Preparation,Analyses Of Structures And Optical Properties Of Ce-Doped Yttrium Aluminum Garnet Fluorescent Materials

YAG:Ce3+ phosphor powder was prepared by both solid state reaction method and sol-gel method.And the YAG:Ce3+ single crystals were grown by an optical floating zone furnace.The microstructures of the fluorescent materials were characherized by XRD and SEM.The phase transition of the YAG:Ce3+ powder was analysed by a differential thermal analyzer(TG/DTA).The photoluminescence spectra of the fluorescent materials were measured by a PL spectrometer.The optical properties the fluorescent materials prepared by different methods were investigated.The WLEDs were encapsulated by using InGaN as its blue light emitted chip,and YAG:Ce3+ powder or YAG:Ce3+single crystal prepared by different methods as its phosphor.The light emission intensities and the white light emission color coordinate from the WLEDs encapsulated with different phosphors were measured.The main experimental results are as follows:(1)YAG:Ce3+ phosphor powder were prepared by solid-state reaction method sintered at different temperatures.The XRD results of the YAG:Ce3+phosphor powder showed that the YAM phase(Y4Al2O9)was found in the sample sintered at 1200?.The YAP phase(YAlO3)was the main phase in the sample sintered at 1300?.The YAG phase(Y3Al5O12)was found in the sample sintered at 1400?.The YAG phase was the main phase in the sample sintered at 1550?,and the YAM and YAP phases were almost disappeared in this sample.As the sintering temperature increasing,the amount of the YAG phase in the sample increased,while the amounts of the YAM and YAP phases in the sample decreased.(2)YAG:Ce3+ phosphor powder was prepared by sol-gel method,the gel was sintered at 800?,900?,1000 ? for 3h,respectively,and then light yellow YAG:Ce3+ phosphor powder was ready.The SEM images indicated that the grain size of the YAG:Ce3+ phosphor powder increases with the sintering temperature.The XRD results of the YAG:Ce3+ powder showed that there was no YAG phase in the sample sintered at 700?,the sample was in amorphous form.There is only a single YAG phase in the sample sintered at 800?,and the YAM and YAP phases were almost disappeared in this sample.That is,as the sintered temperature increasing from 700? to 800?,the phase of the powder was changed from amorphous directly to YAG phase.Comparing the YAG phase formation temperature prepared by solid state reaction method with that by sol-gel method,it was found that the YAG phase formation temperature prepared by sol-gel method was 600? lower than that by solid state reaction method.(3)The XRD results of the YAG:Ce3+ single crystals grown by optical floating zone furnace indicated that there is only a single YAG phase in the YAG:Ce3+ single crystal.(4)The photoluminescence spectra of he YAG:Ce3+ powder prepared by sol-gel method sintered at different temperatures were measured by PL spectrometer when the samples were excited by a light with a wavelength of 460 nm.The experimental results showed that the intensity of the photoluminescence spectrum of the YAG:Ce3+ powder sintered at 700? was very week,because there is no YAG phases in this sample,the sample was in amorphous form.There was a strong emission peak in the photoluminescence spectrum of the the YAG:Ce3+ powder sintered at 800? and it was located at 530 nm in the yellow region,because the YAG phase was the main phase in the sample.The emission peak at 530 nm was corresponded to the transitions of Ce3+ ions from 5d to 4f.The intensity of the emission band increased with sintering tempwrature.(5)The photoluminescence spectra of the YAG:Ce3+ powder prepared by solid state reaction method sintered at different temperatures were measured by PL spectrometer when the samples were excited by a light with a wavelength of 460 nm.The experimental results showed that the intensity of the photoluminescence spectrum of the YAG:Ce3+ powder sintered at 1200? was very week,because there is no YAG phases in this sample,the sample was main YAM phase.There was a strong emission peak in the phot(?)luminescence spectrum of the YAG:Ce3+ powder sintered at 1400? and it was located at 530 nm,because the YAG phase was the main phase in the sample.The intensity of the emission peak increased with sintering temperature.(6)YAG:Ce3+ powder prepared by solid state reaction method was calcinated again in the air,N2,reduction atmosphere of C at different temperatures.Then,the photoluminescence spectra of these YAG:Ce3+ powder were measured by PL spectrometer when the samples were excited by a light with a wavelength of 460 nm.The experimental results showed that the intensity of the photoluminescence spectrum of the YAG:Ce3+ powder calcinated in the reduction atmosphere of C was the highest,that in the N2 was the next,while that in the air was the lowest.When the YAG:Ce3+ powder was calcinated in the reduction atmosphere of C,the Ce4+ was changed into Ce3+,due to the reduction reaction,and then increasing the the concentration of Ce3+in the sample,thus enhancing the intensity of the photoluminescence spectrum of the sample.(7)The photoluminescence spectra of the YAG:Ce3+ single crystals prepared by optical floating zone method were measured by PL spectrometer when the samples were excited by a light with a wavelength of 460 nm.It was found that there was a very strong emission peak located at about 530 nm in the photoluminescence spectrum of the the YAG:Ce3+ single crystal.(8)Comparing the photoluminescence spectra of the YAG:Ce3+fluorescent materials prepared by different methods,it was found that the intensity of the emission peak of the YAG:Ce3+ single crystal prepared by optical floating zone method was the highest,that prepared by solid state reaction method was the next,while that prepared by sol-gel method was the lowest.(9)The WLED was encapsulated by using the YAG:Ce3+ powder prepared by sol-gel method sintered at 900 ? as its phosphor materials,using the GaN/InGaN as its blue light emitted chip.The GaN/InGaN chip emitted a blue light with a wavelength of 450nm,when YAG:Ce3+ powder was excited by this light,a yellow light with a wavelength of abou 530nm was emitted from the powder.And then the white light was emitted from the LED due to the mixture of lights from the GaN/InGaN chip and the YAG:Ce3+ powder.(10)The WLED was also encapsulated by using the YAG:Ce3+ powder prepared by solid state reaction method and then calcinated again in the reduction atmosphere of C at 1400?,1450?,150? and 1550? for 8h as its phosphor materials,using the GaN/InGaN as its blue light emitted chip.It was found that on increasing the calcinating temperatures,the intensity of the emission light from the powder increased,and the wavelength of the emission light got red-shift.The increase of the calcinating temperatures of the YAG:Ce3+ phosphor powder would change the white light emission colors coordinate and then improved the color rendering.(11)The WLED was encapsulated by using the YAG:Ce3+ single crystal prepared by optical floating zone method as its phosphor materials,using the GaN/InGaN as its blue light emitted chip.The YAG:Ce3+ single crystal was a yellow and transparent piece,it emmited a very strong light with wavelength of 530 nm when it was excited by a light with a wavelength of 450 nm coming from the GaN/InGaN chip.And then the white light with rather strong intensity was emitted from the LED due to the mixture of lights from the GaN/InGaN chip and the YAG:Ce3+ single crystal.(12)Comparing the intensities of the white light coming from the WLEDs encapsulated by using different phosphor materials,it was found that intensity of the white light coming from the WLED encapsulated by using YAG:Ce3+single crystal as its phosphor material was the highest,that encapsulated by using YAG:Ce3+ powder prepared by solid state reaction method and then calcinated again in the reduction atmosphere of C at 1550? for 8h as its phosphor material was the next,while that encapsulated by YAG:Ce3+ powder prepared by sel-gel method sintered at 900 ? as its phosphor material was the lowest.