The Sr2 CeO4:Ln3+(Ln=Eu,Dy)fine phosphor particles were prepared by a facile wet chemical approach,in which the consecutive hydrothermal-combustion reaction was performed.The doping of Ln3+into Sr2 CeO4 has little influence on the structure of host,and the as-prepared samples display wellcrystallized spherical or elliptical shape with an average particle size at about 100-200 nm.For Eu3+ions-doped Sr2 CeO4,with the increase of Eu3+-doping concentration,the blue light emission band with the maximum at 468 nm originating from a Ce4+→O2-charge transfer of the host decreases obviously and the characteristic red light emission of Eu3+(5 D0→7 F2 transition at 618 nm)is enhanced gradually.Simultaneously,the fluorescent lifetime of the broadband emission of Sr2 CeO4 decreases with the doping of Eu3+,indicating an efficient energy transfer from the host to the doping Eu3+ions.The ene rgy transfer efficiency from the host to Eu3+was investigated in detail,and the emitting color of Sr2 CeO4:Eu3+can be easily tuned from blue to red by varying the doping concentration of Eu3+ions.Moreover,the luminescence of Dy3+-doped Sr2 CeO4 was also studied.Similar energy transfer pheno menon can be observed,and the incorporation of Dy3+into Sr2 CeO4 host leads to the characteristic emission of 4 F9/2→6 H15/2(488 nm,blue light)and 4 F9/2→6 H13/2(574 nm,yellow light)of Dy3+.The Sr2 CeO4:Ln3+fine particles with tunable luminescence are quite beneficial for its potential applications in the optoelectronic fields.
Na GaoYanfei YangShikao ShiJiye WangShuping WangJibiao LiLianshe Fu
Phase pure powders of SrCeO3 and Sr2Ce O4 have been synthesized by calcination at 1000℃for 14 h via solid state ceramic route.Ceramics/pellets of these samples have been obtained by sintering at 1200℃for 12 h.The Rietveld refinement of X-ray diffraction(XRD)pattern of sintered powders confirmed orthorhombic structure of both the samples with space group Pnma and Pbam for SrCeO3 and Sr2CeO4,respectively.Scanning electron microscopic(SEM)studies indicated that both the compounds have dense microstructure,but morphology and size of the grains are different.The impedance spectroscopy technique has been employed to study the relaxation phenomenon.DC conductivity of the samples has been measured in the temperature range of 200–600℃to understand the conduction mechanism.The activation energy for relaxation(Erelax)and DC conduction(Econd)are found to be the same for both the compounds.Based on the numerical value of activation energies,relaxation and conduction mechanism in both the samples are attributed to migration of doubly ionized oxygen vacancies(Vo··).Photoluminescence technique has been employed to confirm the existence of oxygen vacancies.These studies have indicated that migration of oxygen vacancies in Sr2CeO4 is occurring mainly along a and c direction,i.e.,via perovskite cells.Further,the present work has clearly indicated that besides optical properties,electrical properties of Sr2CeO4 are also interesting and can be utilized for various applications such as oxide ion conduction electrolyte in solid oxide fuel cells(SOFCs).
