Crystal Structure And Luminescence Properties Of MRE₉?XO₄?₆O₂ Phosphor For W-LEDs

The white light emission by single ion doping or energy transfer process in a single host can well improve the luminescent properties of the phosphor.Meanwhile,red phosphors can improve the color rendering index of commercial white LEDs.It is very important to study the low-cost,high intensity and stable single-phase white phosphors and new red phosphors excited by near-ultraviolet or blue-light chips.In this paper,The crystal structure,electronic and luminescent properties of MRE₉?XO₄?₆O₂:Dy³⁺?M=Li,Na,K;RE=Gd,La,Y;X=Si,Ge?,LiGd₉?SiO₄?₆O₂:Sm³⁺/Eu³⁺and LiGd₉?SiO₄?₆O₂:Mn²⁺are developed.The effects of structural substitution on the crystal structure,electronic structure,luminescent properties,fluorescence lifetime decay as well as the thermal stability of the phosphors were also investigated.The main results are as follows:?1?A novel Dy³⁺doped white light emitting LiGd₉?SiO₄?₆O₂:Dy³⁺phosphor was prepared.Crystal structure was refined and the luminescence properties have been examined in detail.The band gap and electronic structure of LiGd₉?SiO₄?₆O₂ were performed by the density functional theory?DFT?calculation.Under the excitation at 350 nm,LiGd₉?SiO₄?₆O₂:Dy³⁺exhibited two main emission peaks in the visible wavelength region located at 477 and 573 nm,which is ascribed to the ⁴F_9/2-⁶H_15/2 and ⁴F_9/2-⁶H_13/23/2 transitions of Dy³⁺,respectively.The critical quenching concentration of Dy³⁺in LiGd₉?SiO₄?₆O₂ phosphor was determined to be about 0.10.?2?Phosphors of MGd₉?SiO₄?₆O₂:Dy³⁺?M=Li,Na,K?system substituted with alkali metal ions Li⁺,Na⁺and K⁺were prepared.The effect of alkali metal ion substitution on the structure and luminescent properties was investigated.The XRD results and structural refinement indicate the phase purity of the as-prepared samples.the effects of Li⁺,Na⁺and K⁺substitutions on the structure,luminescent properties and thermal stability of the phosphors of the system are discussed.As the alkali metal ion radius increases,the unit cell parameters of the system matrix samples gradually increase,and the yellow-blue ratio of the phosphors were also increase.?3?The effects of trivalent cations Gd³⁺,La³⁺,Y³⁺substitution on the structure and luminescence properties of LiRE₉?SiO₄?₆O₂:Dy³⁺?RE=Gd,La,Y?phosphors were investigated.In this system,the unit cell parameters of LiLa₉?SiO₄?₆O₂ substituted by the trivalent cation La³⁺ion were relatively increased.LiLa_8.9?SiO₄?₆O₂:0.10Dy³⁺have a relatively large yellow-blue ratio Y/B and relatively high thermal stability.?4?The effect of complex anion[[GeO₄]^4--[SiO₄]^4-substitution on the structure and luminescence properties of LiGd₉?XO₄?₆:Dy³⁺?X=Si,Ge?phosphors was investigated.The DFT calculation show that the band gap of LiGd₉?SiO₄?_6-x?GeO₄?_xO₂:Dy³⁺system decreases with the increase of x.The structure refinement show that the unit cell parameters of LiGd₉?SiO₄?_6-x?GeO₄?_xO₂ increase with the increase of x.The yellow-blue ratio Y/B of the emission spectrum of LiGd₉?SiO₄?_6-x?GeO₄?_xO₂ phosphors also increases with the increase of x.?5?Red emitting phosphors LiGd₉?SiO₄?₆O₂:Sm³⁺,Eu³⁺and LiGd₉?SiO₄?₆:Mn²⁺were synthesized and the crystal structure as well as luminescence properties were examined and studied.The photoluminescence investigations showed that LiGd₉?SiO₄?₆O₂:Sm³⁺phosphor emitted reddish emission,which ascribed to the transitions of the Sm³⁺from the ⁴G_5/2 excited state to the ⁶H_5/2,⁶H_7/2,and ⁶H_9/2 states,respectively.LiGd₉?SiO₄?₆O₂:Mn²⁺display an intense broad orange-red emission peaked around 594 nm,which ascribes to the typical spin-forbidden transition ⁴T₁?⁴G?-⁶A₁?⁶S?of the Mn²⁺ions.The energy transfer process between Sm³⁺and Eu³⁺were also discussed.