Preparation And Properties Of Eu²⁺?Dy³⁺ Doped Na_2xM_3-x?PO₄?₂?M=Ca,Sr,Ba,Mg? Phosphors

LEDs as new solid-state light sources have a greatly promising application in the field of lighting and display,owing to their good performances of low voltage,low energy consumption,long lifetime,environmental protection etc.As an indispensable component of LED devices,the performance of phosphors directly determines the application of LED.Recently,rare earth-doped phosphate optical materials have received much attention due to the outstanding thermal stability,low synthesis temperature and the strong absorption band in the near-ultraviolet region.A series of Na₂MMg?PO₄?₂:Eu²⁺?M=Ca,Sr,Ba?phosphors were synthesized by the high-temperature solid-state reaction.The structure and luminescence of the samples were characterized by X-ray diffraction?XRD?,GSAS structural refinement,photoluminescence?PL?,lifetimes and thermal stability.Rietveld refinements of powder X-ray diffraction patterns of Na₂CaMg?PO₄?₂ confirm that the structure of Na₂CaMg?PO₄?₂ consist of stacking along the[001]direction.The Ca²⁺cations are located within the interlayer space,while Na⁺is found in a mount of cavities bounded to the layers.Upon excitation at 350 nm,the phosphors exhibit the asymmetric broadband emission peaked at about 392 nm attributed to the 4f⁶5d¹?4f⁷ transitions of Eu²⁺,and the Eu²⁺concentration corresponding to the maximal emission intensity is 0.01mol.It is found that when Ca²⁺sites are substituted by Sr²⁺or Ba²⁺,the Eu²⁺emission band shifts to a longer wavelength initially and then returns to a shorter wavelength.In particular,89.5%of the room-temperature emission intensity is still maintained at 500 K,indicating a good thermal stability.In addition,Na₂CaMg?PO₄?₂:Dy³⁺was synthesized by the high-temperature solid-state reaction.Under excitation of 350 nm,two strong peaks centered at 482 nm and 574 nm corresponding to the ⁴F_9/2?⁶H_15/2transition and the ⁴F_9/2?⁶H_13/2 transition.And white light emission?x=0.28±0.05,y=0.28±0.05?was achieved by changing the concentration of Dy³⁺.The Ca₃?PO₄?₂:Eu²⁺phosphor was synthesized by high temperature solid phase method.Under excitation of 365 nm,the emission peak of Ca₃?PO₄?₂:Eu²⁺is centered at about 415nm,and the experimental optimal Eu²⁺doping concentration in Ca₃?PO₄?₂:Eu²⁺is found to be 0.04 mol.It is found that when Ca²⁺sites are substituted by Sr²⁺or Ba²⁺,the luminescence spectrum is broadened and can be red shifted to about 520 nm.The package test of Ba_xCa_3-x?PO₄?₂:Eu²⁺showed that the color of the luminescence can be adjusted from blue to yellow-green as x changes.In addition,Ca₃?PO₄?₂:Dy³⁺was synthesized by the high-temperature solid-state reaction.White light emission?x=0.28±0.05,y=0.28±0.05?was achieved by changing the concentration of Dy³⁺.It is found that when Ca²⁺sites are substituted by Sr²⁺or Ba²⁺,the color coordinates of Ca₃?PO₄?₂:Dy³⁺will gradually move away from the white light region.