| Rare earth luminescent materials have a wide range of application in the field oflighting, display, X-ray radiation detection, and high-energy particle detection. YVO4has excellent thermal property, chemical stability, and a large absorption cross-sectionin the ultraviolet and the vacuum ultraviolet regions. In addition, its phonon energy issmall; thus, YVO4is often used as a photoluminescent matrix material. TheYVO34:Eu+phosphor exhibits a high quantum yield. This material, which often actsas the pink ingredient of display and lighting devices, has high commercial value.YVO4: Dy3+phosphor and YVO4:Tm3+phosphor has great potential in the field ofwhite and blue light emitting. The hydrothermal method was used to synthesizeYVO4:Dy3+phosphors as well as YVO4:Tm3+, YVO4:Dy3+/Tm3+, YVO4:Dy3+/Eu3+phosphors. In this paper, the structure and optical properties of the synthesizedphosphors are studied in detail. The main findings and innovations are listed asfollows:(1) YVO4:Dy3+phosphors were synthesized under different pH conditions. It isfound that the phosphors synthesized under strong acid and alkaline conditions arewell crystallized. The rod-like phosphors synthesized under strong alkaline conditionhave preferably luminescent properties. The doping of the rare-earth ions Dy3+in theYVO4crystal lattice introduces new vibration modes. The phosphors synthesizedunder different pH values have a UV absorption band from200to350nm. Theultraviolet absorption edge moves slightly with increasing pH and is maintained atapproximately320nm. The VO43+groups in the matrix material and the rare-earthions Dy3+have efficient energy transfer efficiency. A strong alkali environment isfavorable for the decrease of Y/B value of YVO4:Dy3+phosphors. The optimal dopingconcentration of Dy3+ions is1%for the YVO4:Dy3+phosphor. The YVO4:Dy3+spherical phosphors were synthesized by using sodium citrate as surfactant. However,the phosphors contain many organic groups, and seriously affect the crystallizationand emission characteristics of the phosphors. The porous specrical phosphors wereobtained after the anealing, and the crystallization of the phosphors improved significantly.(2) As the annealing temperature gradually increases, the crystallization of thephosphors becomes better. Meanwhile, the excitation band of VO3-4groups occursredshift gradually. With annealing temperature increasing, the emission characteristicsof the phosphors also become better. When the temperature annealing reaches800oC,the best emission characteristics of the phosphors were obtained.(3) The efficient energy transfer between the matrix material VO43-groups andTm3+ions also exist in the synthesized blue YVO4:Tm3+phosphors. The optimaldoping concentration of Tm3+is2%.(4) The double-doped YVO4:Dy3+/Tm3+phosphors were synthesized. DopingTm3+ions in YVO4:Dy3+phosphor enhances its blue emission intensity of thephosphor and obtains the white light-emitting phosphor. Finally, the chromaticitycoordinates of YVO4:2%(Dy3+0.2Tm3+0.8) phosphor is closer to the whitelight-emission region.(5) It is found that a reversible but different efficient energy transfer existsbetween two kinds of rare earth ions in the YVO4:Dy3+/Eu3+phosphors.The energytransfer from VO3-4groups to Dy3+/Eu3+ions, from Eu3+ions to Dy3+ions as well asfrom Dy3+ions to Eu3+ions are coexistence in the double doped YVO4:Dy3+/Eu3+phosphors. The efficiency of energy transfer from Eu3+ions to Dy3+ions is muchhigher than that from Dy3+ions to Eu3+ions. By means of multi-phonon absorptionand emission, Eu3+ions and Dy3+ions can achieve energy transfer throughnon-radiative transition. A small number of Eu3+ions can enhance the luminousintensity of Dy3+ions. When the concentration of Eu3+ions is more than0.75%, it canweaken the luminescence intensity of Dy3+ions. The emission of the phosphors isstill in the white light-emitting region when the concentration of Eu3+ions is small. |
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