Preparation And Properties Of Rare Earth Doped Phosphate Luminescent Materials

Nowadays,white light-emitting diode（LED）is regarded as the fourth-generation light source following the incandescent,fluorescent and HID lamps.Because of its broad prospect in the field of lighting,the phosphor used in white LED has become a hot spot in the field of luminescence.A series of rare earth ion RE³⁺(RE= Eu³⁺,Tb³⁺,Dy³⁺,Sm³⁺)doped phosphors were synthesized by solid state reaction,in which Na₃Bi₂（PO₄）₃,Na₃Bi（PO₄）₂ and BiMg₂PO₆ played the roles as hosts based on the advantages of phosphate,such as stable chemical properties,no harm to the environment,low calcination temperature,simple synthesis and so on.The relationship between the crystal structure and luminescent properties was analyzed and studied in detail,which provided theoretical and experimental reference for the development of phosphor for white LED（1）A series of Na₃Bi_2-x（PO₄）₃:Re³⁺ and Na₃Bi_1-x（PO₄）₂:Re³⁺(Re=Eu³⁺,Tb³⁺,Dy³⁺,Sm³⁺)single doped phosphors were synthesized.After XRD test,it is found that the structure of Na₃Bi_2-x（PO₄）₃:Re³⁺ phosphors will change from Na₃Bi₂（PO₄）₃ to Na₃Bi（PO₄）₂ structure with the increase of rare earth ions doping concentration,but the structure of Na₃Bi_1-x（PO₄）₂:Re³⁺ phosphors will not change.From the measured XRD data and ion radius Bi³⁺（0.96?）≈Eu³⁺（0.96?）≈Sm³⁺（0.96?）>Tb³⁺（0.92?）> Dy³⁺（0.91?）,it can be inferred that the smaller the doping ion radius is,the less the original structure can be changed.Under near ultraviolet（n-UV）excitation at 396 nm,the main emission peak of Na₃Bi_2-x（PO₄）₃:Eu³⁺ phosphors is shifted from 621 nm to 598 nmwith phase transition,which also showed the emission that mainly from electric dipole transition converted to magnetic dipole transition.While the main emission peak of Na₃Bi_1-x（PO₄）₂:Eu³⁺ phosphors will not change and the emission is mainly frommagnetic dipole transition.Undern-UV excitation at 379 nm,Tb³⁺ doped phosphors show strong green emission and the strongest emission peak is located at 550 nmcorresponding to the 5D4-7F5 transition of Tb³⁺ ion.Undern-UV excitation at 392 nm,Dy³⁺ doped phosphors show strong yellow emission.The photoluminescence spectrum of Dy³⁺ ions is dominated by blue regions near 491 nm and yellowregions near 582 nm,which can be attributed to 4F9/2-6H15/2 transition and 4F9/2-6H13/2transition of Dy³⁺ ions,respectively.Undern-UV excitation at 407 nm,Sm³⁺ doped phosphors show strong orange-red emission and the strongest emission peak is located at 607 nmcorresponding to the 4G5/2-6H7/2 transition of Sm³⁺ ion.The results show that all the prepared phosphors have good absorption in the near ultraviolet region and have very important application value in the near UV white LED.（2）Eu³⁺-Tb³⁺/Sm³⁺/Dy³⁺and Sm³⁺-Tb³⁺doped Na₃Bi（PO₄）₂ phosphors with tunable color were synthesized.The energy transfer from Tb³⁺/Sm³⁺/Dy³⁺ to Eu³⁺ and Sm³⁺ to Tb³⁺ was obtained in the samples andit is found that the dipole-dipole interaction is the main reason for the energy transfer.Undern-UV excitation,the color of Na₃Bi（PO₄）₂: xEu³⁺,0.1Tb³⁺phosphors can be changed from green to red,the color of Na₃Bi（PO₄）₂: xEu³⁺,0.1Dy³⁺phosphors can be changed from yellow to red,the color of Na₃Bi（PO₄）₂: x Eu³⁺,0.1Sm³⁺phosphors can be changed from orange-red to red,the color of Na₃Bi（PO₄）₂: xSm³⁺,0.1Tb³⁺phosphors can be changed from green to yellow and then to yellow-white.In addition,the rare earth ions can enhance the red emission of Eu³⁺ ions through energy transfer process in Na₃Bi（PO₄）₂: yTb³⁺/zDy³⁺/lSm³⁺,0.1Eu³⁺phosphors.The results show that the prepared series of color tunable phosphors are expected to become a new type of near UV conversion phosphors,which is suitable for the needs of different special situations of white LED.（3）Eu³⁺,Tb³⁺,Sm³⁺,Dy³⁺doped and Zn2+ exchange BiMg₂PO₆ phosphors were synthesized.The excitation spectra and emission spectra of BiMg₂PO₆ host are broad spectrum.The strongest excitation peakand the strongest emission peak are located at 283 nm and 487 nm,which can be attributed to 3P1-1S0 transition and 1S0-3P1 transition of Bi³⁺ ions,respectively.UV at 283 nmcannot stimulate the luminescence of rare earth ions effectively in Eu³⁺,Tb³⁺,Sm³⁺,Dy³⁺ rare earth ions doped phosphors.Only in the near UV excitation can get the color of rare earth ions.The introduction of Zn2+ ions successfully enabled the excitation range of BiMg₂PO₆ to be extended from the ultraviolet region（283 nm）to the near ultraviolet region（372 nm）.When the Bi Mg2（1-x）PO6:xZn2+ phosphorsare excited by ultraviolet light,the main emission peak shifts from 487 nm to 500 nm.When the phosphorsare excited by n-ultraviolet light,it implements warm white emission with the main peak at 552 nm.