Two-dimensional (2D) semiconductors are attractive candidates for a variety of optoelectronic applications owing to the unique electronic properties that arise from quantum confinement along a single dimension. Incorporating nonradiative mechanisms that enable directed migration of bound charge carriers, such as Förster resonance energy transfer (FRET), could boost device efficiencies provided that FRET rates outpace undesired relaxation pathways. However, predictive models for FRET between distinct 2D states are lacking, particularly with respect to the distance d between a donor and acceptor. We approach FRET in systems with binary mixtures of donor and acceptor 2D perovskite quantum wells (PQWs), and we synthetically tune distances between donor and acceptor by varying alkylammonium spacer cation lengths. FRET rates are monitored using transient absorption spectroscopy and ultrafast photoluminescence, revealing rapid picosecond lifetimes that scale with spacer cation length. We theoretically model these binary mixtures of PQWs, describing the emitters as classical oscillating dipoles. We find agreement with our empirical lifetimes and then determine the effects of lateral extent and layer thickness, establishing fundamental principles for FRET in 2D materials.

Copper (I) iodide hybrids are of interest for next-generation lighting technologies because of their efficient luminescence in the absence of rare-earths. Here, we report ten structurally diverse hybrid copper (I) iodides that emit in the green-red region with quantum yields reaching 67 %. The compounds display a diversity of structures including ones with 1D Cu-1 chains, Cu2I2 rhomboid dimers, and structures with two different arrangements of Cu4I4 tetramers. The compounds with Cu2I2 rhomboid dimers or Cu4I4 cubane tetramer have higher photoluminescence quantum yield than those with Cu-I 1D chain and octahedral Cu4I4 tetramer, owing to the optimal degree of condensation of the inorganic motifs that suppresses non-radiative processes. Electronic structure calculations on these compounds point out the critical influence of the inorganic motif and organic ligand on the nature of the band gaps and thus the excitation characteristics. Temperature dependent photoluminescence spectra are presented to better understand the nature of luminescence in compounds with different inorganic motifs. The emerging understanding of composition-structure-property correlations in this family provide inspiration for the rational design of hybrid phosphors for general lighting applications.

Metal nitrides are a promising non-toxic, inexpensive, and durable material for photothermal applications. The photothermal properties of titanium nitride are measured using time-resolved X-ray diffraction following optical excitation.