Research On Alkaline Earth Chloride Phosphors For White LED

With the development of white-LED and its gradually increased application rate, the research of phosphors for white-LED becomes more valuable. Alkaline earth chlorosilicate/chlorophosphate which was used as luminescence host has attracted much attention because of its stable crystal structure and high thermal stability. Here, the green-emitting phosphor Ca8Mg(SiO₄)₄Cl₂:Eu²⁺ and blue emitting phosphor Ca₂PO₄Cl:Eu²⁺ were prepared by solid state reaction and modified sol-gel method, respectively.First, Ca8Mg(SiO₄)₄Cl₂:Eu²⁺ were prepared by the modified sol-gel method. The factors those affect the luminescence intensity including heating temperature, the usage of the chlorine source CaCl₂ and the concentration of dopant Eu²⁺ were also investigated. The optimal synthesis parameters for the phosphor and the critical distance (Rc) of the energy transfer were concluded. As comparison, Ca8Mg(SiO₄)₄Cl₂:Eu²⁺ were also prepared by solid-state reaction. The excitation spectrum displays a broad band ranging from 375 to 450 nm and center at around 381nm, which match well with the emission of near UV/blue chips. The emission spectrum of phosphor shows a broad band at around 507nm. The phosphor prepared by sol-gel method shows brighter green emission than that of phosphor prepared with the same parameters using solid state reaction and the phosphor particle radius was smaller than that of the latter. The emission intensity was reduced when MgCl₂ replaced CaCl₂ as the chlorine source. M8Mg(SiO₄)₄Cl₂:Eu²⁺, (M=Ba,Sr,Ca) were also prepared and the Ca/Sr replacement makes blueshift in the emission peak.Phosphors Ca₂PO₄Cl:Eu²⁺ were prepared by solid-state reaction. The factors those affect the photoluminescence intensity including heating temperature, the holding time, the usage of the chlorine source CaCl₂ and the concentration of dopant Eu²⁺ were also investigated in detail. The excitation spectrum is a broad band covered 250-450nm which matches well with the avaliable near UV or blue emitting GaN-based LED chip. And Phosphor Ca₂PO₄Cl:Eu²⁺ shows brighter emission under the 400nm excitation than that of the commercial phosphor BAM:Eu²⁺, which makes it a potential candidate of blue emitting phosphor used for near-UV or blue light excited white LEDs.