| Rare earth doped upconversion luminescent (UCL) materials have potential applications in solid state lighting and display, bio-label, solar cell and optical temperature sensor, et al. The focus of this paper is searching for novel efficient rare earth doped oxide UC material with high stability. Double molybdates were selected as the hosts and rare earth ions were used as activators. Their dependences of luminescence intensity on the synthesis method, technological parameters, host composition, dopant concentration, pumping power and other doped ions were studied systematically. The UC mechanisms, the tunable emission color and the enhancement of UCL efficiency of the phosphors were investigated intensively. The energy transfer processes from Yb3+to other rare earth ions were emphasized.Er3+, Yb3+codoped ALn(MoO4)2(A=Li, Na, K, Ag; Ln=La, Gd, Y) phosphor with green emission were prepared. The dependence of UCL intensity on the synthesis method, parameter, dopant concentration and matrices were investigated. Results indicate that the phosphors prepared by sol-gel method show stronger intensity than that of samples synthesized by solid state method. The strongest UCL intensity was obtained in LiLa(MoO4)2, and the tricolor (red, green and blue) UC emissions were obtained by co-doping different rare earth ions in this matrix. UC white light emitting were realized through adjusting the ratio of tricolor emission intensity by changing concentration of Ho3+, Tm3+and Yb3+.The UCL properties of rare earth doped CaIn2O4host with low phonon energy were investigated for the first time. CaIn2O4:Er3+, Yb3+phosphor with red and green bicolor emissions were synthesized. The increase of Er3+and Yb3+concentration leads to the increase of the ratio of red to green emission intensity, and tunable emission color could be obtained. The UC mechanism were illuminated and the energy transfer from Yb3+to Er3+were proved through comparison of UCL spectra of Er3+single doped and Er3+, Yb3+co-doped sample, the dependence of UC intensity on the pumping power and the fluorescence lifetime measurement.Ho3+single and Ho3+, Yb3+co-doped CaIn2O4with efficient UC green emission were synthesized. The influence of synthesis condition, dopant concentration and pumping power to the luminescent intensity were studied and the UC mechanism was discussed. The results indicate that the red emission is two photon process and the green emission includes two photon and three photon process. The UCL intensity of sample synthesized by sol-gel method is12times stronger than that of sample prepared by solid-state method. The introduction of Yb3+has enhanced the UCL of Ho3+greatly due to the effective energy transfer from Yb3+to Ho3+. The UC efficiency measurement of Caln2O4:0.1Yb3+,0.005Ho3+with optimal doping concentration indicates that the UC efficiency increases with the increasing of pump power and reaches the maximum value about5.5%at1.5W. This manifests that CaIn2O4:Yb3+, Ho3+is an efficient UC green emitting phosphor.CaIn2O4:RE3+and CaIn2O4:RE3+, Yb3+(RE=Tm, Pr, Nd) phosphors were prepared and their UC luminescent properties were investigated. The spectra comparison indicates that the the energy transfer from Yb3+to RE3+play an important role in the process of UC emissions of RE3+(Tm3+, Pr3+, Nd3+). The relation between intensity and pump power indicate that UC emissions of Tm3+, Nd3+are three photon process and UC emissions of Pr3+is the mixing of two and three photon processes under the excitation of980nm laser.Li+ions were introduced to Er3+, Yb3+co-doped CaIn2O4and UCL enhancement was achieved obviously. The possible reasons of the intensity enhancement include the charge compensation effect of Li+, the fluxing action of Li2CO3as well as the matrix distortion caused by Li+...
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