Tunable Direct-white Of Lanthanum Aluminate Phosphor For Led Via Valence State-controllable Means

Artifical white-light technology in lighting and display fields generally relies on the tri-color color-mix mechanism. Multi-component phosphors with different visible light emissions are used to combine white-light as excitated by ultraviolet (UV)/ near UV or blue light. A novel approach with single component direct-white-emission phopshors has attracted great attentions recently. In this M. S thesis, we explored another route of direct-white- emitting LaAlO_3-δ:Eu phosphor and adjustable strategy for color quality via valence control means. The important achievements obtained are summarized as follows.A. Photoluminescence of Eu³⁺ in single-doped LaAlO₃ host was investigated. It is found that,the color purity of red-light-emitting phosphor can be improved through increasing doped concentration once the cross relaxation in between Eu³⁺ was enhanced and the transition of Eu at higher energy level was surpressed.B. A direct-white regime of coexisting valence of Eu²⁺/Eu³⁺ in LaAlO_3-δ host was proposed. A combination by using intrinsic transition emissions of both Eu²⁺ and Eu³⁺ was successfully realized to generate direct-white light. Particularly, the 5D2�'7F2 transition of Eu³⁺ for green-light-emission positioned at 515 nm was recognized to play a key role to color-quality adjustment and its intensity could be enchanced with the aid of an efficient energy transfer between Eu²⁺ and 5D2 level of Eu³⁺.C. Quality of white-light emission from LaAlO_3-δ:Eu phosphor can be improved in some tunable means by optimizing synthesis parameters, doping charge compensation agent, co-doping alkaline earth ions and co-doping Mn²⁺. The photoluminescence variation with Sr-tunable and Mn-tunable means were investigated in details and found that desired color rendering index and correlated color temperature can be obtained upon codoping Sr and Mn. The descending of 5d electron in Eu²⁺ energy level due to O vancy results in efficient energy transfer and color adjustment for Sr-tuning, while a direct energy transfer exists in-between Eu and Mn for Eu-, Mn- co-adjustment.D. A bond-valence theory was employed to interpret mechanisms underlying phenomena of valence change and stability of Eu in some inorganic hosts. The coincidence of both theoretical and experimental results suggests that bond-valence theory is a effective tool to judge the stability of Eu valence state including what was concerned here. The investigation on valence state stability in this M. S thesis is of scientifical importance in the luminescence, and single component direct white phosphor LaAlO_3-δ:Eu investigated with tunable white-light-emission shows potential application in UV/nUV chip base white LED solid state lighting.