Synthesis And Energy Transfer Of Near Ultraviolet Excited Phosphors For WLEDs

At present,white light emitting diode（WLED）has become the common light source for lighting in the 21st century.With the development of near ultraviolet chip technology,it is of great significance to use near-ultraviolet In Ga N chip to excite single substrate white phosphors,but rare earth luminescent ions have sharp and narrow peaks,low utilization rate of light absorption,and cannot match well with near-ultraviolet chip,which seriously affects lumen efficiency and color reduction performance.Therefore,the purpose of this thesis is to find oxides with broadband absorption in the near ultraviolet region,using rare earth ion double doping to achieve white light emission in a single matrix,and using the composite structure to broaden the excitation spectrum of rare earth fluoride phosphor in the near ultraviolet region,a series of rare earth ion doped single-phase white light emission phosphors and composite phosphor were synthesized,and their energy transfer was studied.The main research contents are as follows.（1）A series of single garnet structure Na₂YMg₂V₃O₁₂:Dy³⁺,Eu³⁺(NYMVO:Dy³⁺,Eu³⁺)vanadate phosphors were prepared by solid phase reaction method.Under the near-ultraviolet light excitation of 365 nm,NYMVO:Dy³⁺,Eu³⁺phosphors simultaneously emitted sharp transition peaks of Dy³⁺ions at 487 nm in blue light region,576 nm in yellow light region,and red transition peaks of 595 nm,611 nm and 635 nm of Eu³⁺.The energy transfer processes among VO₄^3-,Dy³⁺and Eu³⁺were discussed.By changing the type and concentration of the doped rare earth ions,the emitting of the prepared samples can be multi-color adjustable and white emitting can be achieved.Temperature dependent emission spectra showed that NYMVO:Dy³⁺,Eu³⁺phosphors have high thermal stability.This phosphor can be used in the field of WLED with near UV excitation.（2）A series of Ba₂Gd₅B₅O₁₇（BGBO）:Bi³⁺,Tb³⁺,Sm³⁺borate phosphors were prepared by solid-phase reaction at high temperature.At the excitation wavelength of 365 nm,a transition emission peak at 418 nm attributed to Bi³⁺,the emission peaks of Tb³⁺at 489 nm,544 nm,and 620 nm transitions and 568 nm,604 nm,and 649 nm transitions of Sm³⁺were showed in the emission spectrum of BGBO:Bi³⁺,Tb³⁺,Sm³⁺phosphor.The energy transfer processes among Gd³⁺,Bi³⁺,Tb³⁺and Sm³⁺in BGBO:Bi³⁺,Tb³⁺,Sm³⁺phosphors were explored.Under the fixed Bi³⁺concentration of BGBO:Bi³⁺,Tb³⁺,Sm³⁺,the luminescent color of the phosphor can be changed from green to white and finally to orange by properly adjusting the doping content of Tb³⁺/Sm³⁺.Green and white orange adjustable BGBO:Bi³⁺,Tb³⁺,Sm³⁺phosphors show high efficiency emission and adequate thermal stability.This phosphor has potential in the field of near UV excited single phase white phosphor.（3）BaTiF₆:Mn⁴⁺@PVP-YF₃:Dy³⁺core-shell composite phosphors were synthesized by coprecipitation method.The emission peaks of Dy³⁺at 478 nm,572 nm and Mn⁴⁺at 635nm appeared concurrently in the emission spectrum of the composite phosphor under the excitation of 365 nm near ultraviolet light.The energy transfer process from Dy³⁺to Mn⁴⁺in composite phosphors was discussed.The composite phosphor can synchronously emit red,yellow and blue light when excited by near ultraviolet light.By adjusting the doping ratio of Mn⁴⁺and Dy³⁺,the polychromatic and tunable white-light of the composite phosphor can be achieved.This phosphor provides a new way for wide application in the field of WLED.