Yunfeng Bai

Upconverted photoluminescence in Ho3+ and Yb3+ codoped Gd2O3 nanocrystals with and without Li+ ions.

The upconversion photoluminescence of Ho(3+) ion sensitized by Yb(3+) ion in Ho(3+)/Yb(3+) codoped Gd(2)O(3) nanocrystals with and without Li(+) is investigated in this paper. Strong fluorescence in the green (534-570 nm) and red (635-674 nm) regions of the spectrum has been observed, arising from the (5)F(4)/(5)S(2) → (5)I(8) and (5)F(5) → (5)I(8) transitions of Ho(3+) ion, respectively. Yb(3+) ion is considered to be a better sensitizer for catching enough pumping energy and transferring considerable energy to Ho(3+) in the Ho(3+)/Yb(3+) system. The upconversion intensity emitted by Ho(3+) is greatly enhanced when Li(+) is added to the Ho(3+)/Yb(3+) codoped Gd(2)O(3) nanocrystals.

Effects of Li+ on structure and spectroscopic properties of Er3+/Li+ codoped Sb2O3―Na2O―SiO2 glasses

Judd–Ofelt (JO) analysis of Er3+ ions spectral properties in Er3+ doped and Er3+/Li+ codoped Sb2O3–Na2O–SiO2 glasses are performed based on the optical absorption spectra at room temperature. Three phenomenological parameters Ω2, Ω4, and Ω6 are determined. The effects of Li+ on the JO parameters are discussed in terms of the variations in Er3+ bonding nature and ligand fields around Er3+ sites.

Stark sublevels of Er3+–Yb3+ codoped Gd2(WO4)3 phosphor for enhancing the sensitivity of a luminescent thermometer

We report a strategy for enhancing the sensitivity of an optical thermometer by utilizing the Stark sublevels. Under 980 nm excitation, the upconversion emission originating from the Stark levels of Er3+ (4S3/2(2)/4S3/2(1) and 4F9/2/4F9/2(1)) is observed in a monoclinic phase Gd2(WO4)3:Er3+/Yb3+ phosphor, which is synthesized through the co-precipitation method. The temperature sensing behavior is studied over the range of 296–620 K based on thermal coupling levels 2H11/2/4S3/2(2), 2H11/2/4S3/2, 2H11/2/4S3/2(1), 4S3/2(2)/4S3/2(1) and 4F9/2(2)/4F9/2(1) using fluorescence intensity ratio (FIR) technology. The sensitivity based on Stark sublevels 2H11/2/4S3/2(2) or 2H11/2/4S3/2(1) is almost twice more than that based on the traditional 2H11/2/4S3/2 levels. The obtained maximum sensitivity of the optical thermometer is 16.5 × 10−3 K−1 at 395 K (2H11/2/4S3/2(2)). These results suggest that the use of Stark levels is a promising approach for enhancing the sensitivity of optical thermometers.

Upconversion photoluminescence and EXAFS of Er3+ and Ho3+ codoped with Li+ ion

Infrared-to-visible upconversion emission intensities are investigated in Li+/Er3+, Li+/Ho3+/Yb3+ and Li+/Tm3+/Yb3+ codoped oxide nanocrystals. By introducing Li+ ion, the upconversion emission intensity of rare-earth ions are significantly enhanced comparing with that without the Li+ ion. The local structure around Er3+ and Ho3+ ions are studied by the extended X-ray absorption fine structure spectroscopy. After doping Li+ ion, both the average bond lengths of Er-O and Ho-O are decreased.

High Thermal Sensitivity of Er3+ and Li+ codoped Y2O3 nanocrystals under 976 nm excitation

Er3+ and Li+ codoped Y2O3 nanocrystals has been prepared by sol-gel method. Upconversion spectrum and properties of Er3+ has been studied under excitation at 976 nm. Fluorescence intensity ratio of 2H11/2 and 4S3/2 subband levels in the Er3+ and Li+ codoped Y2O 3 nanocrystals have been studied as a function of temperature. In the temperature range of 295-723 K, the I525nm/I561nm has the highest thermal sensitivity the maximum sensitivity is approximately 0.016 K-1. The Y2O3: Er3+/Li+nanocrystals with high fluorescence efficiency and the higher temperature revolution, indicated that it is promising for applications in optical high temperature sensor.