Preparation And Luminescence Of The Borate Phosphor For White LEDs

Because of the low preparation temperature,outstanding stability and luminescence efficiency,borate phosphors are good luminescence material candidates for white Light Emitting Diode(LED).It is meaningful to preparate novel single-host borate phosphors.In this thesis,three series of borate phosphors have been synthesized using solid-state reaction method.Their crystal structure and luminescence properties were investigated.The main contents are given as follows:White light emitting phosphor Ba2Mg(BO3)2:Ce3+,Eu2+,Na+ has been synthesized using solid-state reaction under 1100 ℃.The excitation spectra of this phosphors ranged from 250nm to 350nm,peaking at 296nm.Meanwhile the emission spectra consists of two bands peaking at 416 nm and 608 nm.Ce3+ emit broad and strong blue light under the excitation of 296nm.Moreover,Ce3+ could act as sensitizer to excite Eu2+ and then Eu2+ emits broad and strong red light.The results show that the mechanism of the energy transfer is belonging to electric dipole-dipole interaction.The effect of Ce3+,Eu2+ doping concentration on the emission intensity are discussed in detail.Different chromaticity coordinates are obtained for each phosphor,that is,the chromaticity coordinates of the designed phosphor is tunable for the white-emitting LED or for special purpose.The borate phosphor Ba2Ca(BO3)2:Ce3+,Eu2+,Na+ was prepared for the first time.Ce3+ emit broad and strong blue light ranged from 350 nm to 450 nm under the excitation of 340 nm.The broad emission band consists of two peak at 390 nm and 410 nm,corresponding to the transitions from the lowest 5d excited state to the spin-orbit split 4f ground states 2F5/2 and 2F7/2.Ce3+ could act as sensitizer to excite Eu2+.Eu2+ emits broad and strong green light,which peaking at 525nm,attributed to the typical 4f65d1→4f7 transition of Eu2+.The results show that the mechanism of the energy transfer is electric quadrupole-quadrupole interaction.The ratio of blue and green can be tuned by adjusting the relative content of Ce3+ and Eu2+.Because of lacking of red light,Mn2+ was doped to overcome this shortcoming.The emission spectrum has shown that the phosphor consist of three emission peaks with peak center located at 415 nm,515 nm and 625 nm,respectively.In this thesis,energy transfer between Ce3+、Eu2+ and Mn2+ were investigated indetail.The dependence of luminescent intensity,chromaticity coordinates and quantum efficiency of the phosphor on different contents of Ce3+,Eu2+and Mn2+ doped in host were also studied.By tuning the relative content of these three kinds of ion,white light emitting phosphor was obtained.The phosphor can be effectively excited by UV chip,and is a high performance single host white light emitting phosphor for white LEDs.