Synthesis And Luminescent Properties Of White Light Phosphors Based On Tungstate And Molybdate For LED

Light-emitting diode(LED)can convert electric energy into luminous energy.Because of its long life,small size,safety and environmental protection,the market demand is increasing year by year.And it is considered as a new generation of solid-state light source.The light emitted by LED chips is monochrome.To get white light,red,green and blue LED chips need to be packaged together,but the cost and heat dissipation problems are difficult to solve.The current solution is to coat a LED chip with phosphors.The phosphors absorb the light emitted by the chip and transform it into other colors,then white light is obtained.In the LED lamp,phosphors are key materials,so the study of phosphors used in white LED lamp has always been the research hotspot.Rare earth ions have abundant energy levels.When 4f electrons transfer from high energy level to low energy level,they can emit light of different wavelengths.Among many host,tungstate and molybdate have stable chemical and physical properties.And there is an absorption band in the 200-350 nm,which can transfer the ultraviolet energy to rare earth ions.Therefore,tungstate and molybdate are good matrices for phosphors.In this paper,several rare earth doped white phosphors were prepared using tungstate and molybdate as substrates by high temperature solid-state method and hydrothermal method.The structure and luminescent properties were also studied.A series of novel color-tunable single-phase Li Gd(MO4)2: Sm3+,Tb3+(M = Mo,W)phosphors was prepared by solid-state reaction technique.Their luminescent properties were studied.Adjusting the proportion of matrix and the energy transfer among activator ions offers an approach to tune emission colors.The energy transfer mechanism is dominated by quadrupole-quadrupole interaction.By this approach,single-phased white-light-emitting phosphors were successfully prepared.It may serve as a potential white-light-emitting near-UV-convertible phosphors in w-LED devices.Ba WO4: Tm3+,Dy3+ phosphors were successfully prepared via the facile solvothermal method.The reason for these morphological changes is based on the kinetic control of the reaction speed,which relates to the strong chelating abilities of ethylene glycol.And the peanut-like Ba WO4: Dy3+ has the strongest emission intensity.Moreover,the emission colors of Tm3+ and Dy3+ codoped Ba WO4 could be tuned from blue to white through tuning the energy transfer.And energy transfer efficiency from Tm3+ to Dy3+ increases gradually with increasing the Dy3+ doped concentration.The energy transfer mechanism for Ba WO4: Tm3+,Dy3+ phosphors is demonstrated to be electric dipole-dipole interaction.A series of Dy3+ and/or Sm3+ ions doped Li La(WO4)2 phosphors was prepared by a facile solid-state reaction method.And,their luminescent properties were studied.Under the excitation at 404 nm,the correlated color temperature gradually decreases with the increase of Sm3+ concentration.The warm white light were obtained in the co-doped phosphors Li La(WO4)2: 0.06Dy3+,y Sm3+.Two modes of energy transfer are discussed,which is non-radiative and radiative energy transfer.The non-radiative energy transfer mechanism is dominated by quadrupole-quadrupole interaction.A series of Zn WO4: Eu3+,M+(Li,Na,K)phosphors was successfully prepared by facile solid-state reaction at 800?.Their power XRD and luminescent properties were studied.The excitation spectra indicate that the phosphors are suitable candidate for the fabrication of deep UV Al Ga N-based LEDs.The emissions of Eu3+ in the Zn WO4: x Eu3+(x = 0.00,0.01,0.02,0.03,0.04,0.05)are gradually enhanced to an optimum at 0.02,then they decrease as a result of the formation of the Eu2(WO)4 impurity.After M+(Li,Na,K)co-doped Zn WO4: Eu3+,the intensity of emission spectra change obviously.The experiments show that Li+ ions can promote an energy transfer from WO42-to Eu3+.The emission color of the phosphors can be tuned from bluish green to white and eventually to red.Using Li+ as charge compensator to enhance the luminescence of rare earth,two series of Zn WO4-based phosphors doped with Sm3+ or Eu3+ were successfully prepared by high temperature solid-state method under 800? condition.Two single-phase white light phosphors were obtained.The phase and luminescent properties of the samples were tested,and the XRD of two white phosphors were refined.The XRD results show that the phosphors are single phase when doped at low concentration.The asymmetry of excitation spectra may be caused by three different bond lengths of W-O in the matrix.The luminescent color of phosphors without Li+ is bluish green,and red shift occurs when Li+ is introduced.Two white light single-phase phosphors were obtained by adjusting the doping concentration.