Origin of the Broadband Photoluminescence of Pristine and Cu⁺/Ag⁺‑Doped Ultrasmall CdS and CdSe/CdS Quantum Dots

Ultrasmall (∼2 nm) copper­(I)- and silver­(I)-doped CdS and core/shell CdSe/CdS quantum dots (QDs) stabilized by Cd­(II) complexes with mercaptoacetate anions and ammonia were produced in aqueous solutions. The doped QDs emit broadband visible photoluminescence (PL) with a quantum yield reaching 10–12% for Cu⁺-doped QDs and 5–9% for Ag⁺-doped QDs. The broadband PL was described by a self-trapped exciton model as a sequence of phonon replicas of a zero-phonon emission line. The shape of the PL bands of CdS, Cu⁺-doped CdS QDs, and Ag⁺-doped CdS QDs was modeled by using the energies of optical phonons of CdS, CuS, and Ag₂S, respectively. The dependence of the average PL lifetime of both pristine and doped CdS and CdSe/CdS QDs on PL registration wavelength was interpreted in terms of the vibrational relaxation of the self-trapped exciton. The analysis of PL properties of different ultrasmall metal chalcogenide QDs showed that the broadband PL can be described by a general model which does not require the assumption of participation of charge-trapping lattice defects

Profiling Convoluted Single-Dimension Proton NMR Spectra: A Plackett–Burman Approach for Assessing Quantification Error of Metabolites in Complex Mixtures with Application to Cell Culture

Single-dimension hydrogen, or proton, nuclear magnetic resonance spectroscopy (1D-¹H NMR) has become an attractive option for characterizing the full range of components in complex mixtures of small molecular weight compounds due to its relative simplicity, speed, spectral reproducibility, and noninvasive sample preparation protocols compared to alternative methods. One challenge associated with this method is the overlap of NMR resonances leading to “convoluted” spectra. While this can be mitigated through “targeted profiling”, there is still the possibility of increased quantification error. This work presents the application of a Plackett–Burman experimental design for the robust estimation of precision and accuracy of 1D-¹H NMR compound quantification in synthetic mixtures, with application to mammalian cell culture supernatant. A single, 20 sample experiment was able to provide a sufficient estimate of bias and variability at different metabolite concentrations. Two major sources of bias were identified: incorrect interpretation of singlet resonances and the quantification of resonances from protons in close proximity to labile protons. Furthermore, decreases in measurement accuracy and precision could be observed with decreasing concentration for a small fraction of the components as a result of their particular convolution patterns. Finally, the importance of a priori concentration estimates is demonstrated through the example of interpreting acetate metabolite trends from a bioreactor cultivation of Chinese hamster ovary cells expressing a recombinant antibody

Origin and Dynamics of Highly Efficient Broadband Photoluminescence of Aqueous Glutathione-Capped Size-Selected Ag–In–S Quantum Dots

The 2–3 nm size-selected glutathione-capped Ag–In–S (AIS) and core/shell AIS/ZnS quantum dots (QDs) were produced by precipitation/redissolution from an aqueous colloidal ensemble. The QDs reveal broadband photoluminescence (PL) with a quantum yield of up to 60% for the most populated fraction of the core/shell AIS/ZnS QDs. The PL band shape can be described by a self-trapped exciton model implying the PL band being a sequence of phonon replica of a zero-phonon line resulting from strong electron–phonon interaction and a partial conversion of the electron excitation energy into lattice vibrations. It can be concluded that the position and shape of the PL bands of AIS QDs originate not from energy factors (depth and distribution of trap states) but rather from the dynamics of the electron–phonon interaction and the vibrational relaxation in the QDs. The rate of vibrational relaxation of the electron excitation energy in AIS QDs is found to be size-dependent, increasing almost twice from the largest to the smallest QDs

Nonaqueous Atomic Layer Deposition of Aluminum Phosphate

Aluminum phosphate was deposited onto bundles of carbon fibers and flat glassy carbon substrates using atomic layer deposition by exposing them to alternating pulses of trimethylaluminum and triethylphosphate vapors. Energy dispersive X-ray spectroscopy (EDXS) and solid state nuclear magnetic resonance (SS-NMR) spectra confirmed that the coating comprises aluminum phosphate (orthophosphate as well as other stoichiometries). Scanning electron microscopic (SEM) images revealed that the coatings are uniform and conformal. After coating, the fibers are still separated from each other like the uncoated fibers. Thermogravimetric analysis (TGA) indicates an improvement of oxidation resistance of the coated fibers compared to uncoated fibers