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Atmospheric nitrogen (N) deposition caused by anthropogenic activities may alter litter decomposition and species composition, and then affect N cycling and carbon (C) sequestration in an ecosystem. Using the litterbag method, we studied the effects of N addition (CK: no N addition; low-N: 1 g N m-2 y-1; high-N: 2 g N m-2 y-1) on changes in mass remaining of shoot litter decomposition of three grasses (Stipa baicalensis, Carex pediformis and Leymus chinensis) over 28 months in the Hulun Buir meadow steppe of Inner Mongolia. The results showed that the addition of high and low N had no significant effect on the decomposition of single-species litter, but low N addition slightly inhibited the decomposition of litter mixtures. In addition, litter decomposition was strongly species dependent. Our results suggest that species type is likely the main determinant of litter decomposition, and low N deposition in natural ecosystems does not influence single-species litter decomposition.

Er3+ and Yb3+ ions codoped calcium aluminum germanate glass has been synthesized by solid-state reaction. An intense infrared emission at 1534 nm, which corresponds to the minimum losses of silica based fibers used in optical communications, and visible emissions at 416, 490, 525, 548, and 660 nm, corresponding to the 4I13/2→4I15/2, 2H9/2→4I15/2, 4F7/2→4I15/2, 2H11/2→4I15/2, 4S3/2→4I15/2, and 4F9/2→4I15/2 transitions of Er3+ ions, respectively, were simultaneously observed in this glass under the excitation of a 978 nm diode laser at room temperature. These emissions are mainly attributed to energy transfer from Yb3+ ions to Er3+ ions. The up-conversion processes involve a sequential two-photon absorption for the red (660 nm), the green emissions (525 and 548 nm) and the blue emission (490 nm), and a sequential three-photon absorption for the violet-bluish emission (416 nm). The up-conversion fluorescence of Ca3Al2Ge3O12:Er,Yb glass can be used to detect 980 nm infrared laser light.

In this work, erbium-doped calcium aluminum silicate (CAS) glass has been synthesized by solid-state reaction. Intense emission at 1534 nm, corresponding to the 4 I 13/2 → 4 I 15/2 transition of the Er 3+ ion, was observed upon both 488 nm Ar + laser and 978 nm diode laser excitations at room temperature. The luminescence mechanisms in the glass are discussed. These results indicate this glass is a promising laser material with its high chemical durability and thermal stability.

In this work, a promising solid-state laser material, Er-doped cadmium aluminum silicate glass, has been synthesized by solid-state reaction. Very intense emission at 1534 nm, corresponding to the 4I13/2→4I15/2 transition of Er3+ ions, was observed upon both 488 nm Ar+ laser and 632.8 nm He–Ne laser excitations at room temperature. Possible cross-relaxation processes in the glass are discussed.

An efficient purplish–blue phosphor Ca3MgSi2O8:Ce3+ has been synthesized. The emission and excitation spectra of the Ce3+ ions in Ca3MgSi2O8 at 298 and 77 K indicate that there are two kinds of Ce3+ emission centers. According to the analysis of the crystal structure of the host and the spectral properties, we have demonstrated that the two kinds of emission centers correspond to Ce3+ substituting into two different octa-coordinated Ca2+ sites in the host, respectively.

Fluorescent spectra, excitation spectra, and fluorescence lifetimes are reported for a series of BaYF/sub 5/ crystals doped with Eu/sup 2 +/, Er/sup 3 +/, or Ho/sup 3 +/, or codoped with Eu/sup 2 +/ and either Er/sup 3 +/ or Ho/sup 3 +/ ions. These data were obtained as a function of concentration of active ions and temperature. The rate and efficiency of energy transfer between pairs of ions is obtained and the mechanism for energy transfer is found to be electric dipole-dipole interaction. In addition, multiphonon radiationless decay rates are determined for ER/sup 3 +/ in this host. 14 references, 12 figures, 2 tables.