Study On Luminescence Properties And Energy Transfer Of Transition Metals Ions Mn⁴⁺ Or Bi³⁺ Co-doped With Rare Earth Ions In BaAl₂Ge₂O₈ And NaCaTiNbO₆

In recent years,with the rapid development of agricultural science and technol-ogy,the production technology is also rapidly progressing and plant lighting LED receives lots of attentions.As we all know,LED plant lighting needs to satisfy Pho-tosynthetic Action Spectrum(PAS).The PAS of plants shows that the characteristic absorption peaks of chlorophylls are 450-500 nm blue emission and 650-700 nm red emission.It is well know that Mn4+ doped phosphors give off red light ranging from 650 to 700 nm,which meets the red emission wavelength for plant lighting.In this thesis,BaAl2Ge2O8:Mn4+ deep red phosphors and BaAl2Ge2O8:Tb3+,Bi3+ co-doped green phosphors and NaCaTiNbO6:Pr3+,Bi3+ red phosphors were prepared by high temperature solid-state reaction method in air.The crystal struc-ture of sample are checked by X-ray Power Diffraction(XRD).The photolumines-cence and photoluminescence excitation spectra of the BaAl2Ge2O8 phosphor were measured to characterize the luminescence of the samples.The variable temperature spectrum of samples is used to characterize the thermal stability.The XRD patterns indicate that the structure of sample is unchanged after doping other ions.Excitation spectra of BaAl2Ge2O8:Mn4+ cover broad spectral region from 220 nm to 500 nm and have two absorption peaks at 288 nm and 435 nm,which owning to the Mn4+-O2-charge transfer band and the 4A2?4T1 and 4T2 transitions of Mn4+ ion.Emission band peaking at 658 nm and 668 nm in the range of 640-690 nm is attributed to the transition 2E ?4A2 of Mn4+ ion and the lattice vibrations.For BaAl2Ge2O8:Tb3+,Bi3+ co-doped phosphors,with the incorporation of Bi3+ions,the emission band of Tb3+ is significantly enhanced,this is partly because of the emission of Bi3+ itself,and the other part is attributed to the transition of 3P1-5D4 energy level from Bi3+ to the Tb3+,which does not transfer to the 5D3 level of Tb3+ due to the cross-relaxation phenomenon.Finally enhanced the emission of 5D4-7FJ.In NaCaTiNb06:Pr3+,Bi3+ samples,charge transfer of Nb067-and TiO68-groups and the energy transitions of SO?3P1 and 1S0?1P1 of Bi3+ ions and 1S0?1I6,3P0?3H4,1D2?3H4 of Pr3+ ions are superimposed,so the luminescence intensity of NaCaTiNb06:Pr3+ samples after co-doping Bi3+ ions is enhanced.Bi3+ ions have different roles in different matrix samples and have different luminescent properties.In the Bi3+ ion co-doped NaCaTiNbO6:Pr3+ sample,the Bi3+ ion does not emit light and acts as a sensitizer.In the sample of Bi3+ co-doped B&Al2Ge2O8:Tb3+,there is energy transfer between Bi3+ and Tb3+,which enhances the luminescence intensity of the sample.