Article

Upconversion and Anti-Stokes Processes With f and d Ions in Solids

GOTR, UMR 7574-CNRS, 1, Place A-Briand, 92195 Meudon Cedex, France.
Chemical Reviews (Impact Factor: 46.57). 02/2004; 104(1):139-73. DOI: 10.1021/cr020357g
Source: PubMed

ABSTRACT

The anti-Stokes emissions or upconversion processes, for which emissions was found to exceed excitation energies by 10-100 kT, were presented. The dissolution of nanoparticles (6-8 nm) of Yb-Er- and Yb-Tm doped LuPO 4 as colloids in chloroform solutions was demonstrated. The Nd 3+-Yb3+ codoped YA nanocrystalline cemramics were also studied. It was observed that in thermoluminescence, where traps were emptied by excitation energies of the order of kT, constituted a field of anti-Stokes emission of its own.

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    • "Magnesium aluminum (MgAl 2 O 4 ) phosphor can show efficient luminescence in the presence of certain suitable dopants, particularly rare earths, in the lattice [5]. Phosphors, especially doped with erbium, are widely reported in the literature and have been used in visible up-conversion laser and efficient NIR lasers which could be used in the application of the display technologies, optical data storage and biomedical systems [6] [7]. "
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    ABSTRACT: Traditional and up-conversion luminescence of MgAl2O4 single crystal doped with erbium ions obtained by the Verneuil method has been investigated. The time resolved spectral measurements of the green and red up-conversion luminescence bands show that a build-up part is present in the up-conversion luminescence kinetics. This means that energy transfer process is involved in the creation of the luminescence. Considering rather small concentration of Er3+ in the material (0.12 mass %), the expected up-conversion mechanism should be excited state absorption since the average distance between erbium ions is high. The above-mentioned considerations suggest that clustering of the activator ions is present in the material, which is supported by SEM analysis.
    Full-text · Article · Dec 2015 · Physics Procedia
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    • "Then, one high energy photon is emitted. However, in Yb 3+ /Tb 3+ systems the cooperative sensitization mechanism is preferred [16] [24] . This mechanism occurs, when the emitter ion E has no energy level equal to half of the main emitting level. "
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    ABSTRACT: The presented study concerned up-converting core/shell type nanomaterials based on lanthanide(III) ions, Ln(III), doped orthoborates. The system studied composed of the GdBO3 doped with Yb3+/Tb3+ luminescent core ensured an effective cooperative sensitization up-conversion, resulting in a bright green luminescence. The silica coating process was performed by a modified Stöber method, which resulted in the formation of core-shell nanostructures, making them suitable for bioapplications. The nanophosphors and nanocomposites were obtained by various methods, such as co-precipitation in the presence of Triton X-100 and micelle synthesis with ethylenediaminetetraacetic acid (EDTA) as organic modifiers/surfactants. The synthesized nanomaterials were characterized with the use of powder X-ray diffraction (XRD), infrared light absorption with Fourier transform FT-IR spectra, transmission electron microscopy (TEM), up-conversion emission spectra under IR light, as well as excitation spectra, emission spectra and fluorescence lifetimes under UV light, and their photophysical properties were compared.
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    • "H 11/2 states, populated by more than two photon processes [44], contribute to the photocurrent of the silicon solar cell. Intense green luminescence due to the "
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    ABSTRACT: Up-conversion (UC) is a promising approach to utilize sub-band-gap photons for solar cells (SCs). Due to the non-linear nature of UC, the optimal excitation power regimes between the solar cell semiconductor and the UC material correspond to a difference in solar concentration of more than an order of magnitude. This difference can be bridged with integrated optics by concentrating the photons transmitted through the solar cell to increase the power density and maximize the intensity of UC luminescence. To realize this, dielectric-filled compound parabolic concentrators (CPCs) were used as integrated optics on the rear side of a planar bifacial silicon solar cell together with a 25% Er3+ doped hexagonal sodium yttrium fluoride (β-NaYF4:Er) UC phosphor. An efficiency increase of 32% from 0.123% to 0.163% under sub-band-gap illumination is quantified by means of the first ever reported I–V characteristics for an up-conversion solar cell (UC-SC) based on c-Si. An enhancement in external quantum efficiency (EQE) is obtained from 1.33% for the non-concentrating reference UC-SC to 1.80% for a solar cell with integrated optics for an excitation at 1523 nm with an irradiance of 0.024 W/cm2, corresponding to a normalized EQE of 0.75 W/cm2. This demonstrates that CPCs are suitable for UC-SC as they increase the concentration in the forwards direction, while maintaining high collection efficiency of the UC emission in the reverse direction. In addition, such an approach enables the optimization of the solar concentration on the UC phosphor independently from the concentration required for the solar cell.
    Full-text · Article · Jul 2015 · Solar Energy Materials and Solar Cells
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