Cubic NaYF4：Yb^3＋（20%）/Er^3＋（1%） microspheres were synthesized by EDTA-assisted hydrothermal method. Under 980 nm excitation, ultraviolet （^4G11/2→^4I15/2）, violet （^2H9/2→^4I15/2）, green （^4F7/2→^4I15/...Cubic NaYF4：Yb^3＋（20%）/Er^3＋（1%） microspheres were synthesized by EDTA-assisted hydrothermal method. Under 980 nm excitation, ultraviolet （^4G11/2→^4I15/2）, violet （^2H9/2→^4I15/2）, green （^4F7/2→^4I15/2, 2H11/2→^4I15/2, and ^4S3/2→^4I15/2）, and red （^4F9/2→^4I15/2） upconversion fluorescence were observed. The number of laser photons absorbed in one upconversion excitation process, n, was determined to be 3.89, 1.61, 2.55, and 1.09 for the ultraviolet, violet, green, and red emissions, respectively. Obviously, n=3.89 indicated that a four-photon process was involved in populating the ^4G11/2 state, and n=2.55 indicated that a three-photon process was involved in populating the ^4F7/2/^2H11/2/^4S3/2 levels. For the violet and red emissions, the population of the states ^2H9/2 and ^4F9/2 separately came from three-photon and two-photon processes. The decrease of n was well explained by the mechanism of competition between linear decay and upconversion processes for the depletion of the intermediate excited states.展开更多
A diamond p-n junction is used to convert the decay energy of 63Ni source into electrical energy. The selfabsorption effect of the 63Ni source, the backscatter process and the transport process of beta particles in di...A diamond p-n junction is used to convert the decay energy of 63Ni source into electrical energy. The selfabsorption effect of the 63Ni source, the backscatter process and the transport process of beta particles in diamond materials are studied. Then the theoretical maximum of electrical properties and the energy conversion efficiencies of diamond-63Ni p-n junction batteries are achieved. Finally, a feasible design of p＋p-n＋junction battery, which has the maximum output power density of 0.42 μW/cm2 and the optimal device conversion efficiency of 26.8%,is proposed.展开更多
Unusual intense infrared-to-ultraviolet upconversion luminescence was observed in YF3：yb3＋（20%）/Tm3＋（1%） nanocrystals under 980 ran excitation. The intense ultraviolet emissions （1I6→^3H6, ^1I6→3F4, and ^1D2...Unusual intense infrared-to-ultraviolet upconversion luminescence was observed in YF3：yb3＋（20%）/Tm3＋（1%） nanocrystals under 980 ran excitation. The intense ultraviolet emissions （1I6→^3H6, ^1I6→3F4, and ^1D2→^3H6） were affirmed arisillg from the excitation processes of five-photon and four-photon. In comparison with the bulk sample with the same chemical compositions, ultraviolet upconversion luminescence of the nanocrystals was markedly enhanced. Spectral analysis indicated that the enhancement was attributed to the decrease of Judd-Ofelt parameter Ω2, which precluded the transition rate from 3F2 to 3F4, enhanced the energy transfer process and populated the ^1D2 level： ^3F2→^3H6 （Tm^3＋）： 3H4→^1D2 （Tm^3＋）.展开更多
基金supported by the National Natural Science Foundation of China (10474096 and 50672030)
文摘Cubic NaYF4：Yb^3＋（20%）/Er^3＋（1%） microspheres were synthesized by EDTA-assisted hydrothermal method. Under 980 nm excitation, ultraviolet （^4G11/2→^4I15/2）, violet （^2H9/2→^4I15/2）, green （^4F7/2→^4I15/2, 2H11/2→^4I15/2, and ^4S3/2→^4I15/2）, and red （^4F9/2→^4I15/2） upconversion fluorescence were observed. The number of laser photons absorbed in one upconversion excitation process, n, was determined to be 3.89, 1.61, 2.55, and 1.09 for the ultraviolet, violet, green, and red emissions, respectively. Obviously, n=3.89 indicated that a four-photon process was involved in populating the ^4G11/2 state, and n=2.55 indicated that a three-photon process was involved in populating the ^4F7/2/^2H11/2/^4S3/2 levels. For the violet and red emissions, the population of the states ^2H9/2 and ^4F9/2 separately came from three-photon and two-photon processes. The decrease of n was well explained by the mechanism of competition between linear decay and upconversion processes for the depletion of the intermediate excited states.
基金Supported by the National Major Scientific Instruments and Equipment Development Project under Grant No 2012YQ240121the National Natural Science Foundation of China under Grant No 11075064
文摘A diamond p-n junction is used to convert the decay energy of 63Ni source into electrical energy. The selfabsorption effect of the 63Ni source, the backscatter process and the transport process of beta particles in diamond materials are studied. Then the theoretical maximum of electrical properties and the energy conversion efficiencies of diamond-63Ni p-n junction batteries are achieved. Finally, a feasible design of p＋p-n＋junction battery, which has the maximum output power density of 0.42 μW/cm2 and the optimal device conversion efficiency of 26.8%,is proposed.
基金supported by the National Natural Science Foundation of China (10474096 and 50672030)
文摘Unusual intense infrared-to-ultraviolet upconversion luminescence was observed in YF3：yb3＋（20%）/Tm3＋（1%） nanocrystals under 980 ran excitation. The intense ultraviolet emissions （1I6→^3H6, ^1I6→3F4, and ^1D2→^3H6） were affirmed arisillg from the excitation processes of five-photon and four-photon. In comparison with the bulk sample with the same chemical compositions, ultraviolet upconversion luminescence of the nanocrystals was markedly enhanced. Spectral analysis indicated that the enhancement was attributed to the decrease of Judd-Ofelt parameter Ω2, which precluded the transition rate from 3F2 to 3F4, enhanced the energy transfer process and populated the ^1D2 level： ^3F2→^3H6 （Tm^3＋）： 3H4→^1D2 （Tm^3＋）.
