Oxide-based Red-emitting Phosphors In Phosphor Converted White Light-emitting Diodes

Phosphor-converted white light-emitting diodes(pc-WLEDs) are emerging as an indispensable solid state light for the next generation lighting industry and display systems due to their unique properties such as high efficiency, low energy consumption, long lifetime, environmental benefit, fast response, and easy maintenance. To attain high color rendering white LED, the red-emitting phosphors are required. However, the currently commercial available red-emitting phosphors are low efficiency and chemically unstable. It is necessary to develop efficient red emitting phosphors for fabrication of white LEDs. In this dissertation, we focus on the preparation and properties of oxide-based red-emitting phosphors.Polycrystalline LaBSiO₅:Eu³⁺ phosphors have been synthesized by a facile sol-gel method. It is noted that the photoluminescence intensity enhances with the increasing Eu³⁺ concentration and the maximum emission intensity appears at 30 mol%. The red emission of La_0.7BSiO₅:Eu0.3 is enhanced by a factor of 2.5 and 3.6 as co-doping 2 mol% Bi³⁺ and 2mol% Sm³⁺, respectively.The Ca3(VO₄)₂:Eu³⁺ phosphors have been prepared by sol-gel method. The effect of compensator on optical properties of Ca_2.85(VO₄)₂:0.15Eu³⁺ is systematically investigated. It is obviously observed that the PL intensity of Eu³⁺ increases in the order of Ca_2.85(VO₄)₂:0.15Eu³⁺, Ca2.7(VO₄)₂:0.15Eu³⁺,0.15K+, Ca_2.775(VO₄)₂:0.15Eu³⁺, Ca_2.7(VO₄)₂: 0.15Eu³⁺,0.15Na⁺, Ca2.7(VO₄)₂:0.15Eu³⁺,0.15Li⁺. The introduction of Sm³⁺ into the phosphor Ca₃(VO₄)₂:Eu³⁺ can extend the excitation region to match the near-ultraviolet light emitting diode and enhance the luminescent intensity trough the energy transfer into Eu³⁺.The Ca₈MgLa(PO₄)₇:Ce³⁺,Mn²⁺ phosphors have been prepared by conventional solid state reaction under a weak reductive atmosphere. The phosphor Ca₈MgLa(PO₄)₇:Mn²⁺ shows red emission of 640 nm under 404 nm excitation. The energy transfer and the sensitized effect from Ce³⁺ to Mn²⁺ have been investigated. The energy transfer efficiency is found to increase gradually with the increasing Mn²⁺ content. The energy transfer from Ce³⁺ to Mn²⁺ is proposed to be resonance-type via an electric dipole-dipole mechanism.The Ba₃Gd(PO₄)₃:Ce³⁺, Mn²⁺ phosphors have been synthesized by conventional solid state reaction under a weak reductive atmosphere. The phosphor Ba₃Gd(PO₄)₃:Mn²⁺ shows red emission of 605 nm under 406 nm excitation. The energy transfer and the sensitized effect from Ce³⁺ to Mn²⁺ have been researched. The energy transfer mechanism is determined to be an electric dipole-dipole type.