Xiaoliang Yang

Up-conversion in Er3+:Y2O3 Nanocrystals Pumped at 808nm

Er3+ ion-doped Y2O3 nanocrystals were prepared by coprecipitation synthesis technique. Visible emissions at 650, 540, and 523nm have been observed under excitation at 808nm. Comparing with the stokes emission characteristics of the nanocrystals pumped at 488nm, the up-conversion mechanisms excited at 808nm have been investigated in detail. Excitation power dependent behaviors of the up-converted emission intensities indicate that a two-photon excited state absorption process is responsible for the S3∕24(H11∕22)→I15∕24 transition while a no-resonant energy transfer I9∕24+I11∕24→I9∕24+I13∕24 principally performs the red up-conversion of the F9∕24→I15∕24 transition.

Strain engineering of the elasticity and the Raman shift of nanostructured TiO2

Correlation between the elastic modulus (B) and the Raman shift (Δω) of TiO2 and their responses to the variation of crystal size, applied pressure, and measuring temperature have been established as a function depending on the order, length, and energy of a representative bond for the entire specimen. In addition to the derived fundamental information of the atomic cohesive energy, binding energy density, Debye temperature and nonlinear compressibility, theoretical reproduction of the observations clarified that (i) the size effect arises from the under-coordination induced cohesive energy loss and the energy density gain in the surface up to skin depth; (ii) the thermally softened B and Δω results from bond expansion and bond weakening due to vibration; and, (iii) the mechanically stiffened B and Δω results from bond compression and bond strengthening due to mechanical work hardening. With the developed premise, one can predict the changing trends of the concerned properties with derivatives of quantita...

Luminescence properties of rare earth doped YF3 and LuF3 nanoparticles

Eu3+ doped and Yb3+/Ho3+ codoped LuF3 and YF3 nanoparticles with a size distribution of 200–300 nm have been prepared by adopting a combustion-fluorization method. The luminescence spectra of Eu3+ and Ho3+ ions in the YF3 and LuF3 nanoparticles have been investigated through comparison. It is found that the Eu3+ and Ho3+ ions in the two hosts show different luminescence properties although the sites occupied by the rare earth (RE) ions in the LuF3 and YF3 hosts are of the same symmetry. The different luminescence properties may be ascribed to the difference in the RE-F bond nature in the YF3 and LuF3 hosts.

Conversion of broadband UV-visible light to near infrared emission by Ca14Zn6Al10O35: Mn4+, Nd3+/Yb3+

Efficient Ca14Zn6Al10O35: Mn4+, Nd3+/Yb3+ spectral conversion materials have been prepared by a sol–gel method. The Ca14Zn6Al10O35: Mn4+, Nd3+/Yb3+ materials can efficiently shift the short-wavelength sunlight in 250–550 nm spectral regions into near infrared emission which matches the higher sensitivity region of Si-based solar cells. The maximal energy transfer efficiency is 76.0% and 80.4% in Mn4+, Nd3+ and Mn4+, Yb3+ co-doped samples when excited at 460 nm, respectively. A dipole–dipole interaction is responsible for the energy transfer sensitization processes from Mn4+ to Nd3+/Yb3+ ions, which has been confirmed by Dexters theory and the Yokota–Tanimoto model.

Enhancement of 1.5 μm emission in Ce3+/Li+-codoped YPO4:Yb3+, Er3+ phosphor

YPO4:Yb3+, Er3+ near infrared luminescent materials have been prepared with a co-precipitation method. It is found that Ce3+, Li+ ions co-doped into the Y0.59Yb0.4Er0.01PO4 can result in the 1530 nm emission a 20 times of enhancement as compared with the Y0.58Yb0.4Er0.01Ce0.01PO4 counterpart, meaning it a promising phosphor of wide application prospects. The mechanism of the near infrared emission enhancement is ascribed to the high efficiency energy transfer from Er3+ to Ce3+ and the modification of the crystal field around Er3+ and Yb3+ ions caused by the doped Li+ ions.

CORRELATION BETWEEN THE ELASTIC AND THE VIBRONIC BEHAVIOR OF NANOSTRUCTURED TITANIA AND THEIR PRESSURE, SIZE, AND TEMPERATURE DEPENDENCE

Correlation between the elastic and the vibronic behavior of TiO2 and their responses to the variation of crystal size, applied pressure, and measuring temperature has been investigated based on the bond orderlength-strength correlation mechanism. Theoretical reproduction of the measurements claried that: (i) the elastic modulus (B) and the Raman shifts (� !) are strongly correlated and we can know either one of the B or the � ! from the other; (ii) the under- coordination induced cohesive energy loss and the energy density gain in the surface up to skin depth determines the size e®ect; (iii) bond expansion and bond weakening due to thermal vibration originates the thermally softened elastic modulus and the Raman shifts; and (iv) bond compression and bond strengthening results in the mechanically sti®ened elastic modulus and the Raman shifts. With the developed premise, one can predict the changing trends of the concerned properties with derivatives of quantitative information of the atomic cohesive energy, binding energy density, Debye temperature, and nonlinear compressibility of the specimen.

Some key factors affecting energy up-conversion efficiency of rare-earth doped oxy-fluoride materials

In this study, Er3+–Yb3+ co-doped oxy-fluoride glasses based on TeO2 have been investigated. Some approaches to enhancing up-conversion efficiency are presented. Generally, hosts with low phonon energy are beneficial to energy up-conversion. It is found that when the quasi-field-strength parameter \overlineM of the host is adjusted to approach that of the rare-earth dopant, the materials show high up-conversion efficiency. Selecting a suitable excitation photon energy to match the level of activated ions and/or sensitizing ions is a necessary condition for realizing high up-conversion efficiency. Our results offer some practical references for preparing rare-earth-doped energy up-conversion materials.