Visible up-conversion is observed in the Ni 2+ , Er 3+ , Nb 5+ tri-doped Y 2 Mg 3 Ge 3 O 12 phosphor under excitation of light within its broad absorption band (900–1700 nm) such as 980 nm, 1064 nm, 1342 nm and 1550 nm.
Y2O3 with particle sizes ranging from 5 nm to 1 μm were studied at high pressure using x-ray diffraction and Raman spectroscopy techniques. Nanometer-sized Y2O3 particles are shown to be more stable than their bulk counterparts, and a grain size-dependent crystalline-amorphous transition was discovered in these materials. High-energy atomic pair distribution function measurements reveal that the amorphization is associated with the breakdown of the long-rang order of the YO6 octahedra, while the nearest-neighbor edge-shared octahedral linkages are preserved.
In this paper, we report the upconversion luminescence of Nd: fluoride glasses pumped with 858 nm diode laser. Among the observed upconversion spectra, the green emission concerning with three photon process has overwhelming superiority in intensity, when the doping concentration of Nd3+ is enhanced, the green upconversion emission increases more drastically than that of other upconverted emissions. The experiment results indicate that fluoride glasses doped with Nd3+ posssess possibility of being green emitting upconversion materials. When the upconversion mechanism is discussed, the green luminescence concerning with three-photon is ascribed to three-ion cooperative upconversion.
This study demonstrates a feasible and efficient route to alleviate the absorption problem of the terrestrial solar spectrum and enhance broadband luminescence from a promising down conversion powder phosphor YPO4 co-doped with Pr3+-Yb3+ lanthanide ion-couple: incorporating a third sensitizing transition metal ion, e.g., Ti4+. The x-ray powder diffraction results confirm the lattice substitution by the solid-state reaction doping rather than the formation of any secondary phase. The emission spectral results and the luminescence decay curve analysis show that the downconversion luminescence can be enhanced by 200%–300% and the quantum efficiency enhanced by more than 20% at the wavelength of around 980 nm, the best response spectrum for Si-based solar cells, by optimizing TiO2 doping concentration at 7 mol. %.
Under 980 nm excitation, we obtained five intense up-conversion luminescence bands in Er 3+-Yb 3+-Tm 3+co-doped CdF 2:PbF 2-based glass as follows: infrared(800 nm), red(645 nm), green (545 nm and 525 nm), blue(480 nm ) and violet(407 nm) up-conversion luminescence. With the addition of Tm 3+, the intensity of 480 nm blue luminescence increased notably compared with that of co-doped Yb 3+-Er 3+ sample, which attributed to Tm 3+ special energy level structure; logI-logP plot of the luminescence intensity versus pump power shows that 480 nm luminescence emission is a two-photon excitation process induced by the cooperative up-conversion between two Yb 3+ ions and the slope of logI-logP plot decreases gradually with increasing pump power and shows a tendency to bend down. The up-conversion mechanism is analyzed in detail under 980 nm semiconductor laser excitation; the dependence of 480 nm up-conversion luminescence intensity on the pump power under the steady states is discussed by using rate equation and the results agree well with the experiments.
Li+-doped HoPO4 powders with a pure tetragonal phase are successfully synthesized by the co-precipitation method. It exhibits an obvious color change under sunlight and tri-phosphor fluorescent light illumination. The introduction of Li+ ions into HoPO4 can further enhance its photochromic property effectively. The doped Li+ ions induce changes in the crystal structure. The spectral characteristics and thus photochromic properties of HoPO4 are explored. The improved HoPO4 powder, when used as a photochromic material, has wide-ranging prospects in security, decoration, and other applications.
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