Phosphor caused by LED darkening and bleaching problems have been broken

Reporters learned from the HeFei University of Technology 4, the School researchers in the study of LED fluorescent material made important progress, the results were published in the British "nature" published in the journal Science report.

High power LED devices are widely used in home and outdoor public lighting. However, when the LED light source is used for a long time, the problem of dimming and color drift occurs. Recently, Research Institute of materials science and engineering HeFei University of Technology associate professor Chen Lei and Professor Jiang Yang research group in the yttrium aluminum garnet LED series fluorescent material and color control mechanism and scientific mechanism of this phenomenon reveals, provides an important means to improve the performance of LED fluorescent material.

Due to high luminous efficiency and thermal stability is relatively good, yttrium aluminum garnet phosphor is the most widely used powder white LED device package, high power LED devices used in household lighting and outdoor lamps, almost all is formed by the fluorescent powder packaging. However, the use of the phosphor LED white light is a cold light, the comfort of the poor. In order to change the LED light color light from cold to warm, the most commonly used method is in yttrium aluminum garnet phosphor powder by gadolinium ion substituted Yttrium Ion, so that the phosphor emission wavelength, to reduce the color, the color index effect. However, the reduction of luminescence efficiency and the poor thermal stability will be caused by the substitution of yttrium ions by gadolinium ions. For this phenomenon, it is difficult to explain the classical coordinate model and molecular orbital hybridization theory for a long time.

Associate professor Chen Lei and his research group, through the comprehensive application of X X-ray absorption near edge structure, extended X ray absorption fine structure, ultraviolet photoelectron spectroscopy, X-ray diffraction, X valence band spectra and thermoluminescence fluorescence spectroscopy experimental methods, and combined with the electronic band structure, electronic density of States and the charge density difference calculation. From the electron cloud in the rigid structure deformation angle of Gd ion substitution spectra redshift, strength decrease and thermal stability caused by the variation of the intrinsic mechanism and give a new explanation. Because Gd larger ionic radius, the rigid structure of yttrium aluminum garnet will cause the electron cloud extrusion deformation, resulting in crystal field enhancement, the electron effective mass loss, spreading and expand the scope of electronic energy band gap decreases, which leads to the decrease of thermal stability and decrease luminous efficiency. Recently, the research results published in the British "nature" published in the journal Science report.

According to reports, this theory is not only a scientific explanation of the Gd substituted yttrium aluminum garnet phosphor luminous phenomenon, but also for the development of new rigid structure of fluorescent material has important guiding significance. "According to the establishment of this theoretical model, the future can also guide the development of the artificial gem crystal has a specific color, and give more bright and colorful color, such as a variety of artificial diamonds, sapphires and rubies, not only has high transmittance and reflectance, but also made specific color to bright eye-catching. Professor Chen Lei said.

For more information about LED, please click on China LED network or pay attention to WeChat public account (cnledw2013).