Abstract: We systematically studied the photoconductivity of nominally intrinsic diamond films grown by two CVD methods. In the 200–275 nm wavelength range covering the bandgap energy (5.5 eV or 225 nm), the measured photocurrent showed characteristic behavior that can be quantitatively related to a fast recombination of electrons and effective trapping of holes, mainly by trap states near the valence band edge. In addition to photoconductivity, thermoelectric emission spectroscopy and thermally stimulated current measurements were made. From the results, the density and location of two distinctive trap levels within the energy bandgap was estimated. The results are not only self-consistent, but also agree with other authors' findings, such as a hole-dominated current, without or under bandgap illumination, a Fermi level close to the valence band edge, an electron recombination center in the middle of the bandgap, and a shallow hole-trap state having an extremely high density of ∼ 1019 cm−3. Based on these data, we suggest a bandgap and trap-state model for intrinsic CVD diamond. The details of this model and the characteristic properties of the defects/traps are consistent with experimental results and theoretical findings made by other authors covering a large diversity of areas, such as photoluminescence and cathodoluminescence, photoabsorption, carrier lifetimes and mobilities, electron paramagnetic resonance, cold-cathode electron emission, and photoconductive current switching.
E.-K.Souw, R.J. Meilunas, C.Szeles, N.M.Ravindra, F.-M.Tong

Abstract: A panchromatic specular reflector based dye solar cell is presented herein. Photovoltaic performance of this novel design is compared to that of cells in which standard diffuse scattering layers are integrated. The capability of the proposed multilayer structures to both emulate the broad band reflection of diffuse scattering layers of standard thickness (around 5 microns) and give rise to similarly high light harvesting and power conversion efficiencies, yet preserving the transparency of the device, is demonstrated. Such white light reflectors are comprised of stacks of different porous optical multilayers, each one displaying a strong reflection in a complementary spectral range, and are designed to leave transmittance unaltered in a narrow red-frequency range in which the sensitized electrode shows negligible absorption, thus allowing us to see through the cell. The reflectance bandwidth achieved is three times as broad as the largest bandwidth previously achieved using any photonic structure integrated into a dye solar cell.
Carmen López-López , Silvia Colodrero and Hernán Míguez

Abstract: Herein we report an experimental analysis of the performance of photonic crystal based dye solar cells (PC-DSCs) as the incident light angle moves away from the normal with respect to the cell surface. Nanoparticle multilayers operating at different wavelength ranges were coupled to the working electrode of a dye solar cell for this study. The interplay between optical and photovoltaic properties with the incident light angle is discussed. We demonstrate that an efficiency enhancement is attained for PC-DSCs at all angles measured, and that rational design of the photonic crystal back mirror leads to a reduction of the photocurrent losses related to the tilt angle of the cell, usually labeled as cosine losses. Angular variations of the cell transparency are also reported and discussed. These angular properties are relevant to the application of these solar devices in building integrated photovoltaics as potential window modules.
Carmen López-López , Silvia Colodrero , Mauricio E. Calvo and Hernán Míguez

Abstract: Porous silicon samples have been prepared from p-type single-crystal silicon 〈100〉 by a galvanostatic and an open-circuit etch in 50% HF. The materials display bright red-orange room-temperature photoluminescence (PL) in air and toluene solution. Infrared measurements show that the porous silicon surface is partially oxidized. Exposure to anthracene (An) or 10-methylphenothiazine (MPTZ) results in dynamic quenching of the material's excited state(s). Nanosecond time-resolved PL decays are complex and wavelength dependent, with average lifetimes in neat toluene of 0.3−16 μs. Quenching by An and MPTZ is more efficient and rapid at short observation wavelengths. The steady-state and time-resolved quenching data are well fit to the Stern−Volmer model. The PL decays are well described by a skewed distribution of recombination rates.
Minh C. Ko and Gerald J. Meyer

Abstract: Cation channelrhodopsins, light-gated channels from flagellate green algae, are extensively used as optogenetic photoactivators of neurons in research and recently have progressed to clinical trials for vision restoration. However, the molecular mechanisms of their photoactivation remain poorly understood. We recently identified cryptophyte cation channelrhodopsins, structurally different from those of green algae, which have separately evolved to converge on light-gated cation conductance. This study reveals diversity within this new protein family and describes a subclade with unusually rapid desensitization that results in short transient photocurrents in continuous light. Such transient currents have not been observed in the green algae channelrhodopsins and are potentially useful in optogenetic protocols. Kinetic UV-visible (UV-vis) spectroscopy and photoelectrophysiology reveal that the desensitization is caused by rapid accumulation of a nonconductive photointermediate in the photochemical reaction cycle. The absorption maximum of the intermediate is 330 nm, the shortest wavelength reported in any rhodopsin, indicating a novel chromophore structure. ABSTRACT Channelrhodopsins guide algal phototaxis and are widely used as optogenetic probes for control of membrane potential with light. “Bacteriorhodopsin-like” cation channelrhodopsins (BCCRs) from cryptophytes differ in primary structure from other CCRs, lacking usual residues important for their cation conductance. Instead, the sequences of BCCR match more closely those of rhodopsin proton pumps, containing residues responsible for critical proton transfer reactions. We report 19 new BCCRs which, together with the earlier 6 known members of this family, form three branches (subfamilies) of a phylogenetic tree. Here, we show that the conductance mechanisms in two subfamilies differ with respect to involvement of the homolog of the proton donor in rhodopsin pumps. Two BCCRs from the genus Rhodomonas generate photocurrents that rapidly desensitize under continuous illumination. Using a combination of patch clamp electrophysiology, absorption, Raman spectroscopy, and flash photolysis, we found that the desensitization is due to rapid accumulation of a long-lived nonconducting intermediate of the photocycle with unusually blue-shifted absorption with a maximum at 330 nm. These observations reveal diversity within the BCCR family and contribute to deeper understanding of their independently evolved cation channel function. IMPORTANCE Cation channelrhodopsins, light-gated channels from flagellate green algae, are extensively used as optogenetic photoactivators of neurons in research and recently have progressed to clinical trials for vision restoration. However, the molecular mechanisms of their photoactivation remain poorly understood. We recently identified cryptophyte cation channelrhodopsins, structurally different from those of green algae, which have separately evolved to converge on light-gated cation conductance. This study reveals diversity within this new protein family and describes a subclade with unusually rapid desensitization that results in short transient photocurrents in continuous light. Such transient currents have not been observed in the green algae channelrhodopsins and are potentially useful in optogenetic protocols. Kinetic UV-visible (UV-vis) spectroscopy and photoelectrophysiology reveal that the desensitization is caused by rapid accumulation of a nonconductive photointermediate in the photochemical reaction cycle. The absorption maximum of the intermediate is 330 nm, the shortest wavelength reported in any rhodopsin, indicating a novel chromophore structure
O. Sineshchekov, E. Govorunova, Hai Li, Yumei Wang, M. Melkonian, G. K. Wong, L. Brown, J. Spudich

Abstract: Herein is presented what is believed to be the first example of integration of photonic structures in a flexible optoelectronic device. The resulting devices may be designed to display any color in the visible range and, simultaneously, present enhanced power conversion efficiency as a consequence of the increased light harvesting caused by the colored back reflection. The achievement results from the incorporation of nanoparticle‐based multilayers with photonic crystal properties that are modified to be compatible with the chemical and physical processing of flexible nanocrystalline titania electrodes of dye solar cells. The photovoltaic performance of these colored flexible cells remains unaltered after one hundred bending cycles, thus showing the high‐mechanical stability of the ensemble. These devices reunite most characteristics required for building integration or for the construction of solar window panes, such as light weight, stability upon bending, adaptability, and color. This work may trigger promising applications of these highly adaptable and versatile photonic crystals in other flexible devices.
Yuelong Li, Mauricio E. Calvo, Hernán Míguez

Abstract: Rhodopsin photosensors of phototactic algae act as light-gated cation channels when expressed in animal cells. These proteins (channelrhodopsins) are extensively used for millisecond scale photocontrol of cellular functions (optogenetics). We report characterization of PsChR, one of the phototaxis receptors in the alga Platymonas (Tetraselmis) subcordiformis. PsChR exhibited ∼3-fold higher unitary conductance and greater relative permeability for Na+ ions, as compared with the most frequently used channelrhodopsin-2 from Chlamydomonas reinhardtii (CrChR2). Photocurrents generated by PsChR in HEK293 cells showed lesser inactivation and faster peak recovery than those by CrChR2. Their maximal spectral sensitivity was at 445 nm, making PsChR the most blue-shifted channelrhodopsin so far identified. The λmax of detergent-purified PsChR was 437 nm at neutral pH and exhibited red shifts (pKa values at 6.6 and 3.8) upon acidification. The purified pigment undergoes a photocycle with a prominent red-shifted intermediate whose formation and decay kinetics match the kinetics of channel opening and closing. The rise and decay of an M-like intermediate prior to formation of this putative conductive state were faster than in CrChR2. PsChR mediated sufficient light-induced membrane depolarization in cultured hippocampal neurons to trigger reliable repetitive spiking at the upper threshold frequency of the neurons. At low frequencies spiking probability decreases less with PsChR than with CrChR2 because of the faster recovery of the former. Its blue-shifted absorption enables optogenetics at wavelengths even below 400 nm. A combination of characteristics makes PsChR important for further research on structure-function relationships in ChRs and potentially useful for optogenetics, especially for combinatorial applications when short wavelength excitation is required. [Link]
Elena G. Govorunova, Oleg A. Sineshchekov, Hai Li, Roger Janz and John L. Spudich

Abstract: The application of UV photoacoustic spectroscopy to the evaluation of UV-absorbing paint additives in clear paint layers is described. This technique enables the quantitative analysis of additive concentration and aids in determining the effects due to paint processes and substrate composition changes on additive concentration. The inclusion of photoacoustic phase information is essential to offset the saturation effects that dominate these strongly absorbing samples. Two analysis techniques are evaluated, both of which partially or totally utilize the phase data. When comparisons between samples on substrates with different heat capacities are needed, the phase-only method is preferred. Otherwise, the two methods give comparable results. Using these methods, two different paint/substrate/additive systems are easily evaluated for changes in process or changes in substrate materials. The instrumentation and interpretation methods are discussed in detail.
Roscoe O. Carter, III

Abstract: Herein we analyze experimentally the effect that introducing highly reflecting photonic crystals, operating at different spectral ranges, has on the conversion efficiency of dye sensitized solar cells. The interplay between structural colour and cell performance is discussed on the basis of the modified spectral response of the photogenerated current observed and the optical characterization of the cells. We demonstrate that, with the approach herein discussed, it is possible to achieve relatively high efficiencies using thin electrodes while preserving transparency. At the same time, the appearance of the device can be controllably modified, which is of relevance for their potential application in building integrated photovoltaics (BIPV) as window modules.
Daniele Colonna,a Silvia Colodrero,b Henrik Lindström,c Aldo Di Carloa and Hernán Míguez*b

Abstract: A two-compartment photoelectrochemical cell consisting of a CdS photoanode immersed in aqueous sulfide solution, Nafion membrane, platinum cathode and sulfuric acid solution as the dark-compartment electrolyte was constructed. The effects of the concentrations of the electrolytes, membrane surface and cathode materials on the performance of the cell were studied to reach high quantum yield of hydrogen production. Under optimized conditions, light to hydrogen conversion efficiency up to 12% was observed under sun light illumination.
Grzegorz Milczareka, Atsuo Kasuyab, Sergiy Mamykinb, T. Araib, K. Shinodab, K. Tohjib

Abstract: Photoacoustic Spectroscopy (PAS) experiments in the visible and ultraviolet regions of the electromagnetic spectrum were carried out on a variety of tourmaline species. The results of our investigation show that PAS can be seen as a powerful alternative spectroscopic tool in the identification and characterization of color centers in mineral specimens.
R.J.S. Lima1, A.S. Vasconcelos1, R.R. Wegner2 and J.F. Suassuna1

Abstract: Composite structures of Ru(bpy)2(4,4′-(PO3H2)2bpy)2+ surface bound to nanocrystalline TiO2 with an overlayer of Ru(bpy)32+ ion exchanged into Nafion, FTO|nanoTiO2-[Ru(bpy)2(4,4′-(PO3H2)2bpy)]2+/Nafion,Ru(bpy)32+ (FTO = fluorine-doped tin oxide), have been prepared and characterized. Steady-state emission and time-resolved lifetime measurements demonstrate that energy transfer occurs from Nafion,Ru(bpy)32+* to adsorbed Ru(bpy)2(4,4′-(PO3H2)2bpy)2+ with an efficiency of ∼0.49. Energy transfer sensitizes photoinjection by the adsorbed metal-to-ligand charge transfer (MLCT) excited state by an “antenna effect.”
Paul G. Hoertz ‡, Anna Goldstein , Carrie Donley §, and Thomas J. Meyer

Abstract: Porous silicon samples have been prepared from p-type single-crystal silicon 〈100〉 by a galvanostatic and an open-circuit etch in 50% HF. The materials display bright red-orange room-temperature photoluminescence (PL) in air and toluene solution. Infrared measurements show that the porous silicon surface is partially oxidized. Exposure to anthracene (An) or 10-methylphenothiazine (MPTZ) results in dynamic quenching of the material's excited state(s). Nanosecond time-resolved PL decays are complex and wavelength dependent, with average lifetimes in neat toluene of 0.3−16 μs. Quenching by An and MPTZ is more efficient and rapid at short observation wavelengths. The steady-state and time-resolved quenching data are well fit to the Stern−Volmer model. The PL decays are well described by a skewed distribution of recombination rates.
Minh C. Ko and Gerald J. Meyer