Luminescence Properties Of Eu Doped Silicate Phosphors For White LEDs

As an important component of solid state lighting field in the new century, white-light emission diode(W-LED) has attracted great attention due to its outstanding advantages such as energy saving, environmental protection and high luminescent efficiency, etc. So far. blue LED chips coated with a yellowish phosphor of YAG:Ce3+ have been invented by Japanese company, which is considered as the most widely used technique. However, developing novel phosphors are becoming more and more important due to patent issue and poor color rendering index caused by lacking of red component in emission spectra. In resent researches, Eu2+ ions doped alkaline earth silicates have been extensively investigated as excellent phosphor used for white LED due to its good properties for chemical and thermal stability, simplesynthesis technology. According to the discussion above, W-LED phosphors have been studied in this paper, and results show as follows:1. Sr2SiO4 phosphors are synthesized with different concentrations of Eu2+ ions through high-temperature solid-state reaction. The influence of different flux on the crystal phase and the luminescent properties of the sample are studied, and the boric acid is adopted as the best flux by analyzing the structure and spectra of samples. The mechanism of luminescence, the quenching concentration and the colorimetric performance are investigated based on the excitation and emission spectra. The Eu2+ ions show different luminescent properties while their occupying different Sr2+ sites by analyzing the spectra of the sample. The luminescent properties of the samples are greatly dependant on the excitation wavelength by analyzing the dependence of emission spectra and color coordinates on the excitation wavelength. The color coordinate of sample shows that the production has a potential application in W-LED field.2. Phosphors with compositions of SrO-MgO-SiO2:Eu are prepared in reducing atmosphere via high-temperature solid-state reaction technique. The impact on crystal structure, morphology, luminescent properties and colorimetric performance of the production are under study with varied SiO2 content. The results show that the phosphors prepared is confirmed to be a mixture of monoclinic Sr2SiO4 and orthorhombic Mg2(Si2O4), while SiO2 content does not affect the crystal structure of the samples. The scanning electron microscope images reveal that SiO2 content does not have any influence on the morphology of phosphors. On one hand, Eu2+ and Eu3+ ions co-existed in the phosphors when the SiO2 content is low, with EuJ3+ ions occupying the clearance of crystal lattice in the matrix and Eu2+ ions occupied two sites of Sr(I) and Sr(II) in compound of Sr2SiO4. On the other hand, with high SiO2 content, the Eu2+ ions can be easily doped into the sample due to the sufficient reaction, giving rise to strong emission intensity. The color coordinates are determined by the content of SiO2 as well as the excitation wavelengths.