The Study On Preparation And Characterization Of Ce³⁺ And Cr³⁺ Codoped YAG Phosphor For White LEDs Application

The energy-saving and environmentally friendly way of development have reached a consensus in the worldwide, the concepts of energy-saving and environmental friendness have been intensively recognized in the worldwide. the development of the field of lighting also follow this philosophy. Compared to traditional lighting, the white LED lighting has many advantages and therefore be considered as the next generation of lighting. Currently, combining Yellow phosphor with blue LED chips to obtain white light LED(named as phosphor converted LEDs, or pc-LEDs) is a mainstream technology, which can achieve a more efficient white light emission. However, since the white light is formed by a mixture of blue and yellow light, the emission spectrum lack of red component, the color rendering index(CRI) is relatively lower. In pc-LEDs, the phosphor technology palys a essential part for the development of white LEDs. The focus of this work is preparation and characterization of co-doped Ce3+, Cr3+: YAG phosphor. With this newly-developed phosphor, the spectrum with plenty red emission can be expected and the CRI of white LEDs can be improved greately thereby.In this paper, three synthetic methods i.e. Solid-State Reaction method, Co-Precipitation method and Sol-Gel method have been carried out in the preparation of Ce3+, Cr3+ co-doped YAG(Y3-yCey Al5-x Crx O12) phosphor with y=0.06, x=0~0.03. referred to standard card of YAG, the XRD measurement prove the good crystallnility of prepared phosphor. With scherrer theory, the grain size is estimated to be 50 nm. The intensive red emission at lmax=718 nm have beed observed due to transition of Cr3+ ion in YAG. The excitation spectrum measurement shows the evidence of energy transfer from 2D3/2 state of Cr3+ to 4T of Cr3+ ion. The measurement also reveals that there is no observable concentration quenching occurred with the increasing concentration of Cr3+ dopent in obtained phosphor.The SEM pictures reveal that the samples prepared in co-precipitaion way show better morphology and less agglomeration than others. The light intensity and chromaticity measurement on those white LEDs coated with prepared phosphor have been performed and discussed. The white LEDs with YAG: Ce3+, Cr3+ phosphor have the CCT(correlated color temperature) of 5500 K and a CRI of 82.6, which is 15.2% better than those with conventional YAG: Ce3+ phosphor. Due to stokes loss of energy transfer from Ce to Cr, and the decrease of photopic vision eye sensitivity, the luminous flux of YAG: Ce3+, Cr3+ coated LED is inevitablely lower than those with YAG: Ce3+ phosphor by 44%.From photometry and colorimetry measurement, the better performancese have been observed with sample prepared by Co-Precipitation method, followed by Sol-Gel method. The solid state reaction method did not bring out better performance as reported in other literature.