Spectral Design Of Ca₄(PO₄)₂O Based White LEDs With High Color Rendering

The phosphors are the core material to achieve white light-emitting,which directly affects the spectrum and color rendering performance of the white LED light source,for the current white LED light source technology.In order to obtain WLED with high color rendering and adjustable color temperature,the research and development of single-phased phosphors with tunable color emission which can be excited by near-ultraviolet chips is particularly important.In this paper,using Ca₄(PO₄)₂O as host lattice,and RGB tri-color luminescence was achieved by doping Tm³⁺,Tb³⁺,and Eu²⁺rare-earth ions.The high-quality white light emission phosphors with tunable color temperature and high color rendering index have been successfully developed.Finally,the sample and the near-ultraviolet chip were combined as WLED devices.The specific contents of this thesis are as follows:(1)A series of Ca₄(PO₄)₂O:Tm³⁺phosphors have been synthesized by solid-state reaction method.The XRD results indicated that all the samples show the pure phase composition of Ca₄(PO₄)₂O.Under the excitation of 352 nm near-ultraviolet light,the blue emission peak of Ca₄(PO₄)₂O:Tm³⁺phosphor at 458 nm and 463 nm was attributed to ¹D₂?³F₄ and ¹G₄?³H₆transition of Tm³⁺ions,while the super broad emission band centered at 411 nm was originated from the oxygen vacancies in Ca4(PO4)2O crystal.The emission intensity of Tm³⁺ions attained the maximum value when the doped concentration was 3 mol%.(2)In order to further enhanced the intensity of red emission by the energy transfer from Tm³⁺?Eu²⁺,the Eu²⁺ions was introduced into Ca₄(PO₄)₂O:Tm³⁺phosphor.The XRD results indicated that all the samples show the pure phase composition of Ca₄(PO₄)₂O.The red emission peak of at 624 nm was attributed to 4f⁶5d¹?4f⁷ transition of Eu²⁺ions.The emission intensity of the Tm³⁺ions(at 458 nm)decreases monotonously with the increasing of Eu²⁺content from 0%to 3%and the emission intensity of Eu²⁺ions(at 624 nm)attained the maximum value when the doped concentration was 1.5%,and then decreased dramatically.The energy transfer between Tm³⁺and Eu²⁺ions can be further confirmed by the decay curves of Ca₄(PO₄)₂O:Tm³⁺,Eu²⁺phosphors.The energy transfer efficiency from Tm³⁺to Eu²⁺ions is 90.5%when Eu²⁺ions concentration was 7%.(3)The single-phased phosphors with tunable color emission which can be excited by near-ultraviolet have been developed by controlling Tm³⁺and Tb³⁺to the optimal doping concentration,and a series of Ca_3.945-y(PO₄)₂O:0.03Tm³⁺,y Eu²⁺,0.025Tb³⁺were prepared.Under near-ultraviolet excitation,Ca_3.945-y(PO₄)₂O:0.03Tm³⁺,y Eu²⁺,0.025Tb³⁺phosphors exhibit the white light with adjustable CCT(3426?10750 K)and high CRI(Ra>80)composed by RGB luminescence at 458 nm(Tm³⁺),545 nm(Tb³⁺),and 603 nm(Eu²⁺)emission band,and it can be achieved by the different Eu²⁺ions concentration.It is worth noting that the acquired white light with(0.3271,0.3136)is close to the one defined by CIE standard light sources C(0.31006,0.31616)when Eu²⁺ions concentration is 0.25 mol%.And the neutral white light with optimum CIE chromaticity coordinates of(0.34,0.321),CCT of5113 K and high CRI(Ra=91.1),when Eu²⁺concentration is 0.4 mol%.(4)The high-quality WLED devices can be obtained by combining the 365 nm near-ultraviolet chip with Ca₄(PO₄)₂O:0.03Tm³⁺,0.025Tb³⁺,0.004Eu²⁺ phosphors at the concentration of 7%.