The fabrication and characterization of boron-doped diamond microelectrodes for use in electrochemical detection coupled with capillary electrophoresis (CE-EC) is discussed. The microelectrodes were prepared by coating thin films of polycrystalline diamond on electrochemically sharpened platinum wires (76-, 25-, and 10-microm diameter), using microwave-assisted chemical vapor deposition (CVD). The diamond-coated wires were attached to copper wires (current collectors), and several methods were explored to insulate the cylindrical portion of the electrode: nail polish, epoxy, polyimide, and polypropylene coatings. The microelectrodes were characterized by scanning electron microscopy, Raman spectroscopy, and cyclic voltammetry. They exhibited low and stable background currents and sigmoidally shaped voltammetric curves for Ru(NH3)6(3+/2+) and Fe(CN)6(3-/4-) at low scan rates. The microelectrodes formed with the large diameter Pt and sealed in polypropylene pipet tips were employed for end-column detection in CE. Evaluation of the CE-EC system and the electrode performance were accomplished using a 10 mM phosphate buffer, pH 6.0, run buffer, and a 30-cm-long fused-silica capillary (75-microm i.d.) with dopamine, catechol, and ascorbic acid serving as test analytes. The background current (approximately 100 pA) and noise (approximately 3 pA) were measured at different detection potentials and found to be very stable with time. Reproducible separation (elution time) and detection (peak current or area) of dopamine, catechol, and ascorbic acid were observed with response precisions of 4.1% or less. Calibration curves constructed from the peak area were linear over 4 orders of magnitude, up to a concentration between 0.1 and 1 mM. Mass limits of detection for dopamine and catechol were 1.7 and 2.6 fmol, respectively (S/N = 3). The separation efficiency was approximately 33,000, 56,000, and 98,000 plates/m for dopamine, catechol, and ascorbic acid, respectively. In addition, the separation and detection of 1- and 2-naphthol in 160 mM borate buffer, pH 9.2, was investigated. Separation of these two analytes was achieved with efficiencies of 118,000 and 126,000 plates/m, respectively.

CsPbI3 perovskite quantum dots (QDs) are more unstable over time as compared to other perovskite QDs, owing to ligand loss and phase transformation. The strong red emission from fresh CsPbI3 QDs gradually declines to a weak emission from aged QDs, which PLQY dropped by 93% after a 20 day storage; finally, there is no emission from δ-phase CsPbI3. The present study demonstrated a facile surface treatment method, where a sulfur–oleylamine (S-OLA) complex was utilized to passivate the defect-rich surface of the CsPbI3 QDs and then self-assembly to form a matrix outside the CsPbI3 QDs protected the QDs from environmental moisture and solar irradiation. The PLQY of the treated CsPbI3 QDs increased to 82.4% compared to initial value of 52.3% of the fresh QDs. Furthermore, there was a significant increase in the colloidal stability of the CsPbI3 QDs. Above 80% of the original PLQY of the treated QDs was reserved after a 20 day storage and the black phase could be maintained for three months before transforming to the yellow phase. The introduction of S-OLA induced the recovery of the lost photoluminescence of the nonluminous aged CsPbI3 QDs with time to 95% of that of the fresh QDs. Furthermore, the photoluminescence was maintained for one month. The increase in the stability and photoluminescence are critical for realizing high-performance perovskite-QD-based devices. Therefore, this work paves the way for increasing the performance of perovskite-based devices in the near future.

for the red, green, and blue (RGB) colors but incorporates white light sources, which can be further converted to RGB emission using color filters (CFs). Recent commercialized televisions and computer monitors generally use down-converted displays (DCDs), in which color conversion phosphor films and CFs are laid atop the blue BLU to change its emission to the desired color. Semiconductor nano particles (NPs) such as cadmium (Cd) quantum dots (QDs) and indium phosphide (InP) QDs with narrow spectral bandwidth, high luminous efficiency, and easy tunable wavelength have been recently introduced as more suitable materials for display application than the yttrium aluminum garnet (YAG) phosphors that are widely used at present. QDs have good color purity, but users demand still higher color purity displays that can represent realistic colors. [1-7] Metal-halide perovskites (shortly, perovskite) have simple crystal structures of ABX 3 or A 2 BX 4 (where A is an organic ammonium (e.g., methylammonium (MA; CH 3 NH 3 +) and formamidinium (FA; CH(NH 2) 2 +)) or an alkali metal cation (e.g., Cs +), B is a transition metal cation (e.g., Pb 2+), and X is a halide anion (I − , Br − , and Cl −) [8] (Figure 1a). Perovskite emitters have higher color purity (color gamut ≥ 140% in National Television Standards Committee (NTSC) TV color standard and ≥95% in International Telecommunication Union (ITU) Recommendation Rec. 2020 standard) than inorganic QDs emitters (full width at half maximum (FWHM) ≈ 30 nm; color gamut ≈ 110-115% in NTSC standard and <90% in Rec. 2020 standard). However, perovskite have low exciton binding energy (≈30-50 meV in MAPbI 3 and ≈76 meV in MAPbBr 3), so most of electron-hole pairs are dissociated into free charge carriers, reducing radiative recombination and photoluminescence quantum yield (PLQY) at room temperature. Perovskite nanoparticles (PeNPs) are highly bright [8] and have unique optical and physical properties such as facile emission wavelength tunability, narrow FWHM, and high PLQY (≥95%) compared to inorganic QDs and organic emitters (Figure 1b) [8] and high absorption coefficient compared to inorganic QDs. Therefore, many researchers have tried to use them as light emitters. However, perovskite emitters have limitations when applied to DCDs. First, polar organic solvents or water cause structural changes in perovskites and consequent loss of optical properties. Second, environmental factors such as moisture, heat, light, and oxygen degrade perovskite emitters. Methods to overcome the instability of perovskites to moisture, light, and heat in down-converted displays (DCDs), in which films of perovskite emitters are placed on top of the backlight unit and convert its light to a desired color, are reviewed here. First, the photophysical properties of perovskite emitters as light converters in DCDs are discussed. Second, five strategies to improve stability of perovskite emitting materials (PeMs) mostly in a form of perovskite nanoparticles (PeNPs) are summarized: i) encapsulation in inorganics, ii)...

Layered Ruddlesden–Popper perovskite (RPP) photovoltaics have gained substantial attention owing to their excellent air stability. However, their photovoltaic performance is still limited by the unclear real-time charge-carrier mechanism of operating...