Hydrothermal Synthesis And Luminescence Properties Of Rare Earth Borates And Fluorides

Owing to the growing importance of energy storage and environmental friendliness,much attention has been paid to the solid-state lightings （SSL） as the alternative to theexisting lighting technologies. The white lighting emitting diodes （WLEDs） havemany advantages, such as high energy efficiency, long life, good reliability andexcellent performance at low temperature. Generally, WLEDs are produced by mixingred, green and blue （RGB） LEDs, or combining the blue LED and yellow phosphor（Y,Gd）3（Al,Ga）5O12:Ce³⁺or using an ultraviolet （UV） LED-stimulated RGBphosphors. By means of the three methods, WLEDs with high efficiency, highchromatic stability and tunable color temperature, can be fabricated by UV-LED chipscoated with RGB phosphors. However, the lack of efficient red phosphors drasticallyhinders the development of the UV WLEDs.1、Pure Lanthanide orthoborate EuBO₃polycrystals were prepared by hydrothermalmethod. The crystal structure, morphology, valence state, luminescence property wereinvestigated via X-ray diffractometer, scanning electron microscope, X-rayphotoelectron spectrometer, and photoluminescence spectrometer. It is found that thecrystal structure of sample is hexagonal and the morphologies can be manipulated viausing different basicity. The orientation of the samples is along （100） and （002） whenNaOH and NH3·H2O is used as mineralizer, respectively. The luminescence band is tunableby varying the excitation wavelength. Red light can be generated for excitingat270nm because of mixed valence of the Eu, and EuBO₃presents blue emissionunder the excitation wavelength of360nm.2、GdBO3:Tm³⁺, Dy³⁺powder samples were synthesized under the low temperaturehydrothermal method. We can get different samples with tunablemicro-nanostructures structures via changing the basicity and temperature of thesynthesis conditions.The properties of the samples were analyzed by using X-raydiffractometer （XRD）, scanning electron microscope （SEM）, TG-DTA etc.measurements. The results show that all the samples were stable.The fluorescenceproperties of the samples were studied via using the Pl spectrum characterization. Theterms of the the luminescence properties between Dy³⁺-Gd³⁺ions, presents whiteemission when the excitation wavelength is278nm and the CIE chromaticitycoordinates locates at （0.3262,0.3427） after the Tm³⁺doped, and the ratio of Y/Bchanges at the Dy³⁺doped. These properties have potential applications. In WLEDs3、 The complex fluoride BaSiF₆: Tb³⁺,Eu³⁺were synthesized at180℃byhydrothermal method. The influences of molar ratios of initial mixtures, pH values,reaction temperature and reaction time on the products were investigated The resultsdemonstrates thatthe optimal reaction conditions were180-200℃, three days and thevalue of PH is3-4. Under the above conditions, we could get the pure compound.The properties of the sample were characterized in details. We investigated theinfluence of the structure and the compound of the product on the properties of thesamples. The SEM images show the length of BaSiF₆was3-12μm, the average grainsize was0.5-1.5μm. The product was white powder indicated that we could get thepure products with good crystalline.The fluorescent properties of the samples were studied. Eu³⁺doped BaSiF₆samples can emit bright red light under390nm UV light stimulate. Eu³⁺and Tb³⁺doped samples can get adjustable fluorescent emission. via changing the ultraviolet tothe near ultraviolet excitation wavelength. We can get close to white light at the excitation wavelength of370nm and390nm. All the results shows that this kind ofsamples can be used as a new type stimulate white LED phosphors near theultraviolet.