Preparation And Study On Red Phosphors Based On White Light LED

\The fabrication and properties of phosphor used for white LED were paid more attention with the extension of applied field and the development of preparation technology in white LED. The phosphor-conversion white LED becomes the mainstream. Especially, the properties of phosphor excited by blue and near-ultraviolet light can effect directly the color rendering of white LED. The main purpose of this work is to obtained the phosphors for the near-ultraviolet based white LEDs. SrMoO₄: Eu³⁺,SrMoO₄: Sm³⁺ and SrMoO₄: Eu³⁺, Sm³⁺ were synthesized and their crystal structures, luminescent properties and energy-transfer process have been studied. The main contents and results are listed below.1. The SrWO₄: Eu³⁺ red phosphors have been prepared by co_precipitation method. Here, Sr （NO₃）₂、NaWO₄·2H2O、Eu 2O₃、HNO₃ and [C4H10O₃]n were used as source materials. The crystal structure, morphology and luminescent properties of the as-synthesized SrWO₄: Eu³⁺ were investigated. The x-ray powder diffraction and the scanning electron microscopy observations showed that the tungstate was body-centred tetragonal structure and the powder was nearly orbicular in shape, respectively. The as-synthesized SrWO₄: Eu³⁺ phosphors can exhibit sharply red characteristic emissions of Eu³⁺ at room temperature. The strong emission at 613 nm was observed, originating from the 5D0�'7F2 transition of Eu³⁺ ions. While monitoring 613 nm emission from Eu³⁺, the energy transfer was observed from the host to the Eu³⁺. The excitation spectrum of the SrMoO₄: Eu³⁺ red phosphors consisted of a broad band peak and a series of sharp peaks, which located at 281 nm （the broad band center）, 395 nm and 465 nm, respectively. This result shows that the as-synthesized SrWO₄: Eu³⁺ red phosphors can be effectively excited by the ultraviolet light emitting diode and blue light emitting diode. The absorption intensities of near-ultraviolet （395 nm） and blue light （465 nm） were controlled by adjusting Eu³⁺ doping concentration, and then the crystal constants, the crystal symmetries and the luminescent properties can be adjusted, respectively. This red emission had the characteristics of the high intensity and brightness, pure chroma. Compare with commercial Y₂O₂S: Eu red phosphors, the as-synthesized phosphors has higher luminescent intensity. 2. The SrWO₄: Sm³⁺ red phosphors have been prepared by co_precipitation method. Here, Sr （NO₃）₂、NaWO₄·2H2O、Sm₂O₃、HNO₃ and [C4H10O₃]n were used as source materials. The x-ray powder diffraction and the scanning electron microscopy observations showed that the as-synthesized SrWO₄:Sm³⁺ was a pure phase with body-centred tetragonal structure and this powder was nearly orbicular in shape, respectively. The as-synthesized SrWO₄: Sm³⁺ phosphors can exhibit sharply red characteristic emissions of Sm³⁺ at room temperature. The emission spectrum excited by 642 nm showed a strong emission peak at 597 nm, originating from the 4G5/2�'6H7/2 transition of Sm³⁺ ions. While monitoring 642 nm emission from Sm³⁺, the energy transfer was observed from the host to the Sm³⁺. Thus, the as-synthesized SrWO₄: Sm³⁺ red phosphors can be effectively excited by the ultraviolet （404 nm） light emitting diode and blue （480 nm） light emitting diode. The doped Sm³⁺ concentration has a great influence on the crystal orientation, crystal constants and the luminescent properties. The absorption intensities of near-ultraviolet and blue light were controlled by adjusting Sm³⁺ doping concentration, and then the red emission intensity under 404 nm and the 480 nm excitation can be adjusted, respectively. Compare with commercial Y₂O₂S: Eu red phosphors, the as-synthesized SrWO₄: Sm³⁺ red phosphors has higher color rendering index.3. A series sample of SrWO₄: Eu³⁺-Sm³⁺ phosphors have been prepared by co_precipitation method. Here, Sr （NO₃）₂、NaWO₄·2H2O、Eu 2O₃、Sm₂O₃、HNO₃ and [C4H10O₃]n were used as source materials. The red light emission of SrWO₄: Eu³⁺-Sm³⁺ was observed , which was excited by 250, 362 and 379 nm. The excitation spectrum consisted of two emission bands, which were attributed to Eu³⁺ and Sm³⁺, respectively. The energy transfer between Eu³⁺ and Sm³⁺ was observed. The light color can be tunable by varying the rare earth ions concentrations. The excitation wavelengths can affect the intensity ratio, and the doping concentration has a great influence on the crystal constants and the luminescent properties. Thus , the SrWO₄: Eu³⁺-Sm³⁺ phosphors can emit the white light by adjusting the doping concentration of Eu³⁺ or Sm³⁺, and excitation wavelengths, and then the color rendering index can be adjusted.