The green-emitting fluorescent powders of nano Y2O3：Er^3＋ were fabricated by the coprecipitation method. The X-ray diffrac- tion pattern shows that as-prepared Y2O3：Er^3＋ is the cubic phase crystal with a grain size of about 30 nm. The UV-Vis spec- trum indicates Y^O3：Er^3＋ exhibits five ultraviolet visible absorption peaks at 365, 377, 489, 521 and 652 nm respectively. Meanwhile, the fluorescence spectra of Y2O3：Er^3＋ display four emission peaks at 522, 537, 550 and 562 nm at the excitation of 365,377 and 521 nm, respectively. The green-emitting fluorescent mechanism of Y2O3：Er^3＋ is proposed as well. Additionally, the temperature dependence of fluorescence properties and metal Ag fluorescence enhancement effect are investigated. Results show that increasing the annealing temperature and metal Ag doping both can enhance the fluorescence intensity. The maxi- mum enhancement is 87.5% after Ag is doped.
JI RuoNanYE YanXiHU XiaoYunFAN JunLIU EnZhouZHANG QianZHAO ChaoShuaiYE SiWen
First-principles plane-wave pseudopotential calculations are performed to study the geometrical structures, for- mation energies, and electronic and optical properties of Y-doped, N-doped, and （Y, N）-codoped Ti02. The calculated results show that Y and N codoping leads to lattice distortion, easier separation of photogenerated electron-hole pairs and band gap narrowing. The optical absorption spectra indicate that an obvious red-shift occurs upon Y and N codoping, which enhances visible-light photocatalytic activity.
The three composites Y2O3 :Er3+ , Y2O3 :Er3+ /Yb 3+ andY2O3 :Er3+ /TiO2 were prepared using coprecipitation and sol-gel techniques. Their morphology, specific surface area, porosity, UV-vis. absorption spectra and fluorescence spectra were measured using SEM, TEM, surface analysis, UV-vis. absorption and photoluminescence spectrophotometry. SEM and TEM showed that samples prepared using coprecipitation were dispersed, while Y2O3 :Er3+ /TiO2 particles possessed a mesoporous surface and average diameter of about 10 nm. The specific surface area and porosity of Y2O3 :Er3+ /TiO2 did not result from the combination of the individual properties of Y2O3 :Er3+ and TiO2 . The specific surface area of Y2O3 :Er3+ /TiO2 was 135.991 m 2 /g and was 4.8 times that of Y2O3 :Er3+ and 2.5 times that of Degussa P25 TiO2 . A high specific surface area is conducive for application to TiO2 photocatalysis. The fluorescence spectra of the three composites exhibited three upconversion emission peaks with maxima at 237, 395 and 467 nm following excitation at 388, 500 and 570 nm, respectively.
YE YanXiLIU EnZhouHU XiaoYunYAN ZhiYunJIANG ZhenYiFAN Jun
