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Abstract: The upconversion luminescence spectral intensity of Er3+ in Er3+ and Yb3+ codoped ZnO nanocrystals with and without Li+ are investigated. Yb3+ ions as a tradition sensibilizer have efficient energy transfer processes from Yb3+ (2F5/2) to Er3+ (4I13/2, 4I11/2, 4F9/2), which lead to the increment of upconversion luminescence intensity. Following by adding Li+ to the Er3+ and Yb3+ codoped ZnO nanocrystals, the upconversion intensity emitted by Er3+ ions is found greatly enhanced. The enhancement is attributed to the distortion of the local field symmetry of Er3+ ions, so increases various intra-4f transitions of Er3+ ions. Both Yb3+ and Li+ can disperse Er3+ ions in specimen, so reduced the interaction between neighboring Er3+ ions. [Copyright &y& Elsevier]

Abstract: Er/Tm/Yb codoped Y2O3 nanocrystals and Er/Tm/Yb/Li codoped Y2O3 nanocrystals have been synthesized by sol–gel method, bright white light emission has been observed at 976nm excitation. The blue, green, and red emissions, respectively, arise from the transitions 1G4 → 3H6 of Tm3+, 2H11/2/4S3/2 → 4I15/2, and 4F9/2 → 4I15/2 of Er3+ ion. Moreover, after doping Li+ ions into Er/Tm/Yb codoped Y2O3 nanocrystals, the white light emission increase greatly. CIE coordinate of Er/Tm/Yb/Li codoped Y2O3 nanocrystals is X =0.32 and Y =0.36 at 10W/cm2 excitation, which is very close to the standard equal energy white light illuminate (X =0.33, Y =0.33). [Copyright &y& Elsevier]

Abstract: Infrared-to-visible upconversion luminescence spectra are investigated in Li+ and Er3+ codoped Y2O3 nanocrystals. By introducing Li+ ions, the upconverted emission intensity is found to be greatly enhanced when compared with the nanocrystals with the Li+ absent. The cause of the enhancement is believed to be the modification of the local symmetry of the Er3+ ion, which increases the intra-4f transitions of Er3+ ion, and the homogeneous distribution of Er3+. While in some other Er3+ doped oxides, such as ZnO, ZrO2, etc., the upconversion intensity of Er3+ ions could also be greatly increased by doping Li+. [Copyright &y& Elsevier]

Abstract: We demonstrate single band upconversion spectra of Er3+ and Yb3+ codoped ZrO2 nanocrystals. Ratios of green to red emission in Er3+ doped ZrO2 and red to green emission in Er3+/Yb3+ codoped ZrO2 are 8 and 10, respectively. Rate equations for rare earth energy level populations are used to investigate the upconversion mechanisms on the basis of the upconversion intensity dependences of pump power. Excited state absorption and energy transfer are the dominant processes in Er3+ doped and Er3+/Yb3+ codoped ZrO2, respectively. [Copyright &y& Elsevier]

Abstract: Variations of fluorescence intensity ratio of green (generated from Er3+ 2H11/2 and 4S3/2 levels) and red (generated from the sublevels of Er3+ 4F9/2 level) upconversion emissions in Er3+/Yb3+/Li+:ZrO2 nanocrystals have been studied as a function of temperature under 976nm laser diode excitation. In the temperature range of 323–673K, the maximum sensitivities of about 0.0134K−1 and 0.0104K−1 are obtained by using green and red emission, respectively. Er3+/Yb3+/Li+:ZrO2 nanocrystals show potential application value in nanoscale thermal sensor. [Copyright &y& Elsevier]