Preparation And Luminescence Characteristics Of Polytungsten/Molybdate Red Fluorescent Materials

Traditional incandescent lamps consume high power and are fragile,while wastes from fluorescent lamps contain mercury pollution.In comparison,white light-emitting diodes have various advantages of diodes:solid-state packaging,small size,low heat generation,high luminous efficiency,Long service life(more than 10,000 hours),rapid operation and start-up response,should not be damaged,simple device design,low production cost,low power consumption(low current and low voltage drive),no radiation,no escape of pollutants.Therefore,white light emitting diodes(WLEDs)will gradually replace incandescent and fluorescent lamps as a new generation of green lighting sources that meet environmental protection and energy saving requirements.At present,the industry related to white light LED is moving to a higher level,and the scientific research closely related to its application is being carried out at the same time.The development of green and blue phosphors is relatively mature.Therefore,in order to improve the luminous performance of white LED,it is of great significance to study the efficient and stable red phosphor powder,and more efforts should be put into the implementation of effective scientific practice.Tungsten-molybdate belongs to a self-activated fluorescent material.When tungsten-molybdate phosphor is excited by near-ultraviolet light,the charge transfer absorption band is not only wide but also high in strength,and it also has abundant electron transition from rare earth ions.The research in this paper mainly involves the following four aspects:(1)A series of Eu3+,Sm3+ co-doped Li3Ba2La3(WO4)8 phosphors were successfully synthesized by solid state method.all of them possess scheelite tetragonal crystal structure.The phosphor can be excited efficiently by near-ultraviolet(395nm)light and exhibit the strongest red emission peak of 616nm.The optimum doping concentration of Eu3+,Sm3+ions is determined to be x=0.09,y=0.03.Its chromaticity coordinate was observed to be(0.630,0.365).Sm3+ion as sensitizer can absorb energy effectively and transfer to the activator Eu3+ion,which lead to the enhancement of the luminous intensity of Li3Ba2La3-x-y(WO4)8:xEu3+,ySm3+ phosphors.(2)A series of Li3Ba2Tb3-x(WO4)8:xEu3+(x=0.01?0.06)red phosphors were prepared by a high temperature solid state reaction.The experimental results show that Eu3+ is well incorporated into the Li3Ba2Tb3(WO4)8 structure and becomes a good luminescent center,the phosphors can be efficiently excited by 487 nm light,and exhibit a red emissions corresponding to 5D?7F2 transitions of Eu3+at the main emission peaks of 616 nm.The variation of the emission spectrum indicates that there is an effective energy transfer of Tb3+to Eu3+with the change of Eu3+doping amount,and the fluorescence intensity reaches the maximum at x=0.05.The pyrophoric results of the phosphors showed that the fluorescence performance began to decrease obviously near 275?,indicating that the phosphors have higher thermal stability.(3)A series of Li3Ba2Tb3(1-x)(WO4)8:xSm3+(x=0.01,0.03,0.05,0.07,0.09)phosphors were synthesized by high temperature solid-state method.Analysing characterization results of the sample,it was found that when the phosphor was upon the 405nm excitation,there was a strong emission peak at around 647 nm which was assigned to the energy level transition of 4G5/2?6H9/2 of Sm3+ ions.When the rare earth Sm3+doping amount was 0.03,the sample had large luminescence intensity.As a result,the preferred doping amount of the rare earth Sm3+was 0.03.Under this condition,the color coordinate was(0.5391,0.449),and the color temperature was 2037 K.(4)A series of Lix+3Ba2Tb3(WO4)8-x(PO4)x:Eu3+(x=1?x=2?x=3?x=4?x=5? x=6)and Li5Ba2Tb3-x(WO4)6(PO4)2:xEu3+(x=0.20?x=0.40?x=0.60?x=0.80 ? x=1)were synthesized by high temperature solid-state method.When x=2 in Lix+3Ba2Tb3(WO4)8-x(PO4)x:Eu3+ phosphor sample,the intensity of the excitation spectrum of the sample reaches the highest.with the continuous increase of x,the intensity of the excitation spectrum of the sample begins to decrease,and the fluorescence lifetime decreases with the increase of phosphate doping amount.The introduction of Eu3+into the Li5Ba2Tb3-x(WO4)6(PO4)2:xEu3+phosphor sample did not change the crystal structure of the matrix.When x=0.6,the luminous intensity reaches the maximum,and the luminous intensity gradually decreases with the increase of temperature.