Investigation Of Preparation And Luminescent Properties Of The Red Emissive Phosphors For WELD

The white light emitting diode(WLED)has great potential in lighting devices due to higher brightness and lower cost. In recent years, the phosphor-converted WLED has become the most commonly used method in industry. However, this strategy faces serious problems of thermal quenching from increased environmental temperature, poor color rendition by lack of red component and so on. In this dissertation, we have studied the new red emission phosphors for high color temperature WLED. The temperature dependent characteristics of phosphors has been also concerned and discussed by co-doping of cations. The main results are as follows:1. Gd₂WO₆:Eu³⁺ phosphors were prepared with different Eu doping concentration by the solid-state reaction. The strong red emission intensity under excitation of 393nm and 464nm for all samples are observed and reaches to a maximum when the content of Eu³⁺ comes to 0.4mol. The decay curves display a single exponential decay law. Temperature influenced intensity decline of phosphors is explained by the diagram of Fonger and Struck.The influence of Mn²⁺ co-doping is also investigated. The dramatically attenuated PL intensity of phosphor is owe to the energy transfer from Eu³⁺ to Mn²⁺ by decay behavior analysis.2. A series of Gd₂WO₆:Eu³⁺ phosphors doping with different amounts of SiO₂ were synthesized. The replacement of Si⁴⁺ to Gd³⁺ results in a red shift of the charge transfer state (O-Eu). The calculatedΩ₂ by Judd-Ofelt theory increases with the doping of SiO₂ and gets to a maximum by 0.4mol concentration of SiO₂. We conclude that the replacement of Si⁴⁺ affects the site symmetry of Eu³⁺ ion and results in Eu³⁺ ions in more non-symmetry crystal environment.The temperature dependent characteristics of phosphors are investigated with different amount of SiO₂ additive. With temperature increasing, the emission intensity decreases and the decay time shortens. Compared with undoped samples, the thermal stability is improved because the activation energyâ–³E grows in by adding SiO₂.3. Mn⁴⁺ doped 3.5MgO-0.5MgF₂-GeO₂:Mn⁴⁺ phosphors were prepared via the solid-state reaction. Samples show strong absorbability both in the UV and blue ranges, after increased doping amounts of Al₂O₃, the deep red emission of phosphors enhances and reaches to a maximum when the content is 0.3mol.The activation energyΔE is calculated and adopted to characterize the thermal stability of all samples. With Al₂O₃ doping,ΔE value becomes larger, which indicates the improved thermal stability.