Chao Mi

Efficient upconversion luminescence from Ba5Gd8Zn4O21:Yb3+, Er3+ based on a demonstrated cross-relaxation process

Under 971 nm excitation, bright green and red emissions from Yb3+/Er3+ co-doped Ba5Gd8Zn4O21 phosphor can be observed, especially the intense red emission in highly doped samples. The experimental results indicate that Ba5Gd8Zn4O21:Yb3+, Er3+ emits stronger upconversion luminescence than NaYF4:Yb3+, Er3+ under a low excitation power, and a maximum upconversion power efficiency of 2.7% for Ba5Gd8Zn4O21:Yb3+, Er3+ was achieved. More significantly, to explain the red emission enhanced with the dopant concentration, this paper presents a possible cross-relaxation process and demonstrates it based on the rate equation description and temporal evolution. In view of the strong upconversion luminescence, colour tunable ability and stable chemical nature, Yb3+/Er3+ co-doped Ba5Gd8Zn4O21 phosphor could be an excellent candidate for efficient upconversion luminescence generation.

Novel long persistent luminescence phosphors: Yb 2+ codoped MAl 2 O 4 (M = Ba, Sr)

The novel long persistent luminescence phosphors MAl2O4:Yb2+ (M = Ba, Sr) have been synthesized by a solid-state reaction. BaAl2O4:Yb2+ exhibits intense blue luminescence emission and the persistent time is even longer than the commercial phosphor SrAl2O4:Eu2+, Dy3+. The incorporation of Dy3+ ion as trap center evidently enhances persistent time of Yb2+ in SrAl2O4:Yb2+ host. We believe that MAl2O4:Yb2+ would replace the commercial SrAl2O4:Eu2+ as a new generation of long persistent luminescence materials due to the cheaper Yb2O3 than Eu2O3. To investigate the application in solar cell, MAl2O4:Yb2+ (M = Ba, Sr) phosphors are doped into methyl methacrylate monomer (MMA) polymer. The short circuit current density (Isc) of solar cell containing BaAl2O4:Yb2+ can easily be measured after removing the irradiation source.

Ultraviolet C upconversion fluorescence of trivalent erbium in BaGd 2 ZnO 5 phosphor excited by a visible commercial light-emitting diode

Multiple ultraviolet (UV) emission bands have been obtained in Er3+ doped BaGd2ZnO5 phosphor under the excitation of a 532 nm solid-state laser, and the emission peaks at 217, 254, 278, 296, 314, 348, 374 and 394 nm were determined to stem from the high-energy states 4D(1/2), 4D(7/2), 2H(9/2), 2P(1/2), 2P(3/2), 4G(7/2), 4G(11/2), 4H(9/2) of trivalent erbium, respectively. Some UV emission bands in the UVC region can be observed when the sample was excited by commercial green (529 nm) and blue (460 nm) LED. In view of the small size, low-drive voltage and price of LED, UVC upconversion phosphor BaGd2ZnO5:Er3+ excited by visible LED has potential application in environmental sciences.

A new method for measuring the refractive index of glass

It is well known in optics that the refractive index is an important optical parameter of material. A novel method to measure refractive index of glass has been reported in this paper. This method can be used to measure the refractive index of the special laboratory prepared glass which is small, irregularly shaped by measuring its absorption spectrum. And we have measured the refractive index of the laboratory prepared germanium-lead glass (1) (70GeO2-10Pb-10BaO -10K2O), germanium-lead glass (2) (60GeO2-20Pb-10BaO-10K2O)，germanium-lead glass (3) (50GeO2-30Pb-10BaO-10K2O) by measuring the absorption spectra of them with the new method. The experiment results show that the peaks position of the absorption shift forward the long wavelength and the refractive indexes increase with the increasing of Pb in germanium lead glasses. The above obtained refractive indexes are similar with the data which measured by the spectroscopic ellipsometry and the error less than 1%. The error analysis indicates that this method has high degree accuracy. We predict that the new method has a potential application in refractive index measurement for glass.