Optically Detected Magnetic Resonance Spectroscopy of Cu-Doped CdSe/CdS and CuInS2 Colloidal Quantum Dots

Solar-Powered Switch of Antiferromagnetism/Ferromagnetism in Flexible Spintronics

The flexible electronics have application prospects in many fields, including as wearable devices and in structural detection. Spintronics possess the merits of a fast response and high integration density, opening up possibilities for various applications. However, the integration of miniaturization on flexible substrates is impeded inevitably due to the high Joule heat from high current density (1012 A/m2). In this study, a prototype flexible spintronic with device antiferromagnetic/ferromagnetic heterojunctions is proposed. The interlayer coupling strength can be obviously altered by sunlight soaking via direct photo-induced electron doping. With the assistance of a small magnetic field (±125 Oe), the almost 180° flip of magnetization is realized. Furthermore, the magnetoresistance changes (15~29%) of flexible spintronics on fingers receiving light illumination are achieved successfully, exhibiting the wearable application potential. Our findings develop flexible spintronic sensors, expanding the vision for the novel generation of photovoltaic/spintronic devices.

Synthesis and hybridization of CuInS2 nanocrystals for emerging applications

Copper indium sulfide (CuInS2) is a ternary A(I)B(III)X(VI)2-type semiconductor featuring a direct bandgap with a high absorption coefficient. In attempts to explore their practical applications, nanoscale CuInS2 has been synthesized with crystal sizes down to the quantum confinement regime. The merits of CuInS2 nanocrystals (NCs) include wide emission tunability, a large Stokes shift, long decay time, and eco-friendliness, making them promising candidates in photoelectronics and photovoltaics. Over the past two decades, advances in wet-chemistry synthesis have achieved rational control over cation-anion reactivity during the preparation of colloidal CuInS2 NCs and post-synthesis cation exchange. The precise nano-synthesis coupled with a series of hybridization strategies has given birth to a library of CuInS2 NCs with highly customizable photophysical properties. This review article focuses on the recent development of CuInS2 NCs enabled by advanced synthetic and hybridization techniques. We show that the state-of-the-art CuInS2 NCs play significant roles in optoelectronic and biomedical applications.

The impact of spatially heterogeneous chemical doping on the electronic properties of CdSe quantum dots: insights from ab initio computation

The introduction of copper (Cu) impurity in semiconductor CdSe quantum dots (QDs) gives rise to unique photoluminescence (PL) bands exhibiting distinctive characteristics, like broad line width, significant Stokes shift, and complex temporal decay. The atomistic origins of these spectral features are yet to be understood comprehensively. We employed multiple computational techniques to systematically study the impact of the spatial heterogeneity of Cu atoms on the stability and photophysical properties, including the emission linewidth of doped QDs under ambient conditions. The Cu substitution introduces a spin-polarized intragap state, the energetic position of which is strongly dependent on the dopant location and causes spectral broadening in QD ensembles. Furthermore, the dopant dynamics under ambient conditions are significantly influenced by the specific arrangement of Cu within the QDs. The dynamic electronic structures of surface-doped CdSe illustrate more pronounced perturbations and vary the mid-gap state position more drastically than those of the core-doped QDs. Vibronic coupling broadens the photoluminescence peaks associated with the conduction band-to-defect level transition for individual QDs. These insights into the dynamic structure-photophysical property relationship suggest viable approaches, such as tuning the operational temperature and selective co-doping, to enhance the functional performances of doped CdSe QDs strategically.

Optically detected magnetic resonance spectroscopic analyses on the role of magnetic ions in colloidal nanocrystals

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.