Preparation And Characterization Of Bi And Eu-codoped Y₂O₃ Phosphor By Wet Chemical Methods

The light-emitting diode has many advantages,such as small size,less heat-releasing,energy saving,long lasting life,fast responding,free from contamination,possibility being flat-packaged.The phosphors with excellent performance could dramatically improve the luminescent efficiency of LED.In recent years,both Bi and Eu-codoped Y₂O₃ phosphor has been developed with a fantastic prospect of application.Having compared with and analyzed the existing synthesis methods,it is believed that precipitation method is the most possible to be used in industry to replace the existed solid state reaction method.The microwave-hydrothermal method is an energy-saving one,while the resulted powder is fine.In this investigation,the microwave-hydrothermal method was preliminary employed,and then the precipitation one was thoroughly investigated in preparing of both Bi and Eu-codoped Y₂O₃ phosphor.Fluorescence analysis can be used in qualitative analysis of entering the crystal lattice for some elements.In this investigation,both Bi and Eu-codoped Y₂O₃ phosphors were synthesized by both microwave-hydrothermal method and precipitation one,respectively.To analyze the effects of pH values,of the amount of the mixture of oxalic acid and ammonia precipitant,of the heat treatment temperature,the ion doping concentration, titration sequence and flux on the crystallization,topography and luminescent properties of the powder,the phosphors were characterized with DTA/TG/DTG, XRD,laser particle sizing,SEM,TEM & HRTEM,EDS,FTIR and fluorescence spectrophotometry and so on.The main results and achievements are as follows.The precursor prepared by microwave-hydrothermal processing was heat treated at 1100℃for 2h,resulting in(Y_0.94-x,Eu_0.06,Bi_x)₂O₃ phosphor.The particle shape of(Y,Eu)₂O₃ phosphor is rod-like,whereas the shape of(Y,Eu,Bi)₂O₃ is nearly spherical.This implies that the growth of the crystal face(211) might be restrained, resulting from Bi doping probably.The intensity of the emission spectra was generally enhanced when excited with 346nm electromagnetic wave owing to Bi doping.Actually,it was raised firstly,achieved a maximum when x=0.03,and then declined later on.These indicated that the phosphor powder may be able to serve in the case of near-UV band of 320nm～375nm electromagnetic wave.The precursor precipitated by both oxalic acid and ammonia as precipitants was heat treated for 2h,resulting in both Bi and Eu-codoped Y₂O₃ phosphor,which has particles with flake shape.The crystallization has been found to occur at 800℃already,when the precursor was heat treated.With heat-treating temperature increasing,the crystal morphology was improving,the particles were growing,and the intensity of the emission spectra was generally being enhanced.It is found that the temperature quenching happened at 1200℃.The peak position in the XRD pattern of the(Y_0.94,Eu_0.05,Bi_0.01)₂O₃ sample heated at vary temperatures for 2h was consistent with that in the XRD pattern of(Y,Eu)₂O₃ in JCPDF file,no change in the XRD pattern of the sample was observed.This is the same as that in the case of microwave-hydrothermal processing.The relationship of ion doping concentrations with the concentration quenching of the phosphor was investigated.Effects of the inverse titration method were compared with those of the titration one in precipitation processing on the luminescent properties.SEM images showed that the resulted particles were broken to pieces when the precursor was subjected to ultrasonic dispersing,compared with those without ultrasonic dispersing.Adding either H₃BO₃ or NH₄F flux was found to be able to enhance the intensity of the emission spectra of the phosphor,whereas adding H₃BO₃ achieved better results.