Elizabeth R. Young

Alternating layer addition approach to CdSe/CdS core/shell quantum dots with near-unity quantum yield and high on-time fractions

We report single-particle photoluminescence (PL) intermittency (blinking) with high on-time fractions in colloidal CdSe quantum dots (QD) with conformal CdS shells of 1.4 nm thickness, equivalent to approximately 4 CdS monolayers. All QDs observed displayed on-time fractions > 60% with the majority > 80%. The high-on-time-fraction blinking is accompanied by fluorescence quantum yields (QY) close to unity (up to 98% in an absolute QY measurement) when dispersed in organic solvents and a monoexponential ensemble photoluminescence (PL) decay lifetime. The CdS shell is formed in high synthetic yield using a modified selective ion layer adsorption and reaction (SILAR) technique that employs a silylated sulfur precursor. The CdS shell provides sufficient chemical and electronic passivation of the QD excited state to permit water solubilization with greater than 60% QY via ligand exchange with an imidazole-bearing hydrophilic polymer.

Photo-assisted water oxidation with cobalt-based catalyst formed from thin-film cobalt metal on silicon photoanodes

Integrating chemical catalysts for water splitting with photoanode materials is a longstanding challenge in demonstrating light-assisted water oxidation, a process which can be used for the generation of solar fuels. In this work we use a silicon photoanode as a substrate for processing cobalt metal films to form a cobalt-based water oxidation catalyst (Co–Pi) integrated with the silicon photoanode. The Co–Pi coated photoanodes show catalytic onset at 0.85 V under illumination, which is better than silicon photoanodes coated with ITO and solution-deposited Co–Pi (catalytic onset at 1.05 V) and significantly better photoanodes with only ITO contacts (catalytic activity onset at 1.6 V).

Direct formation of a water oxidation catalyst from thin-film cobalt

A cobalt-based water oxidation catalyst may be grown from sputter-deposited thin films (800 nm thick) of cobalt metal on a non-conductive glass substrate. Chemical composition and function of the catalyst prepared in this manner are similar to that for catalyst films prepared by electrodeposition of the catalyst from aqueous solutions of Co2+ salts. The method permits water oxidation catalysis to be established from protective barrier layers on materials that otherwise experience corrosion under the aqueous oxidative conditions.

Stabilized CdSe-CoPi Composite Photoanode for Light-Assisted Water Oxidation by Transformation of a CdSe/Cobalt Metal Thin Film

Integration of water splitting catalysts with visible-light-absorbing semiconductors would enable direct solar-energy-to-fuel conversion schemes such as those based on water splitting. A disadvantage of some common semiconductors that possess desirable optical bandgaps is their chemical instability under the conditions needed for oxygen evolution reaction (OER). In this study, we demonstrate the dual benefits gained from using a cobalt metal thin-film as the precursor for the preparation of cobalt-phosphate (CoPi) OER catalyst on cadmium chalcogenide photoanodes. The cobalt layer protects the underlying semiconductor from oxidation and degradation while forming the catalyst and simultaneously facilitates the advantageous incorporation of the cadmium chalcogenide layer into the CoPi layer during continued processing of the electrode. The resulting hybrid material forms a stable photoactive anode for light-assisted water splitting.

Lasing through a strongly-coupled mode by intra-cavity pumping

We demonstrate room temperature lasing through the polaritonic mode of a J-aggregate microcavity in which losses from exciton-exciton annihilation and slow polariton relaxation typical of direct J-aggregate excitation are circumvented via intra-cavity pumping. The pumping scheme utilizes an organic dye layer (DCM) within the cavity with an emission band overlapping the entire lower J-aggregate polariton branch spectrum, hence forcing DCM lasing to occur through the strongly-coupled mode. This cavity architecture, which separates strong coupling and gain into two materials, presents a general and flexible design for polariton devices and allows for the use of a wide range of materials, organic and inorganic, to be integrated into the cavity.

Spectral observation of conversion between ionized vs. non-ionized proton-coupled electron transfer interfaces

Two-point hydrogen bonding between acid and base functionalities provides a convenient method for the modular assembly of proton-coupled electron transfer (PCET) networks, especially when that interface comprises an amidinium and two-point anionic partner; a system is presented that permits the proton configuration within the interface to be determined when pK(a) values of the conjugate acids are known.

Fluorescence Enhancement Through Incorporation of Chromophores in Polymeric Nanoparticles

Incorporation of a pyrene chromophore on the surface of polymeric nanoparticles results in its fluorescence enhancement. Quantum yield and lifetime measurements suggest that the enrichment in fluorescent signal is due to the increase in the rigidity of the environment surrounding the fluorophores and that it is dependent on the particle size.