Preparation And Spectroscopic Studies Of Sm³⁺Doped Phosphate Red Phosphors

White light emitting diodes(WLEDs)are considered as one kind of new illumination light sources for their advantages of long working lifetime,high emission efficiency,and environmental friendliness.At present,the main way to fabricate white LEDs is to combine blue LED chips with yellow phosphors.However,the white light realized by this method has some drawbacks,such as low color rendering index and high color temperature due to lack of red light component.The near-ultraviolet LED chip excited WLEDs(NUV-WLED)have advantages of color stability and high color rendering index.The Y2O2S:Eu3+ phosphor is the common commercial phosphor currently as the red component for NVV-LED.But this phosphor has drawbacks of toxic and chemical instability.Sm3+ ion emits red light when it is excited by a near-ultraviolet LED.Phosphate has good properties such as stable physical and chemical properties,low production cost,and less harm to the environment.Therefore,Sm3+ activated Ba3Gd(PO4)3 phosphor has been studied in this thesis,and the subject research results are as follows:Ba3Gdz-x(PO4)3:xSm3+(X=0.02,0.04,...,0.12)phosphors were synthesized by high temperature solid-state reaction method.Ba3Gd(PO4)3:Sm3+ phosphors had strong absorption in the near-UV region.Under the excitation of 403 nm,it was observed that there were several emission peaks between 550-750 nm and the strongest emission peak located at near 598nm(4G5/2→6H7/2),and CIE chromaticity coordinates of the phosphors were(0.61,0.39),which located in the reddish orange region.The luminescence intensity of the phosphors increased with the increase of Sm3+ doping concentration until the Sm3+concentration reached 6.0 at.%,and then decreased with the further increase of Sm3+concentration.The concentration quenching Was caused by cross-relaxation between Sm3+.The fluorescence decay curve of the phosphor was further fitted by Inokuti-Hirayama model,and the intrinsic fluorescence lifetime of the 4G5/2 energy level of Sm3+ ions in Ba3Gd0.94(PO4)3:0.06Sm3+ phosphor was 4.38ms and the critical distance Rc was 10.61 A.The average fluorescence lifetime τavg of the 4G5/2 multiplet in the Ba3Gd0.94(PO4)3:0.06Sm3+ phosphor was 1.83 ms,which was less than the intrinsic lifetime,which also showed that the fluorescence lifetime of the 4G5/2 multiplet was affected by cross relaxation between Sm3+.Temperature dependent photoluminescence spectra of the Ba3Gd0.94(PO4)3:0.06Sm3+ showed that the integrated emission intensity of the 4G5/2→6H7/2 transition at 550 K decreased to 80.2%of that at room temperature and the activation energy of thermal quenching(△E)was calculated to be 0.142 eV.All the results showed that the Ba3Gd(PO4)3:Sm3+ could be a potential red phosphor for near-ultraviolet based white LEDs.