Synthesis And Luminescent Properties Of Tungstate-Based Fluorescent Materials

Since the 1990s,LEDs have gradually replaced traditional lighting sources and gained a large market share due to their environmental-friendliness,high efficiency,long life,low energy consumption and small size.As the fourth-generation lighting source,LED has great potential for development and will make a significant contribution to energy saving and emission reduction.However,LEDs currently have higher production costs relative to energy-saving lamps that are common on the market,and commercially available yelow phosphors are limited in their use due to the lack of red light components.In order to obtain high quality LED lamps,it is necessary to study new fluorescent materials.The majority of the fluorescent materials are based on rare earth ions and Bi³⁺ions as activators.In recent years,rare earth ions and Bi³⁺ion doped tungstates have been widely used and studied due to their excelent physicochemical stability and good luminescent properties.In this thesis,the tungstate compounds were selected as the hosts,and Bi³⁺ions and rare earth ions were used as activators.A monochromatic green phosphor,a near-ultraviolet-excited yelow phosphor and a single phase white light phosphor that is effectively excited by ultraviolet light were synthetized by high-temperature solid state methods.The details are as follows:1.Bi³⁺doped Gd₃BWO₉ was synthesized by high temperature solid state method.The Gd₃BWO₉ substrate and Gd₃BWO₉:Bi³⁺can be effectively excited by the medium ultraviolet light and generate strong emission in the region of 425-625 nm.Gd₃BWO₉as a self-activated host plays an important role in improving the luminous efficiency of Bi³⁺ions.When the doping amount of Bi³⁺ions is 0.10,concentration quenching occurs,and the corresponding internal quantum yield is 27%.2.The introduction of Tb³⁺ions in the Gd₂W₃O₁₂ host enables a full range of substitution of Tb³⁺ions for Gd³⁺ions.Tb³⁺ion doped Gd₂W₃O₁₂ can generate strong green light emission under near-ultraviolet excitation.Due to the one-dimensional chain structure,concentration quenching occurs when the doping amount of Tb³⁺ions in the Gd₂W₃O₁₂ host reaches 75 mol%,and the corresponding internal quantum yield is 37.6%at the doping concentration.The chromaticity adjustment from green region to red region is achieved by simultaneously introducing Tb³⁺/Eu³⁺or Tb³⁺/Sm³⁺at Gd₂W₃O₁₂and appropriately adjusting the dopant ions.3.A fluorescent material doped with Dy³⁺at the site of Ca in Sr₂CaWO₆ which can be effectively excited by 310 nm ultraviolet light was prepared by high temperature solid phase reaction.The Sr₂CaWO₆ matrix produced a blue light emission of 449 nm under ultraviolet excitation at 310 nm,and the corresponding color coordinate was?0.18,0.16?.The intensity of the emission peak at 310 nm excitation can be adjusted by adjusting the concentration of Dy³⁺ions.Sr₂CaWO₆:Dy³⁺with a doping amount of 1mol%at the Ca²⁺site delievered single-phase white light emission.