In this paper,luminescence thermal quenching of M2SiO4:Eu^2+(M=Sr,Ba) orthosilicate phosphors and mechanisms for thermal quenching proposed by different authors are briefly reviewed.Depending on preparation conditions...In this paper,luminescence thermal quenching of M2SiO4:Eu^2+(M=Sr,Ba) orthosilicate phosphors and mechanisms for thermal quenching proposed by different authors are briefly reviewed.Depending on preparation conditions and/or Eu^2+-doping concentrations,the quenching temperature(T1/2) and activation energy for thermal quenching of the same orthosilicate phosphor reported by different authors are inconsistent.The common conclusion is that T1/2 of the intermediate compound(Ba1-xSrx)2 SiO4:Eu^2+(x≈0.5) is higher than that of either Sr2So4;Eu^2+or Ba2SiO4;Eu^2+end-member.Moreover,T1/2 of the best-performing SrBaSiO4:Eu^2+is evidently lower than that of YAG:Ce3+and some Eu^2+-doped nitride phosphors.Rega rding the quenching mechanism,most of the investigators attributed thermal quenching to a thermally assisted 4f-5d cross-over in the configuration coordinate diagram.Only a few authors ascribed thermal quenching to a thermally assisted photoionization of 5 d electron to conduction band of the host.Nonetheless,a close inspection of T1/2 and Stokes shift derived from the vibrational spectra of the intermediate compound and end-member phosphors indicates that the 5d electron photo ionization model instead of the 4f-5d crossing decay model should be the genuine mechanism for the thermal quenching of M2 SiO4:Eu^2+(M=Sr,Ba) phosphors.Since the relationship between T1/2 and Stokes shift of the phosphors does not support the 4 f-5 d crossing decay model.The ionization probability of the 5 d electron depends on the energy gap(EdC) between 5 d1 level of the Eu^2+and conduction band minimum(CBM) of the host at higher temperatures.Lattice thermal expansion would result in an elevating 5 d1 level of the Eu^2+along with a diminishing CBM of the host and as a consequence a reduction in EdC and an enhanced photo ionization probability at elevated temperatures.A less rigid lattice and hence a larger coefficient of thermal expansion of M2SiO4 hosts should be the physical origin of poorer thermal quenching properties of the orthosilicate phosphors.展开更多
文摘In this paper,luminescence thermal quenching of M2SiO4:Eu^2+(M=Sr,Ba) orthosilicate phosphors and mechanisms for thermal quenching proposed by different authors are briefly reviewed.Depending on preparation conditions and/or Eu^2+-doping concentrations,the quenching temperature(T1/2) and activation energy for thermal quenching of the same orthosilicate phosphor reported by different authors are inconsistent.The common conclusion is that T1/2 of the intermediate compound(Ba1-xSrx)2 SiO4:Eu^2+(x≈0.5) is higher than that of either Sr2So4;Eu^2+or Ba2SiO4;Eu^2+end-member.Moreover,T1/2 of the best-performing SrBaSiO4:Eu^2+is evidently lower than that of YAG:Ce3+and some Eu^2+-doped nitride phosphors.Rega rding the quenching mechanism,most of the investigators attributed thermal quenching to a thermally assisted 4f-5d cross-over in the configuration coordinate diagram.Only a few authors ascribed thermal quenching to a thermally assisted photoionization of 5 d electron to conduction band of the host.Nonetheless,a close inspection of T1/2 and Stokes shift derived from the vibrational spectra of the intermediate compound and end-member phosphors indicates that the 5d electron photo ionization model instead of the 4f-5d crossing decay model should be the genuine mechanism for the thermal quenching of M2 SiO4:Eu^2+(M=Sr,Ba) phosphors.Since the relationship between T1/2 and Stokes shift of the phosphors does not support the 4 f-5 d crossing decay model.The ionization probability of the 5 d electron depends on the energy gap(EdC) between 5 d1 level of the Eu^2+and conduction band minimum(CBM) of the host at higher temperatures.Lattice thermal expansion would result in an elevating 5 d1 level of the Eu^2+along with a diminishing CBM of the host and as a consequence a reduction in EdC and an enhanced photo ionization probability at elevated temperatures.A less rigid lattice and hence a larger coefficient of thermal expansion of M2SiO4 hosts should be the physical origin of poorer thermal quenching properties of the orthosilicate phosphors.
