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Low threshold power density cw laser-induced heat has been observed in and codoped nanocrystals under excitation by a 980 nm IR laser. Codoped remarkably reduces the power density threshold of laser-induced heat compared with doped nanocrystals. When the excitation power density exceed , codoped nanocrystals emit strong blackbody radiation. The thermal emission of should originate from the multiphonon relaxation between neighboring energy levels. One additional UC-PL enhancement is observed. The UC-PL intensity can be enhanced by an order of magnitude through high temperature calcination caused by light into heat. [ABSTRACT FROM AUTHOR]

We investigate upconversion emissions in alkali metal ions (Li, Na, and K) and Er-codoped YO nanocrystals. By introducing Li, upconversion intensity is significantly enhanced, while Na and K hardly have this influence. FT-IR data give evidence that the main mechanisms of the enhanced upconversion emission cannot be attributed to the decreased surface defects. EXAFS data and variations of enhanced upconversion intensities in different samples indicate that Li can occupy the interstitial sites in lattice and thus arouse large site asymmetry. In addition, locations in the samples and effects on the upconversion emission of Na and K are discussed. [ABSTRACT FROM AUTHOR]

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: Infrared-to-visible upconversion emission spectrum is investigated in Li+, Ho3+ and Yb3+ codoped Y2O3 nanocrystals. By adding Li+ ion to the Y2O3:Ho3+/Yb3+ nanocrystal, the upconversion emission intensity is found being significantly enhanced comparing with that without Li+ ion. The two reasons for this enhancement are discussed: one is because of the modification of the local symmetry of the Ho3+ ion, and the other is because of the reducing number of OH groups. This indicates Li+ ion would be a wonderful photoluminescence intensifier for rare-earth. [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]

Er3+/Li+ co-doped Y 2 O 3 nanocrystals were synthesized by the sol-gel method. Fluorescence intensity has been enhanced about 270 times under 980 nm laser excitation by combined laser annealing (90 times) and co-doped with Li+ ions (3 times). The doping of Li+ ions increased the asymmetry around Er3+, while laser annealing reduced surface defects. Fluorescence characteristics with the temperature of laser annealed Er3+/Li+ co-doped Y 2 O 3 nanocrystals were studied. An interesting phenomenon that the non-thermal coupling of I 563 /I 799 transformed into the thermal coupling as the temperature rises is found. The possible mechanisms were discussed, and fluorescence thermometry based on I 563 /I 799 showed higher temperature sensitivity than other reports. The effective fluorescence enhancement method and the new fluorescence thermometry energy levels can promote the application of rare earth fluorescent materials. [ABSTRACT FROM AUTHOR]

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]

The SrMoO 4 :Yb 3+ /Er 3+ nanocrystals (NCs) were synthesized by sol–gel method. The upconversion luminescence properties of SrMoO 4 :Yb 3+ /Er 3+ NCs were studied in contrast to the identical dopants in Y 2 O 3 NCs under the same experimental conditions. The results demonstrate that the green emission intensity of the former is much stronger than that of the latter, while the red emission intensity is reverse. Interestingly, the green-to-red intensity ratio of SrMoO 4 :Yb 3+ /Er 3+ NCs increases with the increase of Yb 3+ concentration at fixed Er 3+ concentration. The anomalous luminescence properties of SrMoO 4 :Yb 3+ /Er 3+ NCs are attributed to the high excited state energy transfer (HESET) from the | 2 F 7/2 , 3 T 2 > state of the sensitizer Yb 3+ – MoO 4 2 − dimer to the 4 F 7/2 level of the activator Er 3+ . The HESET process can partly decrease the lattice phonon quenching processes at lower energy levels of Er 3+ and enhance the green emission dramatically. [ABSTRACT FROM AUTHOR]

Abstract: We demonstrate the upconversion-photoluminescence spectra of Er3+, Yb3+ and Li+ ions doped ZrO2 nanocrystals. By introducing Li+, emission intensities of single green and single red band increase by a factor of 1.93 and 1.65, respectively. Powder X-ray diffraction data and decreased slopes of the excitation power dependences on upconverted emission intensities give evidences that Li+ ions can tailor the local structure of host lattice and improve energy transfer processes from Yb3+ to Er3+, respectively. [Copyright &y& Elsevier]