Adjustable Light And White Light Emitting Of Eu³⁺/tb³⁺ Doped Double Tungstate Phosphors

White light-emitting diodes（LED）as an emerging replacement for conventional incandescent lamps and fluorescent lamps lights up the 21 st century.Researching the efficient phosphor which is used for W-LED is of great significance.Due to the ultraviolet/near-ultraviolet luminescence properties and good stability of tungstate,it can be used as an important luminescence material and it has potential value in the W-LED display devices or lighting applications.In this paper,Eu³⁺,Tb³⁺ were used as activators,Na_0.45La_3.16W₅O₂₀,NaYW₂O₈ and Na_0.5Gd_0.5WO₄ were chosen as the matrix materials.Several kinds of phosphors for W-LED were synthesized.The composition,structure and crystal of the samples were determined by DTA-TG,XRD,IR and the luminescent properties of the samples were studied by fluorescence spectrum.Eu³⁺,Tb³⁺ doped Na_0.45La_3.16W₅O₂₀ white light emitting phosphors were prepared by coprecipitation method.When the annealing temperature was between 600℃ and 800℃,monoclinic phase Na_0.45La_3.16W₅O₂₀ was appeared.When the annealing temperature was more than or equal to 900℃,monoclinic phase La2W3O12 was appeared.When the pH was less than 5,the sample contained WO₃.When the p H was more than or equal to 5,the sample was pure monoclinic Na_0.45La_3.16W₅O₂₀.Compared with Eu³⁺ or Tb³⁺ doped Na2WO4 phosphor we can get that the La³⁺ in the matrix could significantly enhance the luminescence intensity of Eu³⁺ and Tb³⁺.There was an energy transfer of Tb³⁺→Eu³⁺ in the obtained Na_0.45La_3.16W₅O₂₀: Eu³⁺,Tb³⁺ phosphor.At the excitation of 382 nm ultraviolet light,the luminescence colors of Na_0.45La_3.16W₅O₂₀: Eu³⁺ phosphors and Na_0.45La_3.16W₅O₂₀: Eu³⁺,Tb³⁺ phosphors can be respectively turned from blue,white to red and turned from green,white to red.This two kinds of phosphors all achieved white light emission,the Na_0.45La_3.16W₅O₂₀: Eu³⁺ phosphors can emit white light only when the Eu³⁺ doping amount was between 3% and 6%,but Na_0.45La_3.16W₅O₂₀: Eu³⁺,Tb³⁺ phosphors can emit white light in a wide range of rare earth doping amount which was Eu³⁺=Tb³⁺=2%¹0%.So,doping of the Tb³⁺ in Na_0.45La_3.16W₅O₂₀ can increase the white light adjustable range of the phosphor.Thus Na_0.45La_3.16W₅O₂₀: Eu³⁺,Tb³⁺ phosphor is more suitable for UV-excited W-LED phosphor.Eu³⁺,Tb³⁺ doped NaYW₂O₈ white light emitting phosphors were prepared by coprecipitation method.When the annealing temperature was between 600℃ and 800℃,the sample was mixed with NaYW₂O₈ and Y₂W₃O₁₂;When the annealing temperature was more than or equal to 800℃,the sample was pure tetragonal NaYW₂O₈ crystal.When the p H was less than or equal to 3,the sample was WO₃;When pH was equal to 10,the sample phase has been completely transformed into tetragonal NaYW₂O₈.Compared with Eu³⁺ or Tb³⁺ doped Na2WO4 phosphor we can get that the Y³⁺ in the matrix could significantly enhance the luminescence intensity of Eu³⁺ and Tb³⁺.There was an energy transfer of Tb³⁺→Eu³⁺ in the obtained NaYW₂O₈: Eu³⁺,Tb³⁺ phosphor.At the excitation of 382 nm ultraviolet light,the luminescence colors of NaYW₂O₈: Eu³⁺ phosphors and NaYW₂O₈: Eu³⁺,Tb³⁺ phosphors can be respectively turned from blue,white to red and turned from green,white to red.This two kinds of phosphors all achieved white light emission,the NaYW₂O₈: Eu³⁺ phosphors can emit white light only when the Eu³⁺ doping amount was between 2% and 6%,but NaYW₂O₈: Eu³⁺,Tb³⁺ phosphors can emit white light in a wide range of rare earth doping amount which is Eu³⁺=Tb³⁺=2%¹0%.So,doping of the Tb³⁺ in NaYW₂O₈ can increase the white light adjustable range of the phosphor.Thus,NaYW₂O₈: Eu³⁺,Tb³⁺ phosphor is more suitable for UV-excited W-LED phosphor.Eu³⁺,Tb³⁺ doped Na_0.5Gd_0.5WO₄ white light emitting phosphors were prepared by coprecipitation method.When the annealing temperature was 600℃ and 700℃,the sample was monoclinic Gd2（WO4）3;When the annealing temperature was more than or equal to 800℃,the sample was pure tetragonal Na_0.5Gd_0.5WO₄ crystal.When the pH was equal to 3,the sample was mixed phases of WO₃ and Gd2（WO4）3;When the p H was more than or equal to 6;the sample phase was tetragonal Na_0.5Gd_0.5WO₄.Compared with Eu³⁺ or Tb³⁺ doped Na2WO4 phosphor we can get that the Gd³⁺ in the matrix could significantly enhance the luminescence intensity of Eu³⁺ and Tb³⁺.There was an energy transfer of Tb³⁺→Eu³⁺ in the obtained Na_0.5Gd_0.5WO₄: Eu³⁺,Tb³⁺ phosphor.At the excitation of 382 nm ultraviolet light,the luminescence colors of Na_0.5Gd_0.5WO₄: Eu³⁺ phosphors and Na_0.5Gd_0.5WO₄: Eu³⁺,Tb³⁺ phosphors can be respectively turned from blue,white to red and turned from green,white to red.This two kinds of phosphors all achieved white light emission,the Na_0.5Gd_0.5WO₄: Eu³⁺ phosphors can emit white light only when the Eu³⁺ doping amount is between 4% and 6%,but the Na_0.5Gd_0.5WO₄: Eu³⁺,Tb³⁺ phosphors can emit white light in a wide range of rare earth doping amount which is Eu³⁺=4%¹0% and Tb³⁺=10%.So,doping of the Tb³⁺ in Na_0.5Gd_0.5WO₄ can increase the white light adjustable range of the phosphor.Thus Na_0.5Gd_0.5WO₄: Eu³⁺,Tb³⁺ phosphor is more suitable for UV-excited W-LED phosphor.Finally,the results showed that La,Gd and Y are all favorable for the doping and emission of Eu³⁺ and Tb³⁺ in the matrix.The order of the influence on the light intensity of Eu³⁺ and Tb³⁺ is La> Gd> Y.In this paper,the alkali metal-rare earth double tungstate: Na_0.45La_3.16W₅O₂₀,NaYW₂O₈ and Na_0.5Gd_0.5WO₄ were selected as the matrix,and the luminescent materials which emit white light and which are adjustable in color were prepared by doping Eu³⁺ and Tb³⁺ ions.This can make the field of luminescent materials richer and provide information for the promotion of tungstate applications.