| Near infrared (NIR) light can be used in biological analysis, due to it have many advantages, such as deep tissue imaging,no damage to the tested substances, small background interference and high sensitivity. Nd3+, Yb3+, and Er3+ are the most reported NIR luminescence RE3+ ions. However, The luminescence in these phosphors arises from the parity forbidden transitions between the partially filled 4f orbitals of trivalent lanthanide ions. This forbidden nature leads to low absorption cross-section. The near infrared luminescent intensity of rare earth ions doped inorganic materials is still weak, and not reach the immunoassay requirement. One efficient way to increase the fluorescence of lanthanide ions is to incorporate a second doping ion, such as Ce3+. The excitation and ground state of Ce3+ is at the d and f shell level, respectively, and the d-f transition is an allowed transition. Hence, fluorescence of Ce3+ is more efficient than that of other lanthanide ions which have forbidden f-f transition. The aim of this work was firstly to prepare novel NIR luminescence materials doped with Nd3+, Yb3+, Er3+ and secondly to analyze the relationship between the emission wavelength of Ce3+ and the energy transfer efficiency. The experiments are as follows:The Ca3-x-ySc2Si3O12:xCe3+, yRE3+(RE3+=Nd3+,Er3+,Yb3+)phosphors were synthesized by conventional solid-state reaction in a reductive atmosphere. The struture of the phosphors were characterized by X-ray diffraction. The influences of Ce3+/RE3+ concentration on the spectrum shape, fluorescence intensity and fluorescence lifetimes were systemically investigated. The results show that the efficient energy transfer from Ce3+ to RE3+ is due to good overlap between Ce3+ emission band and RE3+ excitation bands, and the characteristic near-infrared luminescence of RE3+ is remarkably sensitized by co-doping of Ce3+. With optimized Ce3+ and RE3+content of x=0.1 and y=0.07, the Ca3-x-ySc2Si3O12:xCe3+,yRE3+(RE3+=Nd3+,Er3+,Yb3+)phosphor has the strongest near-infrared luminescence intensity, which is about 400 times stronger than that of sample with absence of Ce3+. The mechanism of the energy transfer from Ce3+ to RE3+ in Ca3-x-ySc2Si3Oi2:xCe3+, yRE3+(RE3+=Nd3+,Er3+,Yb3+)phosphors is also discussed briefly.Novel near infrared (NIR) phosphors CaS:Ce3+, Nd3+ were synthesized by a solid state reaction. The influences of Ce3+/Nd3+ concentration on the spectrum shape, fluorescence intensity were systemically investigated. The results show that the characteristic near-infrared luminescence of Nd3+ is remarkably sensitized by co-doping of Ce3+. With optimized Ce3+ and Nd3+ content of x=0.001 and y=0.005, the CaS:xCe3+, yNd3+ phosphor has the strongest near-infrared luminescence intensity.Novel near infrared (NIR) phosphors CaxSr1-xS:Ce3+, Nd3+ were synthesized by a solid state reaction. It is found that CaS:Ce3+,Nd3+ can give much stronger NIR emission than SrS:Ce3+?Nd3+. Further studies on CaxSr1-xS:Ce3+,Nd3+ indicated that both visible emission of Ce3+ and NIR emission of Nd3+were observably affected by Ca/Sr ratio. The energy transfer efficacy, which can be estimated from fluorescence lifetime of Ce3+, increased from 52% to 74% for the CaxSr1-xS:Ce3+,Nd3+(x=0 to 1) series, accompanied with a shift of maximal emission wavelength of Ce3+ from 482nm to 505nm, It is believed that overlap between emission spectrum of Ce3+ and excitation spectrum of Nd3+ plays an important role in determining the energy transfer efficacy, and sensitization of Nd3+ fluorescence emission should be more favorable for Ce3+ emitting in green or blue-greenish region than that in blue region. |
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