Phosphors And Devices In Application Of GaN-based Power WLEDs

Solid state lighting, especially white light emitting diodes (WLEDs), has been a worldwide fast-growing technology, for its advantages over traditional incandescent lamp in energy-saving, environmental friendliness and service life extension. High color rendering index (CRI) and power WLEDs are the directions of development in LED industry nowadays. In all the white light solutions, InGaN-based blue chip coated by posphors shows better efficiency and becomes the priority research area. To employ stable phosphors is a practical solution to power LED's instability.Focusing on novel Eu2+ -activated silicate and newly-discovered nitride phosphors in application of power WLEDs, the main achievements made in this work include:1) Phase-pure phosphors identified asα′-Sr₂SiO₄:Eu²⁺ andβ-Sr₂SiO₄:Eu²⁺ were obtained with sol-spray pyralysis procedure and solid reaction process for the first time, respectively.2) Differences in photoluminescent properties betweenα′- andβ-Sr₂SiO₄:Eu²⁺ were discovered. The photon energies from 5d-4f transition of Eu2+ were caculated using an empiciral Uitert formula, with results compared to actual ones from Guassian fitting method (489.1 nm/555.1 nm forα′- Sr₂SiO₄:Eu²⁺, and 468.8 nm/539.7 nm/593.2 nm forβ-Sr₂SiO₄:Eu²⁺). The peak at 593.2 nm is confirmed to be phosphorescent emission. Phosphors Ba₂SiO₄:Eu²⁺ and Sr3SiO5:Eu2+ with similar microstructure as Sr2SiO4 were prepared and evaluated.3) Highly efficient yellowish green nitride phosphor peaking at 534 nm with a broad excitation spectrum was prepared by solid state reaction precedure. Under excitation of blue light (460 nm), the unoptimizable phosphor shows a relative emission intensity about 51 percent of YAG:Ce3+.4) Compositions of nitride samples are studied according to XRD patterns; A possibe new phase is indexed and its parameters about unit cell are identified.5) Process parameters in preparing nitride phosphors were optimized, such as sintering temperature, reducing atmosphere, cation solid solution and co-activators. Effects of sintering temperature on spectra and morphology were also examined.6) Chromatic properties of those phophors were measured. Luminance ratio of phosphors needed in matching white light with different coherent color temperature (CCT) was given based on color-matching principle. Color rendering index (CRI) of the simulated light was evaluated as well. Some WLEDs were successfully packaged with those phosphors received from the experiments in the lab.