Preparation And Research On Luminescence Properties Of Double Vanadates And RE-molybdates Phosphors

White light emitting diode?LED?has been paid more attention due to its high efficiency,low power consumption,long lifetime and environmental benefits.Currently,two main methods are used to achieve white LEDs.One is to combine a blue LED chip with yellow-emission phosphor;the other is to pump three phosphors RGB?red,green and blue?with a UV or near-UV LED chip as the excitation source.The former exhibits poor color rending index and high color temperature because of the lack of red light emission.With regard to the latter,the major challenge is to explore high efficient red phosphors that match well with the near-UV LED chips,and to solve the reduced efficiency caused by the absorption of emission light between different materials.So,it is of great importance to search for novel red phosphors or single-phase white-light emitting phosphors.In the present work,we have synthesized several serials of K₃Gd?VO₄?₂:Eu³⁺,Y₂Mo₄O₁₅:Dy³⁺,Eu³⁺ and Gd₂Mo₄O₁₅:Eu³⁺ phosphors.The properties of the as-prepared samples are analyzed systematically via such as X-ray powder diffraction?XRD?,scanning electronic microscope?SEM?and photoluminescent?PL?et.al,and the results are as follows:1)A series of K₃Gd?VO₄?₂:Eu³⁺ phosphors were firstly synthesized via the solid state reaction method.An intense CT band centered at 314 nm and a strong red emission at 617 nm are observed in the PL spectra.The luminescence intensity can be enhanced by increasing the concentration of Eu³⁺ ions,until the optimal concentration of 50 mol%,the concentration quenching occurs,and then the intensity decreases with the increasing concentration of Eu³⁺ ions.The higher concentration quenching is caused by the special inherent structural features of K₃Gd?VO₄?₂:Eu³⁺ phosphor.With appropriate varying the excitation wavelength from 314 nm to 346 nm,K₃Gd?VO₄?₂:Eu³⁺ phosphors can emit multicolor light with tunable hues covering red,warm white to green,and a warm white light is achieved under the excitation at 337 nm.The present phosphors may have potential applications as red and single phase white phosphors for LEDs in solid state lighting.2)A series of novel color-tunable Y₂Mo₄O₁₅:Dy³⁺,Eu³⁺ phosphors were successfully synthesized via solid state reaction method.Y₂Mo₄O₁₅:Dy³⁺ phosphors show the characteristic emission of Dy³⁺ ions with blue(⁴F_9/2?⁶H_15/2),yellow(⁴F_9/2?⁶H_13/2)light,The yellow to blue emission?Y/B?ratio is about 0.9.The optimal concentration of Dy³⁺ ion in Y₂Mo₄O₁₅:Dy³⁺ phosphors is 8 mol%.The energy transfer from Dy³⁺ to Eu³⁺ ions is observed from the analysis of the emission spectra and decay curves.Y₂Mo₄O₁₅:xDy³⁺,yEu³⁺ phosphors can emit multicolor light with tunable hues covering green,white to orange-red by varying the concentration ratio of Dy³⁺ to Eu³⁺ ions,and a white light is achieved when the concentration of Dy³⁺ and Eu³⁺ ions is 8 mol%and 5 mol%,respectively.3)Novel pure-phase Gd₂Mo₄O₁₅:Eu³⁺ phosphors were successfully synthesized via solid-state reaction method.In the Gd₂Mo₄O₁₅ host crystal,there exist the[MoO₄],[MoO₅]as well as[MoO₆]groups.The excitation spectra of Eu³⁺-doped Gd₂Mo₄O₁₅ phosphors contains a broad charge transfer band ranging from 210 to 440 nm,which covers the UV and near-UV regions.Eu³⁺ ion locates at a low symmetry site.Under the excitation of UV,NUV or blue light,Gd₂Mo₄O₁₅:Eu³⁺ phosphors show red light emission at 618 nm.The optimal concentration of Eu³⁺ ions in Gd₂Mo₄O₁₅ phosphors is around 50 mol%,and the main concentration quenching mechanism is determined to be the exchange interaction.