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  • 1
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    Polymer based whispering gallery mode laser for biosensing applications (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-01-21
    Description: Whispering gallery mode lasers are of interest for a wide range of applications and especially biological sensing, exploiting the dependence of the resonance wavelengths on the surrounding refractive index. Upon lasing, the Q factors of the resonances are greatly improved, enabling measurements of wavelength shifts with increased accuracy. A way forward to improve the performance of the refractive index sensing mechanism is to reduce the size of the optical resonator, as the refractive index sensitivity is inversely proportional to the resonator dimensions. However, as the lasing threshold is believed to depend on the Q factor among other parameters, and the reduction of the microresonator size results in lower Q, this poses additional challenges for reaching the lasing threshold. In this letter, we demonstrate lasing in 10  μ m diameter dye doped polystyrene microspheres in aqueous solution, the smallest polystyrene microsphere lasers ever reported in these conditions. We also investigate the dependence of the lasing threshold on the Q factor by changing the refractive index surrounding the sphere, highlighting a much stronger dependency than initially reported.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    Temperature dependence of hydrogenated amorphous silicon solar cell performances (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-01-28
    Description: Thin-film hydrogenated amorphous silicon solar ( a -Si:H) cells are known to have better temperature coefficients than crystalline silicon cells. To investigate whether a -Si:H cells that are optimized for standard conditions (STC) also have the highest energy yield, we measured the temperature and irradiance dependence of the maximum power output ( P mpp ), the fill factor ( FF ), the short-circuit current density ( J sc ), and the open-circuit voltage ( V oc ) for four series of cells fabricated with different deposition conditions. The parameters varied during plasma-enhanced chemical vapor deposition (PE-CVD) were the power and frequency of the PE-CVD generator, the hydrogen-to-silane dilution during deposition of the intrinsic absorber layer ( i -layer), and the thicknesses of the a -Si:H i -layer and p -type hydrogenated amorphous silicon carbide layer. The results show that the temperature coefficient of the V oc generally varies linearly with the V oc value. The J sc increases linearly with temperature mainly due to temperature-induced bandgap reduction and reduced recombination. The FF temperature dependence is not linear and reaches a maximum at temperatures between 15 °C and 80 °C. Numerical simulations show that this behavior is due to a more positive space-charge induced by the photogenerated holes in the p -layer and to a recombination decrease with temperature. Due to the FF ( T ) behavior, the P mpp ( T ) curves also have a maximum, but at a lower temperature. Moreover, for most series, the cells with the highest power output at STC also have the best energy yield. However, the P mpp ( T ) curves of two cells with different i -layer thicknesses cross each other in the operating cell temperature range, indicating that the cell with the highest power output could, for instance, have a lower energy yield than the other cell. A simple energy-yield simulation for the light-soaked and annealed states shows that for Neuchâtel (Switzerland) the best cell at STC also has the best energy yield. However, for a different climate or cell configuration, this may not be true.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 3
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    Light-induced Voc increase and decrease in high-efficiency amorphous silicon solar cells (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-09-05
    Description: High-efficiency amorphous silicon ( a -Si:H) solar cells were deposited with different thicknesses of the p -type amorphous silicon carbide layer on substrates of varying roughness. We observed a light-induced open-circuit voltage ( V oc ) increase upon light soaking for thin p-layers, but a decrease for thick p-layers. Further, the V oc increase is enhanced with increasing substrate roughness. After correction of the p -layer thickness for the increased surface area of rough substrates, we can exclude varying the effective p -layer thickness as the cause of the substrate roughness dependence. Instead, we explain the observations by an increase of the dangling-bond density in both the p -layer—causing a V oc increase—and in the intrinsic absorber layer, causing a V oc decrease. We present a mechanism for the light-induced increase and decrease, justified by the investigation of light-induced changes of the p -layer and supported by Advanced Semiconductor Analysis simulation. We conclude that a shift of the electron quasi-Fermi level towards the conduction band is the reason for the observed V oc enhancements, and poor amorphous silicon quality on rough substrates enhances this effect.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of high pressure on the exchange interactions in binuclear chromium (III) complexes (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 3166-3172 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Single crystals of [LCr(III) (OH)3Cr(III)L](ClO4)3 (L=1,4,7-trimethyl-1,4,7-triazacyclononane) and [(NH3)5Cr(III)OHCr(III)(NH3)5]Cl5⋅H2O were studied by low-temperature luminescence spectroscopy under hydrostatic pressure up to 42 kbar. Dramatic shifts of the sharp luminescence lines up to 300 cm−1 were observed. The ground state exchange parameters ||J|| were found to increase linearly with pressure by d||J||/dP=0.7 and 0.15 cm−1/kbar, respectively. Using the shift of the 4A2→4T2 absorption bands as a function of the applied pressure the local compressibilities were estimated. The increase of ||J|| with decreasing interatomic distances was rationalized by extended Hückel calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453056
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  • 5
    Electronic Resource
    Electronic Resource
    Low-cost apparatus for high-pressure optical spectroscopy at low temperatures (1987)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 58 (1987), S. 1122-1123 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A high-pressure cell with sapphires as Bridgman anvils and a simple flow tube cryostat for optical spectroscopy are described. Temperatures down to 10 K and pressures up to 50 kbar are easily obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139568
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  • 6
    Electronic Resource
    Electronic Resource
    Luminescence and excitation line narrowing of [Ru(2,2'-bipyridine)3−x (2,2'-bipyridine-d8)x]2+ (x=0–3) in [Zn(2,2'-bipyridine)3](CIO4)2. Unequivocal evidence for localized lowest-excited states (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 7614-7618 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Broadband and narrowed luminescence and excitation spectra at liquid helium temperatures of the title series (abbreviated as h24, d8, d16, and d24 for x=0, 1, 2, and 3, respectively) are reported. The luminescence spectra of the h24, d8, and d24 materials are found to be very similar except that the inhomogeneous broadening varies and a deuteration shift of 37 cm−1 to higher energy is observed for the d24 system. The luminescence of the d16 material is a superposition of the h24 and d24 spectra. Two distinct luminescence lifetimes can be measured in this material. The excitation spectra of the d8 and d16 materials are well represented as superpositions of the h24 and d24 spectra. The crystal structure establishes that there is only one spectroscopic site with two equivalent ligands. The third ligand has a different environment. The lowest-excited metal-to-ligand charge transfer states of the two equivalent ligands are localized on an electronic time scale but very fast intramolecular excitation energy transfer occurs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465691
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  • 7
    Electronic Resource
    Electronic Resource
    Persistent spectral hole-burning, luminescence line narrowing and selective excitation spectroscopy of the R lines of Cr(III) tris(2,2'-bipyridine) in amorphous hosts (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 7902-7910 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The distributions of the 2E and the 4A2 splittings of Cr(III) tris(2,2'-bipyridine) embedded in a wide range of amorphous hosts are investigated by means of luminescence line narrowing and hole-burning spectroscopies. A large spread of the 2E splitting is observed for all amorphous matrices and this is attributed mainly to low symmetry field contributions. A simple model is proposed which rationalizes the observed non-Gaussian distribution of R2 energies as a function of the selected R1 energy. The zero field splitting of the 4A2 ground state also shows a significant variation in all the investigated samples. An important conclusion is that optically detected magnetic resonance and electron paramagnetic resonance measurements of transition metal complexes in amorphous hosts need to be interpreted with care. The homogeneous linewidth of the R1 line was measured at 1.5 K for five hosts and ranged from 80 MHz in glycerol to 460 MHz in 4:1 ethanol/methanol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463465
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  • 8
    Electronic Resource
    Electronic Resource
    Luminescence and excitation spectroscopy of ruthenocene (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 4131-4135 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The luminescence and excitation spectra of the perdeuterated and the protonated ruthenocene have been carefully investigated. The electronic origins are at 21 459 cm−1 and at 21 390 cm−1 for the perdeuterated and protonated crystals, respectively. The two observed luminescence progressions in the metal-ring stretch a'1 (D5h notation) in the perdeuterated crystal are separated by 155 cm−1 compared to the 165–170 cm−1 reported for the protonated compound. The metal-ring stretch frequency is reduced to 318 cm−1 in the perdeuterated crystal from the 333 cm−1 found for the protonated compound. In both crystals the observed doubling of the vibrational progression is due to a false origin based on a skeletal bending mode δ(ring-Ru-ring) which transforms as e1 in D5h. This mode is split by 7–8 cm−1 via the low site symmetry (Cs) in the crystal. The excitation spectrum of both compounds shows only a single progression in the metal-ring stretch. This frequency is reduced by 16% in the excited state for both the protonated and the perdeuterated crystal. Deuteration increases the lifetime from 127 μs to 990 μs at 1.5 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461868
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  • 9
    Electronic Resource
    Electronic Resource
    Site-selective and Stark spectroscopy of the series [Os(2,2'-bipyridine)3−x(2,2'-bipyridine-d8)x]2+ (x=0–3) in single-crystal [Ru(2,2'-bipyridine)3](PF6)2. Localization of an intramolecular triplet metal-to-ligand charge transfer exciton by partial deuteration (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 4823-4831 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Selective luminescence and excitation spectroscopy and Stark experiments of the title systems are reported. Dramatic differences of the x=1 and x=2 spectra, in comparison with the x=0 and x=3 spectra are observed. The lowest-excited state in the x=1 and x=2 spectra is a charge-transfer excitation localized on the protonated ligand(s). A superposition of "deuterated'' and "protonated'' transitions is observed for the x=1 and x=2 systems in the excitation spectra. The deuteration shift (≈32 cm−1) is much larger than the excitation exchange interaction β between the metal–ligand subunits. ||β|| is ≈2 cm−1, as directly determined from the observed splittings (5–7 cm−1) of I, the lowest-energy electronic origin. Stark shifts confirm the charge transfer character of the lowest-excited states. The splittings and relative intensities of the origins and their Stark effect can be quantitatively described by an exciton formalism. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469530
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