Search

1,2-dichloroethane (${{\rm C}_2}{{\rm H}_4}{{\rm Cl}_2}$) and 1,2-dibromoethane (${{\rm C}_2}{{\rm H}_4}{{\rm Br}_2}$) show linear absorption (LA) and stimulated light scattering in response to the excitation by 820 nm 18 fs laser pulses. Using the $Z$-scan technique, with these pulses separated by 12.2 ns (much shorter than both samples’ thermal diffusivity time constants ${\tau _{\rm th}}$’s) and extended over 41 ms (considerably longer than ${\tau _{\rm th}}$’s), we investigated the thermal lensing effect of both samples and found that LA dominates their heating. In addition, relative to ${{\rm C}_2}{{\rm H}_4}{{\rm Br}_2}$, ${{\rm C}_2}{{\rm H}_4}{{\rm Cl}_2}$ shows more/less thermal lensing effect before/after the exposure time passes ${\tau _{\rm th}}$’s. This means that the thermal lensing effect is more severely reinforced by heating and stabilized by thermal diffusivity in ${{\rm C}_2}{{\rm H}_4}{{\rm Cl}_2}$ than in ${{\rm C}_2}{{\rm H}_4}{{\rm Br}_2}$. Notably, the Kerr lensing effect is negligible in this study, although it is noticeable in a $Z$-scan study with 17 ps laser pulses.

We have established a thermal distribution model of the multilayer dielectric grating with laser irradiation based on the Beer–Lambert theory and the thermal conduction theory. The temperature change on the surface and inside of the grating is simulated according to the laser irradiation time, laser power, substrate size, and substrate material. The actual thermal behavior of a 50 × 50 × 10 mm3 multilayer dielectric grating with fused silica substrate is measured with 10 kW fiber laser irradiation. The results show a dynamic equilibrium between the energy absorbed in the laser irradiation area and the energy transferred in the thermal transfer area when the maximum temperature of the grating is kept stable. The simulation results are in good agreement with the experimental data, which provides a reference for understanding the thermal dynamics process of the multilayer dielectric grating with high power density laser irradiation.

Using the Z-scan technique with 532 nm 19 ps laser pulses separated by two time intervals τ

The aim of this work is to clarify the mechanism of photo-absorption-caused solute migration at the microscopic level. Experimentally, we respectively measured the short-pulse-induced and continuous-light-driven migrations of chloroaluminum phthalocyanine molecules dissolved in ethanol at two concentrations, 4.2 × 1017 cm−3 (7.0 × 10−4 M) and 1.2 × 1017 cm−3 (2.0 × 10−4 M). Theoretically, by verifying that individual solute molecules in the concentrated solution, compared to those in the dilute solution, absorb more photo energy collectively but less photo energy individually, we consider solute migration as net movement of individual solute molecules and then sequentially analyse how individual solute molecules absorb photo energy, convert the absorbed photo energy into translational excess energy intra-molecularly and carry out movement. Subsequently, by summing up movement of individual solute molecules in a unit of volume, we deduce the solute migration behaviours which coincide with the experimental results: for short pulse excitation, solute migration is more/less in the concentrated solution depending on the pulse energy; for continuous light irradiation, solute migration is always more in the concentrated solution regardless of the light power. Note that, in our theoretical deduction, the short-pulse-induced and continuous-light-driven solute migrations differ in that the former proceeds before inter-molecular relaxation becomes apparent and the latter carries on with inter-molecular relaxation practiced sufficiently. Accordingly, the former is non-quasistatic and the latter is quasistatic and thus referred to as thermal diffusion.

Novel and less toxic quantum dot (QD) semiconductors are desired for developing environmentally benign colloidal quantum dot solar cells. Here, the synthesis of novel lead/cadmium-free neodymium chalcogenide Nd2(S, Se, Te)3 QDs via solution-processed method is reported for the first time. The results show that small-bandgap semiconductor QDs with a narrow size distribution ranging from 2 to 8 nm can be produced, and the wide absorption band can be achieved by the redshift owing to the size quantization effect by controlling the initial loading of chalcogenide precursors. By analyzing the band structure of QDs and the energy level alignment between QDs and TiO2, the influence of energy offset between the conduction band edges of QDs and TiO2 on the charge transfer dynamics and photovoltaic performance of QD solar cells (QDSCs) is investigated. It is revealed that among the three types of QDs studied, Nd2Se3 QDSCs with the smallest energy offset exhibit the best performances and a decent power conversion efficiency of 3.19% is achieved. This work clearly demonstrates the promising potentials of novel rare earth chalcogenide quantum dots in photovoltaic applications.

A novel sandwich-type erbium triple-decker complexes with mixed phthalocyanine and Schiff-base ligands was synthesized and characterized by optical absorption spectroscopy. The third-order nonlinear optical properties of the sandwich-type complexes in dichloromethane were investigated using Z-scan measurement at 532 nm with 20 ps pulses. The Z-scan results reveal that the sandwich-type complexes exhibit strong reverse saturable absorption and self-focusing effect. The third-order nonlinear susceptibility and second-order hyperpolarizability of the complexes are estimated to be 7.31 × 10−13 esu and 0.94 × 10−30 esu, respectively. Our results indicate that the sandwich-type mixed (phthalocyaninato)(Schiff-base) complexes are promising candidate materials for future nonlinear optical applications such as wavelength conversion and optical switching.

A facile, low-cost and low-temperature fabrication approach of counter electrode is essential for pursuing robust photovoltaic devices. Herein, we develop a hydrothermal in situ growth of Cobalt–Ruthenium (Co–Ru) alloy nanofiber electrode for quantum dot solar cell (QDSC) applications. Colloidal CdS QDs with tunable absorption band edge are synthesized and used as light absorber. After optimizing the QDs with the highest photoluminescence quantum yield accompanied by considerable solar light absorption ability, QDSC based on Co–Ru alloy electrode delivers a much higher power conversion efficiency than its counterparts, i.e., either pure Co or Ru metal electrodes. In detail, Co–Ru alloy electrode exhibits high specific area, excellent electrical behavior, intimate interface contact, and good stability, thus leading to notable improved device performances. The impressive robust function of Co–Ru alloy with simple manufacturing procedure highlights its potential applications in robust QDSCs.

Metal oxide nanocrystals have been pursued for various applications in photovoltaics as a buffer layer. However, it remains a challenging task to adjust their energy levels to achieve a better match of the donor–acceptor system. Herein, we report the fabrication of graphene quantum dots (GQDs) with bright blue photoluminescence by a top-down strategy based on laser fragmentation with posthydrothermal treatment. The GQDs demonstrate appropriate energy level positions and are used as an intermediate buffer layer between TiO2 and P3HT to form a cascade energy level architecture. The introduction of the GQDs into a bulk heterojunction hybrid solar cell has led to an enhancement of the power conversion efficiency.

The photoexcited electron transfer rate represents one of the most important properties required for photovoltaic devices. However, the fabrication of solar cells with a faster electron transfer remains a technological challenge. Regulating the energy level alignment of acceptor-donor system by the incorporation of foreign ions is one of the most promising strategies to achieve this aim. Herein we demonstrate that the incorporation of silver ions into TiO2 nanocrystals results in a remarkable reduction of energy offset between the conduction band edge of acceptor and the lowest unoccupied molecular orbital of donor. In particular, the electron transfer life time was shortened from 30.2 to 18.3 ps, i.e., almost 40% faster than pure TiO2 acceptor, thus leading to a notable enhancement of power conversion efficiency by almost 38% in organic/inorganic hybrid solar cells. The reduction of the ‘excess’ energy offset accelerates the electron transfer, which is expected to have an important role in applications of solar energy conversion and photon detectors.

An effective energy level regulation of acceptor by doping samarium phosphate nanophosphors (SmPO4 NPs) was reported for inorganic/organic hybrid solar cell applications. SmPO4 NPs doped TiO2/P3HT bulk heterojunction (BHJ) solar cell shows an enhanced power conversion efficiency of approaching 3% as compared with that of its counterpart without SmPO4 NPs (1.98%). The underlying photophysical mechanism was probed by applying femtosecond transient absorption spectroscopy and the results show that the efficiency enhancement was ascribed to the improved hot electron, less energetic electron, hole transports at the interface of BHJ apart from down-conversion photoluminescence of SmPO4 NPs. It has been evidenced that the hot electron transfer life time was shortened by more than 40% (i.e., from τhot-e=30.2 to 17.9 ps) than pure TiO2 acceptor while the hole transfer lifetime was boosted by almost 20% (i.e., from 6.92 to 5.58 ns). Such charge carrier improvements stem from the efficient energy level regulations by SmPO4 NPs. In detail, the conduction band (CB) edge of TiO2 has been elevated by 0.57 eV while the valence band (VB) edge has been elevated by 0.32 eV, thus not only narrowing down the energy offset between CB energy levels of acceptor TiO2 and donor P3HT, but also meanwhile enlarging the band gap of TiO2 itself that permits to inhibit electron-hole recombination within TiO2. This work demonstrates that samarium ions can efficiently facilitate exciton generation, dissociation and charge transport and have an important role in enhancing photovoltaic performance.

Photovoltaic performances are critically dependent on efficient photoexcited charge carrier generation. Vanadium ions are introduced into titanium dioxide (TiO2) as a photocatalyst to tailor the energy level alignment of TiO2 and the conjugated polymer poly(3-hexylthiophene) (P3HT). Incorporation of vanadium ions into TiO2 yields a remarkable decrease of the energy offset between the conduction band edge of TiO2 and the lowest unoccupied molecular orbital of P3HT. The reduction of the ‘excess’ energy offset leads to a faster electron transfer at the interface of the bulk heterojunction with the lifetime decreasing from 30.2 to 19.7 ps, thus giving rise to a notable enhancement of the photovoltaic performance. That is, a power conversion efficiency of 3.01% for the vanadium-doped TiO2/P3HT solar cell at 5.0 wt% vanadium-doping is obtained as compared to 2.00% for pure TiO2.

We investigate the nonlinear optical properties of Cu 9 S 5 nanocrystals using the open aperture Z-scan method with 20 ps and 4 ns laser pulses at 532 nm. We found that optical nonlinearity arises from free carrier absorption in the former case, whereas in the latter it occurs mostly due to nonlinear scattering. Parameters characterizing free carrier absorption and nonlinear scattering were determined. The dynamics of the nonlinear processes was confirmed by pump-probe measurements with 20 ps pulses. Observation of optical limiting at both excitation time regimes indicates the potential of Cu 9 S 5 nanocrystals in laser safety devices.

We study a CW Ne–Ne laser-induced thermal diffusion and convection in a chloroaluminum phthalocyanine–ethanol solution by measuring the transmittance and deflection of the beam normally incident on the sample with the entrance surface parallel and normal to the optical table, respectively. In the former geometry, we find a monotonous increase of transmittance with time and no transmitted beam deflection. We quantitatively simulate the observed transmittance by involving thermal diffusion alone. In the latter geometry, we find a transition of transmittance from ascent to descent with time and a downward transmitted beam deflection. We additionally invoke convection to explain the results.

Using the Z-scan technique with 532 nm 19 ps laser pulses separated by two time intervals τp-p’s (0.1 s and 1.0 s) sandwiching the mass diffusion time constant of the C49H43ClO6 + 1,2 dichloroethane solution, we investigate short-pulse-induced solute migration in the sample by measuring its transmittance change with τp-p variation. Preparing the sample at two concentrations, we find that τp-p reduction, from 1.0 s to 0.1 s, increases its transmittance when input pulse energy e1 exceeds a threshold eT, which is lower for the dilute solution than the concentrated one. At two e1’s above eT for the dilute solution, τp-p-reduction-induced transmittance increase in the dilute solution, as compared to that in the concentrated solution, is more at the lower e1 and less at the higher e1. This differs from continuous-wave-driven thermal diffusion which always causes a larger transmittance increase in the concentrated solution by inducing a larger temperature gradient. From this study, we predict that solute migration induced by short pulses at 1064 nm is one of the undesired heating effects occurring when this solution is used to simultaneously Q-switch and mode-lock Nd:YAG lasers.

We investigated optical nonlinear refraction (NLR) of C2H4Cl2 and C2H4Br2 using the [Formula: see text]-scan technique with 532[Formula: see text]nm 17 picosecond pulses delivered at 10[Formula: see text]Hz. We found that the latter shows larger positive Kerr nonlinear refractive index than the former, [Formula: see text][Formula: see text]cm2/W versus [Formula: see text][Formula: see text]cm2/W. According to our additional study on time-resolved Raman-induced Kerr effect, this observed trend is ascribed to stronger inter-molecular motions of diffusive reorientation and polarizability distortion in C2H4Br2 than in C2H4Cl2. This study helps to understand the nonlinear response of molecular motions to electric-field in great details which have not been well-defined previously.

Using the Z-scan technique and a 532 nm TEM00 mode laser pulse with a width of 2.8 ns and a waist radius of 15.0 μm, we characterize photo absorption induced thermal lensing effect in a toluene solution of C60. To fit the experimental results, we have to strictly solve the thermal acoustic wave equation, driven by the temperature rise, to achieve the solvent density change. Steady state (instantaneous expansion) approximation of this wave equation greatly breaks the agreement of the theoretical simulation with the experimental results. Accordingly, the experimentally observed thermal lensing effect is assured in the transient regime.

We investigate nonlinear refraction of chloroaluminum phthalocyanine dissolved in ethanol using the Z-scan technique with 532-nm 19-ps laser pulses, separated by various time intervals with respect to the solution’s mass diffusion time constant. As a result, we verify that a negative lensing effect is induced by the outward solute migration, in agreement with our theoretical inference.

To explain the experimental observation that a short pulse with energy exceeding a threshold can induce the outward solute migration in an ethanolic solution of chloroaluminum phthalocyanine, we have modeled each solute molecule as an oscillator confined within a potential well formed by the attractive forces of neighboring solvent molecules. In this report, we further infer that the threshold increases with a decreasing solution temperature. This inference is verified by measuring the energy thresholds for a 19 picosecond pulse to induce the outward solute migration in this solution at two temperatures of 288 K and 293 K.

Using electrostatic self-assembly of a [CuPc(COOH)4]/polydiallyldimethylammonium chloride (PDDA) film, we demonstrate that signal fluctuation induced by a random surface inhomogeneity of less than 70 nm can be approximately resolved by a nonlinear-imaging technique with a phase object (NIT-PO) as opposed to Z-scan. In our NIT-PO simulation the sample is regarded as perfectly parallel, while the incident intensity distribution is modified to mimic that of an extremely weak laser beam traversing the sample, which is detected by a charge-coupled-device (CCD) camera. However, the original phase in the simulations is maintained, since phase distortions caused by the sample are not measurable at the CCD plane.

Room temperature luminescence in a CuI/AgI glass system is investigated by irradiating the system at 410 nm (3.02 eV). The spectrum peaks at 635 nm (1.95 eV) and 700 nm (1.77 eV), while the intensity is significantly enhanced (centered at 635 nm) by increasing the amount of AgI. We propose a model based on an increase in the AgI:Cu + species at higher AgI concentration at which the red emission is attributed to the radiative recombination from carriers trapped at the donor sites (e.g., interstitial silver ions) and the acceptor sites (e.g., a vacancy-compensated divalent cation). The PL efficiency is also estimated by comparison with a standard rhodamine B solution.

By chopping 820 nm 18 femtosecond (fs)-laser pulses, continuously generated by a self-mode locked Ti:Al2O3 laser at 82 MHz, into trains with both train-width and train-to-train separation considerably longer than the thermal diffusivity time constant τth of CS2, we conducted Z-scan measurements on it at various times relative to the leading pulse of each train (T's). As a result, we observed negative nonlinear refraction strengthening with T within τth and gradually stabilizing with T exceeding τth. We quantitatively explain the experimental results in terms of the thermal lensing effect. In particular, we attribute the heat generation to non-radiative relaxation of libration excited by individual 18 fs-pulses via stimulated Raman scattering. In contrast to the commonly held view of multi-photon excitation, we propose and verify a new heat-generating mechanism for the thermal lensing effect in CS2.

We experimentally verified fs laser pulse induced thermal lensing effect in CS2 with the Z-scan technique and explain this effect as a result of relaxation of stimulated Raman scattering excited libration.

The photoluminescence (PL) properties of CuBr and CuBr/AgBr semiconductor nanocrystals (NCs) embedded in borosilicate glasses are measured under band-to-band excitation by a 355-nm Nd YAG laser. We observed emission from CuBr (peaked at 520 nm) doped glass, which is associated with deep states in CuBr NCs. We also observed the sensitized blue to orange-red emission in CuBr/AgBr-glass systems (peaked at 520 and 570 nm), in which the luminescence intensity of CuBr decreases with increasing AgBr concentrations, while it is enhanced significantly around 570 nm. The results are discussed by the possible energy transfer between them, or by the multi-exitonic recombination process which ejects an excited carrier from CuBr to AgBr NCs.

Transient optical Kerr effect of liquids C2H4Cl2 and C2H4Br2 is investigated, for the first time to our knowledge, with a femtosecond (fs) probe laser delayed with respect to a coherent fs pump laser. Coherent coupling and electronic Kerr signals are observed around zero delay when pump and probe overlap. Persisting after the pump-probe overlap are Kerr signals arising from the torsional and other intramolecular vibrations of the trans and gauche conformations; Kerr signals arising from the intermolecular motion are also observed. Vibrational quantum interference is only observed in liquid C2H4Br2 and the related beats data are fitted with the torsional vibrations, 91 cm−1 (gauche) and 132 cm−1 (trans), and the CCBr angle-bending vibrations, 231 cm−1 (gauche) and 190 cm−1 (trans), with dephasing times, 0.45 ps, 0.45 ps, 2 ps, and 1.5 ps, respectively. These vibrational frequencies agree with those obtained in the frequency-domain. That no vibrational mode is observed for C2H4Cl2 might be attributed to ineffective Raman-pumping. Kerr signals observed after the pump-probe overlap are Fourier transformed to give the spectra of the intermolecular motion and the vibrational spectrum, which agrees with the one observed in the infrared absorption and/or Raman scattering heretofore.

CuI embedded in borosilicate glasses are prepared by a melt and heat-treatment method. We obtain the free carrier absorption cross section σ ≈ 1.0 × 10−17 cm2 and the two-photon absorption coefficient β ≈ 0.14 cm/GW by means of the Z-scan method using 6-ns laser pulses at 532 nm, with an irradiation I0 ≈ 16 MW/cm2. Upon excitation with 355 nm laser pulses at room temperature, very bright luminescence is observed, while the peak position shifts to lower energy as the band gap of CuI decreased by crystal growth. We also observed that the peak intensity varies linearly with the input intensity. The results could be attributed to the radiative recombination associated with traps or defects from impurities in the CuI microcrystallites.

Nonlinear absorption and refraction of C60 dissolved in toluene are investigated using the Z-scan technique with trains of picosecond laser pulses extending over ∼70 nanoseconds. Analysis of the experimental results, with a five-state model, assures contributions of the triplet–triplet absorption and the thermal effect induced by nonradiative relaxation, in addition to the singlet–singlet excitation verified in a previous picosecond study.

The pump–probe Raman-induced optical Kerr effect (RIKE) of simple molecular liquids, studied with femtosecond laser pulses, exhibit long lasting beats ascribable to vibrational quantum interference (QI). While energy conservation entails vibrational resonances in RIKE, momentum conservation boils down to wave vector-matching in the pump and probe processes, which calls for the participation of a vibrational excitation wave. The refractive index dispersion around vibrational resonances is intimately related to the focusing angle of the pump (also probe) beam. The larger the focusing angle, the greater the excitation wave number, i.e. the more energetic the vibration in resonance; if the focusing angle is too small, energetic vibrations cannot be observed in vibrational QI, even if energy conservation is fulfilled. If the pump and probe beams are perfectly collimated, then all beams must be collinear in order to conserve momentum.

Materials with strong reverse saturable absorption have been searched for power limiting applications, and metallophthalocyanine molecules are one of them. Here we report our investigations of reverse saturable absorptive properties of copper phthalocyanines with three different side substitutions. By dissolving them in toluene or incorporating them in polymer-silica hybrid material using a sol-gel process with polyvinyl butyral and tetraethyl orthosilicate as precursors, we found that substitution of copper phthalocyanines influence the optical nonlinearities. Regarding the preparation process of phthalocyanines in the solids, a new route has been successfully used.

The nonlinear optical (NLO) properties of lanthanide bisphthalocyanine (Lu(TBPc)Pc), including first hyperpolarizability, second hyperpolarizability and reverse saturable absorption (RSA), have been investigated. Furthermore, Lu(TBPc)Pc has also been applied for optical switch based on its RSA performance.

We have investigated reverse saturable absorption (RSA) of tetrakis(2,9,16,23-tert-butyllanthanide bisphthalocyanines)(M(TBPc)2, M=Lu, Dy, Tb) with Z-scan technique. Furthermore, lanthanide bisphthalocyanines have also been utilized for optical switches based on their RSA performance. However, the experimental results reveal that the performances of RSA and optical switches for M(TBPc)2 (M=Lu, Dy, Tb) are poorer than that of tetrakis(2,9,16,23-tert-butylcopper phthalocyanines) (Cu(TBPc)) due to strong intramolecular π–π interaction between the two Pc rings.

Soluble phthalocyanines, including tetrakis(2,9,16,23-cumylphenoxy) copper phthalocyanines (CuPc(β-CP)4), tetrakis(1,8,15,22-cumylphenoxy) copper phthalocyanines (CuPc(α-CP)4) as well as tetrakis(2,9,16,23-tert-butyl) copper phthalocyanines (CuPc(β-t-butyl)4), and porphyrins (5,10,15,20-tetrakis(4-tert-butylphenyl)porphyrins; M(TBP), M=H2, Zn, Cu, Mg, InCl, AlCl) have been quickly synthesized by microwave irradiation. Furthermore, their reverse saturable absorption have also been investigated by dissolving them in solvent or incorporating them in polymer-silica hybrid material with a sol–gel process with polyvinyl butyral and tetraethyl orthosilicate as precursors. A new method for the preparation process of phthalocyanines and porphyrins in the solids has been successfully used.

The spectroscopy and dynamics of the low-lying triplet state of the proton-transfer tautomer in salicylaldehydes have been studied via internal heavy-atom effects coupled with a sensitive near-IR detecting system. For 3,5-diiodosalicylaldehyde a weak proton-transfer keto-tautomer phosphorescence was resolved with a maximum at 710 nm ( τ p ∼1.8 μs , Φ obs ∼5.23×10 −4 ) in a 77 K methylcyclohexane glass. The results, in combination with the time-resolved thermal lensing experiment, further deduced the triplet-state population yield and radiative decay rate to be 0.20 (298 K) and 3.12×10 2 s −1 , respectively. Consequently, the energetics and dynamics of the triplet states during a proton transfer cycle are discussed in detail.

Using the Z-scan technique, we study the nonlinear interaction of a dilute methanolic solution of chloro-aluminum phthalyocyanine with a ∼70 ns long train of laser pulses, each of 18 ps duration. The observations are explained by taking into account, in addition to the photoexcitation of a ground state molecule by a single pulse, thermal lensing and photoabsorption by an excited molecule (singlet or triplet) produced by previous pulses. A microscopic picture of the heating process in the solution is provided.

In this work, dysprosium ion decorated yttrium oxide (Dy(3+):Y2O3) nanocrystal phosphors were incorporated into TiO2 acceptor thin film in a bid to enhance the light harvest, charge separation and transfer in the hybrid solar cells. The results show that the energy level offset between the donor (P3HT) and the acceptor (Dy(3+):Y2O3-TiO2) has been narrowed down, thus leading to the enhanced electron and hole transports, and also photovoltaic performances as compared to pure TiO2 without incorporating Dy(3+):Y2O3. By applying femtosecond transient optical spectroscopy, after the incorporation of dopant Dy(3+):Y2O3 into TiO2 at 6 wt%, both the hot electron and hole transfer lifetimes have been shortened, that is, from 30.2 ps and 6.94 ns to 25.1 ps and 1.26 ns, respectively, and an enhanced efficiency approaching 3% was achieved as compared to 2.0% without doping, indicating that the energetic charges are captured more efficiently benefitting a higher power conversion efficiency. Moreover, these results reveal that both the conduction band (CB) and valence band (VB) edges of the acceptor were elevated by 0.57 and 0.32 eV, respectively, after incorporating 6 wt% Dy(3+):Y2O3. This work demonstrates that distinct energy level alignment engineered by Dy(3+):Y2O3 phosphor has an important role in pursuing efficient future solar cells and underscores the promising potential of rare-earth phosphor in solar applications.

Highly efficient hot electron transport represents one of the most important properties required for applications in photovoltaic devices. Whereas the fabrication of efficient hot electron capture and lost-cost devices remains a technological challenge, regulating the energy level of acceptor-donor system through the incorporation of foreign ions using the solution-processed technique is one of the most promising strategies to overcome this obstacle. Here we present a versatile acceptor-donor system by incorporating MoO3:Eu nanophosphors, which reduces both the ‘excess' energy offset between the conduction band of acceptor and the lowest unoccupied molecular orbital of donor, and that between the valence band and highest occupied molecular orbital. Strikingly, the hot electron transfer time has been shortened. This work demonstrates that suitable energy level alignment can be tuned to gain the higher hot electron/hole transport efficiency in a simple approach without the need for complicated architectures. This work builds up the foundation of engineering building blocks for third-generation solar cells.

In this work, a core-shell nanostructure of samarium phosphates encapsulated into a Eu(3+)-doped silica shell has been successfully fabricated, which has been confirmed by X-ray diffraction, transmission electron microscopy (TEM), and high-resolution TEM. Moreover, we report the energy transfer process from the Sm(3+) to emitters Eu(3+) that widens the light absorption range of the hybrid solar cells (HSCs) and the strong enhancement of the electron-transport of TiO2/poly(3-hexylthiophene) (P3HT) bulk heterojunction (BHJ) HSCs by introducing the unique core-shell nanoarchitecture. Furthermore, by applying femtosecond transient absorption spectroscopy, we successfully obtain the electron transport lifetimes of BHJ systems with or without incorporating the core-shell nanophosphors (NPs). Concrete evidence has been provided that the doping of core-shell NPs improves the efficiency of electron transfers from donor to acceptor, but the hole transport almost remains unchanged. In particular, the hot electron transfer lifetime was shortened from 30.2 to 16.7 ps, i.e., more than 44% faster than pure TiO2 acceptor. Consequently, a notable power conversion efficiency of 3.30% for SmPO4@Eu(3+):SiO2 blended TiO2/P3HT HSCs is achieved at 5 wt % as compared to 1.98% of pure TiO2/P3HT HSCs. This work indicates that the core-shell NPs can efficiently broaden the absorption region, facilitate electron-transport of BHJ, and enhance photovoltaic performance of inorganic/organic HSCs.

Low-temperature solution-processed photovoltaics suffer from low efficiencies because of poor exciton or electron-hole transfer. Inorganic/organic hybrid solar cell, although still in its infancy, has attracted great interest thus far. One of the promising ways to enhance exciton dissociation or electron-hole transport is the doping of lanthanide phosphate ions. However, the underlying photophysical mechanism remains poorly understood. Herein, by applying femtosecond transient absorption spectroscopy, we successfully distinguished hot electron, less energetic electron, hole transport from electron-hole recombination. Concrete evidence has been provided that lanthanide phosphate doping improves the efficiency of both hot electron and "less energetic" electron transfers from donor to acceptor, but the hole transport almost remains unchanged. In particular, the hot electron transfer lifetime was shortened from 30.2 to 12.7 ps, that is, more than 60% faster than pure TiO2 acceptor. Such improvement was ascribed to the facts that the conduction band (CB) edge energy level of TiO2 has been elevated by 0.2 eV, while the valence band level almost remains unchanged, thus not only narrowing the energy offset between CB levels of TiO2 and P3HT, but also meanwhile enlarging the band gap of TiO2 itself that permits one to inhibit electron-hole recombination within TiO2. Consequently, lanthanide phosphate doped TiO2/P3HT bulk-heterojunction solar cell has been demonstrated to be a promising hybrid solar cell, and a notable power conversion efficiency of 2.91% is therefore attained. This work indicates that lanthanide compound ions can efficiently facilitate exciton generation, dissociation, and charge transport, thus enhancing photovoltaic performance.

The surface vibrational spectroscopy of ethanol (C2H5OH, ethyl alcohol): water binary mixture, or the aqueous solution of ethanol, is investigated via sum frequency generation (SFG) in the OH region (3000 to 3900 cm−1). The bulk molar ratio of the ethanol is varied from x = 0.0024 to 0.20. Our concentration dependence results support the statement that the surface density of water molecules with a free dangling OH bond is about 25% in the air/water interface. It also indicates that the ethyl group of the surface ethanol molecules sticks out above the nominal surface, while the hydroxyl group alone is immersed in the mixture solution. And the surface layer is a mixed monolayer. We have demonstrated here that a LiNbO3 crystal containing -OH can be sufficient for the SFG spectroscopy measurement in the -OH region regardless of its absorption dip.

Nonlinear absorptive and refractive properties of C60/toluene solution are studied using the Z-scan technique and a 532 nm laser delivering single picosecond (ps) pulses and trains of ps pulses separated by 7 nanoseconds (ns). With single ps pulses, reverse saturable absorption and positive nonlinear refraction are observed and attributed to population transitions among the singlet states. With ps pulse trains, a sign change of nonlinear refraction relative to that of single ps-pulse excitation is observed and is attributed to heat-induced temperature rise and population relaxing to triplet states.

Using the Z -scan technique with 532 nm laser pulses of dual widths in the picosecond regime, we distinguish between two-photon absorption (TPA) and excited state absorption (ESA). To account for reverse saturable absorption in chloro-aluminum phthalocyanine dissolved in methanol both TPA and ESA, rather than either one, need be invoked.

The ultrafast inter- and intramolecular dynamics of liquid CBrCl3 are studied with a femtosecond laser in a pump/probe optical Kerr experiment. The prompt part of the observed Kerr signal is found to comprise not just electronic response but also coherent coupling. As reported in the literature, the weak and delayed part of the signal is attributed to three kinds of intermolecular dynamics: diffusive reorientation, polarizability distortion, and molecular libration with decay times, respectively, of 2 ps, 500 fs, and 190 fs. Included in the delayed Kerr signal are long lasting oscillations which are ascribed to quantum interference involving four normal vibrations of the molecule. By a careful fitting of both the time domain (Kerr) and frequency domain (Raman) data with existing theories the four vibrations are identified as ν2 = 422 cm−1, ν3 = 246 cm−1, ν5 = 295 cm−1, and ν6 = 191 cm−1, with dephasing times, 1.1 ps, 1.7 ps, 1 ps, and 1 ps, respectively.

Using the C60 fluorescence as a reference in combination with the direct spectroscopic observation of 1O2 visible emission, the photophysics of 1O2 dimol ((1Δg)2) and O2(1 ) states in solution has been studied. The quantum yield of O2 1 → 3 (765 nm) emission has been measured to be 1.94 × 10-7, and consequently, the radiative decay rate of 1 → 3 transition was determined to be 1.55 ± 0.04 s-1 which, within the experimental error, is consistent with the previous report of 0.46 s-1.4 Further determination of the ratio between radiative decay and dissociation rates of the 1Δg dimol has been achieved by comparing the dimol (1Δg)2 → (3 )2 emission intensity with the tetra-tert-butylphthalocyanine delayed fluorescence induced by a two-step energy transfer from the O2(1Δg) state. As a result, the lower limit of the dissociation rate constant of the dimol was estimated to be (2.6 ± 0.3) × 1010 s-1 in CCl4.

We investigated picosecond nonlinear refraction of simple liquids C2H4Cl2 and C2H4Br2 with the Z-scan technique and explained the results in virtue of various molecular motions verified by femtosecond RIKE technique.

A short laser pulse with energy exceeding a threshold can induce the outward solute migration. In this study we further verify that application of a temperature gradient along the light propagation direction impedes this migration.

We report a novel method of determining the lifetimes of the high-lying excited singlet states of dye molecules in solution. The method is based on simulating the Z-scan technique with ground-state and excited-state absorptions of an incident laser pulse having Gaussian temporal and spatial distributions. This leads to the important finding that the use of laser pulses as long as tens of picoseconds can resolve subpicosecond lifetime.