Tailoring local coordination structure of the Er3+ ions for tuning the up-conversion multicolor luminescence.

The regulation of the local structure around Er3+ ions is an important channel for adjusting the characteristic of up-conversion luminescence. In this paper, the cubic-phased Er3+:CaF2 crystals with different Er3+ doping concentrations were fabricated with temperature gradient technique (TGT) method and the effect of the local coordination structure of the Er3+ ions on its luminescence performance was investigated. The local coordination structure of Er3+ ions was simulated by density functional theory. The computational results show that clusters evolve from low order to high order with the increase of Er3+ ion doping concentration. In this evolution process, the local structure transforms from cubic structure to the co-existence of cubic and lower symmetric square anti-prism structures. Meanwhile, the distance between Er3+ ions in the cluster decreased first and then increased slightly, and in dimers and trimers this distance reached the minimum. Under 980 nm excitation, with the increase of Er3+ ion concentration, the intensity ratios of the red and green emissions of Er3+:CaF2 first increased from 0.61 to 42.03 and then decreased to 12.11. The corresponding up-conversion luminescence gamut was adjusted from monochrome green to red to red-yellow. This work provides a new thread for realizing upconversion multicolor luminescence by regulating the clusters of rare earth ions.

[Water Chemistry and Characteristics of Dissolved Organic Carbon During the Wet Season in Wulixia Reservoir, SW China].

In recent years, scientists have focused on the karst carbon cycle. To better understand the hydrochemical characteristics and the physical-chemical properties of DOC in the wet season in karst areas, the water chemistry and DOC distribution characteristics in Wulixia reservoir were analyzed. The molecular weight of the water organic matter was analyzed based on the UV absorption spectrum. The results showed that the water chemistry of Wulixia reservoir was HCO3-Ca ·Mg, the nutrient status of the water body was of the medium nutrient type, and the water maintained a good quality. The DOC mass concentration was lower in the wet season than in the dry season, and DOC was the main component of TOC. The DOC mass concentration tended to decrease from the surface to the bottom in a vertical direction. Chl-a and DIC were the main factors affecting the DOC vertical distribution. The organic matter in the reservoir area related to the absorption spectrum parameters of S275~295, M, SUVA254, and E253/E203 showed that the water was dominated by constituents with small molecular weight, a high proportion of fulvic acid, low proportion of humic acid, and weak aroma. The results showed that the organic matter in the reservoir area was readily consumed by microbial bioactivity and that it played an active role in the carbon cycle of the reservoir. It also showed that the DOC endogenous characteristics of the reservoir were strong and provided a sufficient carbon source for heterotrophic microbes.

[Carbon Metabolism Characteristics of the Karst Soil Microbial Community for Pb-Zn Mine Tailings].

BIOLOG and 18S rRNA PCR-DGGE methods were used to estimate the characteristics of carbon source metabolism of the soil microbial community as well as the relationship between soil fungi and soil organic carbon in different karst land use types (corn field, citrus field, and paddy field) contaminated by Pb-Zn tailings at Sidi Village, Yangshuo, Guangxi Zhuang Autonomous Region, SW China. It was found that the concentrations of Pb, Zn, Cu, and Cd were highest in the paddy field, followed by the corn field, citrus field, and control group (dry field). In addition, the geo-accumulation index indicated that the heavy metal pollution at this area was caused by Pb and Cd and that Cd was the key environmental risk factor. With the Pb-Zn tailings, there was low microbial biomass carbon, biological entropy, and microbial carbon source metabolism in the soil samples. The highest soil organic carbon and heavy metal concentrations were found in the paddy field, followed by the corn field and citrus field. According to the DDGE results, it was found that Pycnoporus sp. ZW02.30 was found in control group soils, Fusarium solani and Fusarium oxysporum were found in the corn field and citrus field, and Penicillium decumbens was found in citrus field. These were involved in the degradation of sugars, such as starch, cellulose, hemicellulose, and lignin. However, the fungi were not found in the paddy field. Based on the low functional diversity of the soil microbial community and biological entropy as well as the high soil organic carbon concentration in the paddy field, it was concluded that soil microbial carbohydrate metabolism and the mineralization rate of the soil organic carbon was controlled by soil microorganisms, especially fungi, in different land use soils in the karst area contaminated by Pb-Zn tailings.