitting Diode And Optical Properties

Thermal stability of YAG:Ce commercial phosphor need to be increased especially forhigh-power LEDs. Resin or silicon material in white LED device is generally apt to degradeat high temperature, leading to shortening of lifespan and lowering luminance efficiency ofdevice. Preparing YAG:Ce phosphor need reductive atmosphere and attain YAG pure phase.To solve the problem above, we investigated YAG:Ce ceramic bulk phosphor in the airatmosphere. The problems in valence state of activator and purity of host phase for this kindof ceramic are focused on by introducing Si-O bond to host. The main achievements aremade that includes:1. The self-reduction phenomena from Ce⁴⁺to Ce³⁺in YAG:Ce samples was observed tobe featured in a typical 5dâ†'4f yellow-green transition of Ce³⁺ion upon firing in air, theaddition of SiO₂promopts further reduction phenomenon. Upon blue light excitation, theemission peak is located at 534 nm. XRD measurement confirms that YAG pure ceramics areformed.2. Theoretic analysis shows luminance center of Ce³⁺ion concentration that is linked withthe charge compensation owing to SiO₂addition. Addition of 7% SiO₂leads to promotion ofself-reduction from Ce⁴⁺to Ce³⁺ion. Luminance intensity was increased for the YAG:Cesamples that were doped SiO₂in 7.0 wt.% than those with un-doped samples.3. Structure analysis shows that the addition of SiO₂results in blue shift of emissionspectrum. To achieve red shift of emission spectrum, addition of LiF was tested and observeda narrowing of 5d and 4f energy level and a red shift of dominant wavelength, leadsing toimprovement of color rendering and descending of corrected color temperature （CCT）.4. Model of remote phosphors for packaging white LED device that adopts YAG:Ceceramics was sintered via SiO₂addition. Average size of YAG ceramic is approximately twomicro meters. The broad absorption band of Ce³⁺is from 410 to 510 nm. The exciting peakand the emission peak are located at 468 nm and 534 nm, respectively.The results of the mentioned above in the valence stability regulation of Ce and newtechnique of pure phase formation have a reference value. The remote phosphors forpackaging device have a potential application.