The Photoluminescence Properties And Mixed Valence Of Rare-earth Tung States

White lighting emitting diodes (WLEDs) are promising due to their high energyefficiency, a long lifetime, a good reliability and environmental protection comparedto conventional incandescent lamps. It is well known that WLEDs are produced bymixing red, green and blue (RGB) LEDs, combing a blue LED with a yellowphosphor of (Y,Gd)3(Al,Ga)5O12:Ce3+or using near ultraviolet (UV) LED-stimulatedRGB phosphors. The major challenge in developing near UV LEDs is to explore highefficient tri-color phosphors that have the excitation wavelength matching well withthe emission spectrum of the near UV LED chips. Unfortunately, compared with blueand green phosphors, the current red phosphors based on Eu3+activated oxides,sulfides and nitrides have disadvantages such as low reliability and luminousefficiency. It is necessary to explore novel red-emitting phosphors that can beefficiently excited in the near UV range.The rare earth tungstates and molybdates can be effectively excitated by the blueand UV-LEDs now we use, which have high luminous efficiency and pure red color.In this work, we prepared a series of CaWO4-based red phosphors by hydrothermalsynthesis.1. We have synthesized a series of CaWO4-based red phosphors includingCa1-1.5xWO4:xEu3+(0.02≤x≤0.09), Ca0.925-ySryWO4:0.05Eu3+(0.1≤y≤0.9) andCa0.625Sr0.3W1-zMozO4:0.05Eu3+(0≤z≤0.7) by the hydrothermal method. Weinvestigated the photoluminescence properties, including the optimum dopingconcentration, excitation spectra, emission spectra, room temperature luminescencedecays and quantum yields of the phosphors. Our results demonstrate that theoptimum doping concentration of Eu3+, Sr2+and Mo6+is0.05,0.3and0.6, with thequantum yield of49%.2. A series of red phosphors co-doped with La3+, Sm3+, Ga3+and Lu3+ions weresynthesized by the hydrothermal method. We investigated the photoluminescenceproperties, including the optimum doping concentration, excitation spectra, emissionspectra and room temperature luminescence decays of the phosphors. Our results demonstrate that the optimum doping concentration of La3+, Sm3+, Ga3+and Lu3+is0.05,0.02,0.05and0.03.3. La-Doped Calcium Tungstate Ca0.72La0.28WO4was for the first timesynthesized by a one-step hydrothermal route at180℃in the presence of reducingagent of sodium borohydride. The La3+doped calcium tungstate shows thescheelite-type structure and mixed valence states of W5+and W6+. The blue shift inabsorption spectroscopy of the La3+doped calcium tungstate was observed andcomparison study was carried out for further exploring its structural features andphysical properties.