Phase evolution of KLaF4 nanocrystals and their effects on the photoluminescence of Nd3+ doped transparent oxyfluoride glass-ceramics

Quantity of cubic (α-phase) and hexagonal (β-phase) KLaF₄ nanocrystals (NCs) tailored by doping.

Oxyfluoride glass–ceramic fibers doped with Nd3+: structural and optical characterization

Selective excitation in an oxyfluoride glass–ceramic optical fiber containing LaF₃ nanocrystals doped with Nd³⁺.

Luminescence and structural analysis of Ce3+ and Er3+ doped and Ce3+–Er3+ codoped Ca3Sc2Si3O12 garnets: influence of the doping concentration in the energy transfer processes

We present a structural a spectroscopy analysis of Ca₃Sc₂Si₃O₁₂ garnets doped with Ce³⁺ and Er³⁺ ions that were synthesized by the freeze-drying precursor method. Efficient energy transfer has been obtained result in an enhanced NIR emission.

Energy level diagram and kinetics of luminescence of Ag nanoclusters dispersed in a glass host

A site-selective spectroscopy study of Ag nanoclusters dispersed in oxyfluoride glass hosts has been carried out. The nano- to millisecond, essentially non-exponential, luminescence kinetics of Ag nanoclusters has been detected in the spectral range from 450 to 1000 nm, when excited at discrete wavelengths in the range 250 to 450 nm. Based on these experimental observations, the energy level configuration coordinate diagram for the involved ground and excited singlet/triplet states of the Ag nanoclusters has been proposed and confirmed by the density functional theory (DFT). The sites for the Ag nanoclusters are argued to be multiple. The structure/geometry of the involved Ag nanoclusters has been suggested to involve spin-paired dimers Ag²⁺, or tetramers Ag₄²⁺, with a varying elongation/distortion along the tetramer diagonals.

Site-selective spectroscopy in Sm(3+)-doped sol-gel-derived nano-glass-ceramics containing SnO(2) quantum dots

Nano-glass-ceramics of composition 95SiO(2)-5SnO(2) doped with 0.4 Sm(3+) (mol%) were synthesized by the thermal treatment of precursor sol-gel glasses. Structural and luminescence measurements were carried out. The precipitated SnO(2) nanocrystals in the glass matrix constitute a wide bandgap quantum-dot system with size comparable to the bulk exciton Bohr radius. A site-selective excitation, by energy transfer from the semiconductor host, reveals that a fraction of the Sm(3+) ions are incorporated in the SnO(2) nanocrystals, whereas the rest remains in the silica glassy phase. An evolution in the Sm(3+) emission spectra has been observed when the SnO(2) nanocrystals are excited with different UV wavelengths, which has been ascribed to selective excitation of nanocrystal sets with predetermined size.

Chemotactic collapse for the Keller-Segel model

This work is concerned with the system (equation: see text), where Gamma, chi are positive constants and Omega is a bounded and smooth open set in IR2. On the boundary delta Omega, we impose no-flux conditions: (equation: see text). Problem (S), (N) is a classical model to describe chemotaxis corresponding to a species of concentration u(x,t) which tends to aggregate towards high concentrations of a chemical that the species releases. When completed with suitable initial values at t = 0 for u(x,t), v(x,t), the problem under consideration is known to be well posed, locally in time. By means of matched asymptotic expansions techniques, we show here that there exist radial solutions exhibiting chemotactic collapse. By this we mean that u(r,t) --> A delta (y) as t --> T for some T < infinity, where A is the total concentration of the species.