An official website of the United States government
Exciton dynamics o perovskite nanoclusters has been investigated or the rst time using emtosecond transient absorption (TA) and time-resolved photoluminescence (TRPL) spectroscopy. The TA results show two photoinduced absorption signals at 420 and 461 nm and a photoinduced bleach (PB) signal at 448 nm. The analysis o the PB recovery kinetic decay and kinetic model uncovered multiple processes contributing to electron−hole recombination. The ast component (∼8 ps) is attributed to vibrational relaxation within the initial excited state, and the medium component (∼60 ps) is attributed to shallow carrier trapping. The slow component is attributed to deep carrier trapping rom the initial conduction band edge (∼666 ps) and the shallow trap state (∼40 ps). The TRPL reveals longer time dynamics, with modeled lietimes o 6.6 and 93 ns attributed to recombination through the deep trap state and direct band edge recombination, respectively. The signicant role o exciton trapping processes in the dynamics indicates that these highly conned nanoclusters have deect-rich suraces.
more »
« less
Formation of Highly Oxidized Molecules from NO 3 Radical Initiated Oxidation of Δ-3-Carene: A Mechanistic Study
- Award ID(s):
- 1762098
- PAR ID:
- 10149004
- Date Published:
- Journal Name:
- ACS Earth and Space Chemistry
- Volume:
- 3
- Issue:
- 8
- ISSN:
- 2472-3452
- Page Range / eLocation ID:
- 1460 to 1470
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Two novel ternary compounds from the pseudobinary CH3NH3X–AgX (X = Br, I) phase diagrams are reported. CH3NH3AgBr2 and CH3NH3Ag2I3 were synthesized via solid state sealed tube reactions and the crystal structures were determined through a combination of single crystal and synchrotron X-ray powder diffraction. Structurally, both compounds consist of one-dimensional ribbons built from silvercentered tetrahedra. The structure of CH3NH3AgBr2 possesses orthorhombic Pnma symmetry and is made up of zig-zag chains where each silver bromide tetrahedron shares two edges with neighboring tetrahedra. The tetrahedral coordination of silver is retained in CH3NH3Ag2I3, which has monoclinic P21/m symmetry, but the change in stoichiometry leads to a greater degree of edge-sharing connectivity within the silver iodide chains. With band gaps of 3.3 eV (CH3NH3Ag2I3) and 4.0 eV (CH3NH3AgBr2) the absorption onsets of the ternary phases are significantly blue shifted from the binary silver halides, AgBr and AgI, due in part to the decrease in electronic dimensionality. The compounds are stable for at least one month under ambient conditions and are thermally stable up to approximately 200 1C. Density functional theory calculations reveal very narrow valence bands and moderately disperse conduction bands with Ag 5s character. Bond valence calculations are used to analyze the hydrogen bonding between methylammonium cations and coordinatively unsaturated halide ions. The crystal chemistry of these compounds helps to explain the dearth of iodide double perovskites in the literature.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acsearthspacechem.9b00143
