A multidisciplinary approach for the production and characterization of colloidal quantum dots, which show great promise for implementation in modern optoelectronic applications, is described. The approach includes the design and formation of unique core/shell structures with alloy-composed layers between the core and the shell. Such structures eliminate interfacial defects and suppress the Auger process, thus reducing the known fluorescence blinking and endowing the quantum dots with robust chemical and spectral stability. The unique design enables the generation and sustained existence of single and multiple excitons with a defined spin-polarized emission recombination. The studies described herein implement the use of single-dot magneto-optical measurements and optically detected magnetic resonance spectroscopy, for direct identification of interfacial defects and for resolving exciton fine structure. The results are of paramount importance for a fundamental understanding of optical transitions in colloidal quantum dots, with an impact on appropriate materials design for practical applications.

Controlling the spin degrees of freedom of photogenerated species in semiconductor nanostructures via magnetic doping is an emerging scientific field that may play an important role in the development of new spinbased technologies. The current work explores spin properties in colloidal CdSe/ CdS:Mn seeded-nanorod structures doped with a dilute concentration of Mn 2+ ions across the rods. The spin properties were determined using continuous-wave optically detected magnetic resonance (ODMR) spectroscopy recorded under variable microwave chopping frequencies. These experiments enabled the deconvolution of a few different radiative recombination processes: band-toband, trap-to-band, and trap-to-trap emission. The results uncovered the major role of carrier trapping on the spin properties of elongated structures. The magnetic parameters, determined through spin-Hamiltonian simulation of the steady-state ODMR spectra, reflect anisotropy associated with carrier trapping at the seed/rod interface. These observations unveiled changes in the carriers' gfactors and spin-exchange coupling constants as well as extension of radiative and spin−lattice relaxation times due to magnetic coupling between interface carriers and neighboring Mn 2+ ions. Overall, this work highlights that the spin degrees of freedom in seeded nanorods are governed by interfacial trapping and can be further manipulated by magnetic doping. These results provide insights into anisotropic nanostructure spin properties relevant to future spin-based technologies.

The low-temperature colloidal production of II−VI nanoplatelet heterostructures has stimulated the interest of researchers due to the possible uses of these materials in various optoelectronic devices. Here, we report a roomtemperature coating by CdS or ZnS dots of preprepared CdSe nanoplatelets. The dot coating process made use of a synthesis developed for the formation of freestanding CdS and ZnS species, involving injection of a metal precursor into reactive sulfur−amine solutions at room temperature. CdSe structured nanoplatelets with 1.75 nm thickness were used as the core constituent. The structural properties were investigated using Fourier transform infrared spectroscopy and advanced electron microscopy, while the elemental mapping was verified using high-angle annular dark field transmission electron microscopy. The results showed a dots-on-plate structure, resembling an intermediate configuration between core/crown or core/shell heterostructures. A thorough study of optical properties demonstrated a dramatic spectral shift of the absorption edge to lower energies, regardless of the uniformity of the coating layer, maintaining spectral stability over two months while stored at ambient conditions. Other optical measurements included examination of temperature-dependent photoluminescence and transient photoluminescence decay, from room temperature down to ∼4 K. These measurements revealed excitons, trions, and trapped carrier recombination emission with variable relative intensities following the temperature change. The dots-on-plate structures studied displayed a short photoluminescence decay (≤nanosecond), compatible with that of core/shell (crown) structures prepared at high temperatures. As a result, the presented techniques are alternative pathways that eliminate the requirement for excessive temperatures and/or multistep processes, instead providing rapid, inexpensive, and scalable procedures with practical advantages.

Magnetic doping in halide perovskite semiconductors is of timely interest in the pursuit of new optical and magnetic properties that surpass those of the existing undoped materials. Here, we report a thorough investigation of the optical and magneto-optical properties of Ni 2+ -doped cesium lead halide perovskite with a chemical formula CsPb(Br 1−x Cl x ) 3 , implementing steady-state and transient photoluminescence (PL), polarized magneto-PL, and optically detected magnetic resonance (ODMR) spectroscopies. The magneto-PL measurements revealed three PL features with different degrees of circular polarization, associated with recombination from band-edge and trapping states. The ODMR measurements probed magnetic resonance transitions of photogenerated electrons and holes with phenomenological g-factors that deviate from those of band-edge states. Simulations of the ODMR spectra suggested carriers' trapping in shallow traps with a slight anisotropic surrounding and with weak electron−hole exchange coupling. Furthermore, we observed substantial broadening of the hole resonance, due to its spin-exchange coupling with the Ni 2+ unpaired spins. Overall, these ODMR measurements uncovered the role of the dopant in localizing photogenerated carriers by stiffening (becoming more rigid by decreasing the structural dynamics) the crystal structure and, for the first time, provide a direct observation of carrier-dopant spin exchange interactions in metal-halide perovskite nanocrystals. These results offer insight into the influence of magnetic dopants on the electronic structures of metal-halide perovskites, with a view toward emerging spin-based devices made from perovskites.

Incorporating magnetic ions into semiconductor nanocrystals has emerged as a prominent research field for manipulating spin-related properties. The magnetic ions within the host semiconductor experience spin-exchange interactions with photogenerated carriers and are often involved in the recombination routes, stimulating special magneto-optical effects. The current account presents a comparative study, emphasizing the impact of engineering nanostructures and selecting magnetic ions in shaping carrier–magnetic ion interactions. Various host materials, including the II–VI group, halide perovskites, and I–III–VI2 in diverse structural configurations such as core/shell quantum dots, seeded nanorods, and nanoplatelets, incorporated with magnetic ions such as Mn2+, Ni2+, and Cu1+/2+ are highlighted. These materials have recently been investigated by us using state-of-the-art steady-state and transient optically detected magnetic resonance (ODMR) spectroscopy to explore individual spin-dynamics between the photogenerated carriers and magnetic ions and their dependence on morphology, location, crystal composition, and type of the magnetic ion. The information extracted from the analyses of the ODMR spectra in those studies exposes fundamental physical parameters, such as g-factors, exchange coupling constants, and hyperfine interactions, together providing insights into the nature of the carrier (electron, hole, dopant), its local surroundings (isotropic/anisotropic), and spin dynamics. The findings illuminate the importance of ODMR spectroscopy in advancing our understanding of the role of magnetic ions in semiconductor nanocrystals and offer valuable knowledge for designing magnetic materials intended for various spin-related technologies.