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Luminescence upconversion nanocrystals capable of converting two low-energy photons into a single photon at a higher energy are sought-after for a variety of applications, including bioimaging and photovoltaic light harvesting. Currently available systems, based on rare-earth-doped dielectrics, are limited in both tunability and absorption cross-section. Here we present colloidal double quantum dots as an alternative nanocrystalline upconversion system, combining the stability of an inorganic crystalline structure with the spectral tunability afforded by quantum confinement. By tailoring its composition and morphology, we form a semiconducting nanostructure in which excited electrons are delocalized over the entire structure, but a double potential well is formed for holes. Upconversion occurs by excitation of an electron in the lower energy transition, followed by intraband absorption of the hole, allowing it to cross the barrier to a higher energy state. An overall conversion efficiency of 0.1% per double excitation event is achieved.

Nanosecond timescale underwater electrical wire explosions of ring-shaped Cu wires were investigated using a pulsed generator with a current amplitude up to 50 kA. It was shown that this type of wire explosion results in the generation of a toroidal shock wave (SW). Time- and space-resolved optical diagnostics were used to determine azimuthal uniformity of the shock wave front and its velocity. It was found that the shock wave preserves its circular front shape in the range of radii 50 μm<r<5 mm. At r≤15μm, azimuthal irregularities of the SW front were obtained indicating the appearance of azimuthal instability. A surprising finding is that the shock wave propagates with a constant velocity of vsw=1.2M, where M is the Mach number. The dynamics of the leading part of the shock wave, based on the oblique shock wave theory, is presented, explaining the constant velocity of the shock wave.

Benzhydryl radicals and cations are reactive intermediates central to the under-standing of organic reactivity. They can be generated from benzhydryl halides by UV irradi-ation. We performed transient absorption (TA) measurements over the range from femto -seconds to microseconds to unravel the complete reaction scheme. The 290–720-nm proberange allows the unambiguous monitoring of all fragments. The appearance of the radical isdelayed to the optical excitation, the onset of the cation signal is found even later. Ab initiocalculations show that this non-rate behavior in the 100 fs range is due to wavepacket motionfrom the Franck–Condon region to two distinct conical intersections. The rise of the opticalsignal with a quasi-exponential time of 300 fs is assigned to the planarization and solvationof the photoproducts. The bond cleavage predominantly generates radical pairs. A subse-quent electron transfer (ET) transforms radical pairs into ion pairs. Due to the broad inter-radical distance distribution and the distance dependence, the ET is strongly non-exponen-tial. Part of the ion pairs recombine geminately. The ET and the recombination are terminatedby the depletion of close pairs and diffusional separation. The remaining free radicals and cations undergo further reactions in the nanosecond to microsecond regime.

The lack of understanding of the temporal effects and the restricted ability to control experimental conditions in order to obtain intrinsic spectral lineshapes in surface sum-frequency generation vibrational spectroscopy (SFG-VS) have limited its applications in surface and interfacial studies. The emergence of high-resolution broadband sum-frequency generation vibrational spectroscopy (HR-BB-SFG-VS) with sub-wavenumber resolution [Velarde et al., J. Chem. Phys., 2011, 135, 241102] offers new opportunities for obtaining and understanding the spectral lineshapes and temporal effects in SFG-VS. Particularly, the high accuracy of the HR-BB-SFG-VS experimental lineshape provides detailed information on the complex coherent vibrational dynamics through direct spectral measurements. Here we present a unified formalism for the theoretical and experimental routes for obtaining an accurate lineshape of the SFG response. Then, we present a detailed analysis of a cholesterol monolayer at the air/water interface with higher and lower resolution SFG spectra along with their temporal response. With higher spectral resolution and accurate vibrational spectral lineshapes, it is shown that the parameters of the experimental SFG spectra can be used both to understand and to quantitatively reproduce the temporal effects in lower resolution SFG measurements. This perspective provides not only a unified picture but also a novel experimental approach to measuring and understanding the frequency-domain and time-domain SFG response of a complex molecular interface.

Dye-sensitized solar cells are a promising alternative to traditional inorganic semiconductor-based solar cells. Here we report an open-circuit voltage of over 1,000 mV in mesoscopic dye-sensitized solar cells incorporating a molecularly engineered cobalt complex as redox mediator. Cobalt complexes have negligible absorption in the visible region of the solar spectrum, and their redox properties can be tuned in a controlled fashion by selecting suitable donor/acceptor substituents on the ligand. This approach offers an attractive alternate to the traditional I₃⁻/I⁻ redox shuttle used in dye-sensitized solar cells. A cobalt complex using tridendate ligands [Co(bpy-pz)₂]^3+/2+(PF₆)_3/2 as redox mediator in combination with a cyclopentadithiophene-bridged donor-acceptor dye (Y123), adsorbed on TiO₂, yielded a power conversion efficiency of over 10% at 100 mW cm⁻². This result indicates that the molecularly engineered cobalt redox shuttle is a legitimate alternative to the commonly used I₃⁻/I⁻ redox shuttle.

We present a visible-infrared sum-frequency spectroscopic technique that is capable of simultaneously determining the magnitude and phase of the sample response from a single set of experimental conditions. This is especially valuable in cases where the phase stability is high, as in collinear beam geometries, as it enables multiple experiments to be performed without re-measuring the local oscillator phase or the reference phase. After illustrating the phase stability achievable with such a geometry, we provide a technique for quantitatively determining the magnitude and phase from a single set of two-dimensional spectral-temporal interference fringes. A complete demonstration is provided for the C–H stretching frequency region at the surface of an octadecyltricholosilane film.

The Pan-STARRS1 survey is collecting multi-epoch, multi-color observations of the sky north of declination −30° to unprecedented depths. These data are being photometrically and astrometrically calibrated and will serve as a reference for many other purposes. In this paper, we present our determination of the Pan-STARRS1 photometric system: g_P1, r_P1, i_P1, z_P1, y_P1, and w_P1. The Pan-STARRS1 photometric system is fundamentally based on the Hubble Space Telescope Calspec spectrophotometric observations, which in turn are fundamentally based on models of white dwarf atmospheres. We define the Pan-STARRS1 magnitude system and describe in detail our measurement of the system passbands, including both the instrumental sensitivity and atmospheric transmission functions. By-products, including transformations to other photometric systems, Galactic extinction, and stellar locus, are also provided. We close with a discussion of remaining systematic errors.

The ability to achieve sub-wavenumber resolution (0.6 cm⁻¹) and a large signal-to-noise ratio in high-resolution broadband sum-frequency generation vibrational spectroscopy (HR-BB-SFG-VS) allows for the detailed SFG spectral lineshapes to be used in the unambiguous determination of fine spectral features. Changes in the structural spectroscopic phase in SFG-VS as a function of beam polarization and experimental geometry proved to be instrumental in the identification of an unexpected 2.78 ± 0.07 cm⁻¹ spectral splitting for the two methyl groups at the vapor/dimethyl sulfoxide (DMSO, (CH₃)₂SO) liquid interface as well as in the determination of their orientational angles.

Laser induced breakdown spectroscopy (LIBS) provides the opportunity to analyze almost any element, from any material, in any environment. Among the many applications of LIBS is the analysis of thin films and multilayered structures. An automated system was designed and built to conduct LIBS using Nd:YAG and Ti:Sapphire lasers, broadband and high-resolution spectrometers and detectors. This system incorporates the sample manipulation as well as laser and spectrometer control and timing.

A series of experiments were conducted to analyze the ability of nanosecond and femtosecond lasers to detect Mg impurities in thin TiO₂ films using LIBS. It was determined that optimal detection occurs early in the plasma ionic/atomic emission with detection capabilities in the parts-per-million range. Another series of experiments were conducted using LIBS to analyze thin transparent organic films, with specific emphasis on the effect of film thickness and interplay between film and substrate. The challenges of ablating and measuring multiple layers have also been explored using various laser wavelengths. The effectiveness of LIBS has been demonstrated for depth profiling of CIGS solar cells. Ablation crater and ablation threshold analysis aided in understanding and overcoming some of the obstacles in depth profiling. One of the challenges with LIBS is the identification and mitigation of matrix effects. This problem was explored using a Mg tracer element and various compositions of the suspected elements Si, Ca, and Sr which can cause errors in LIBS analysis. The goal of this dissertation is to investigate the ability of LIBS to conduct detailed thin film analysis for a variety of materials and potential applications. This includes analyzing trace elements from a traditionally noisy background, measuring difficult to ablate thin films, and the unique challenges associated with multilayered structures.

In this work Er³⁺ doped NaLaF₄ material has been synthesized Along with the description of the synthesis route, luminescence spectra and decay kinetics of both traditional and up-conversion luminescence of Er³⁺ will be presented for different Er³⁺ doping levels. It will be shown that the main mechanisms involved in the creation of the up-conversion luminescence in NaLaF₄:Er³⁺ under excitation at about 975 nm are excited state absorption and energy transfer. Relative impact of either of the mechanisms in NaLaF₄:Er³⁺ depends on both the concentration of Er³⁺ and on the excitation wavelength: the increase of either the concentration or the excitation wavelength leads to the prevalence of energy transfer mechanism over excited state absorption mechanism.