Light-Emitting Diodes with Cu-Doped Colloidal Quantum Wells: From Ultrapure Green, Tunable Dual-Emission to White Light.

Copper-doped colloidal quantum wells (Cu-CQWs) are considered a new class of optoelectronic materials. To date, the electroluminescence (EL) property of Cu-CQWs has not been revealed. Additionally, it is desirable to achieve ultrapure green, tunable dual-emission and white light to satisfy the various requirement of display and lighting applications. Herein, light-emitting diodes (LEDs) based on colloidal Cu-CQWs are demonstrated. For the 0% Cu-doped concentration, the LED exhibits Commission Internationale de L'Eclairage 1931 coordinates of (0.103, 0.797) with a narrow EL full-wavelength at half-maximum of 12 nm. For the 0.5% Cu-doped concentration, a dual-emission LED is realized. Remarkably, the dual emission can be tuned by manipulating the device engineering. Furthermore, at a high doping concentration of 2.4%, a white LED based on CQWs is developed. With the management of doping concentrations, the color tuning (green, dual-emission to white) is shown. The findings not only show that LEDs with CQWs can exhibit polychromatic emission but also unlock a new direction to develop LEDs by exploiting 2D impurity-doped CQWs that can be further extended to the application of other impurities (e.g., Mn, Ag).

An in vitro study of micromechanics, cellular proliferation and viability on both decellularized porcine dura grafts and native porcine dura grafts.

Damage to the dura mater may occur during intracranial or spinal surgeries, which can result in cerebrospinal fluid leakage and other potentially fatal physiological changes. As a result, biological and synthetic derived scaffolds are typically used to repair dura mater post intracranial or spinal surgeries. The extracellular matrix of xenogeneic dura scaffolds has been shown to exhibit increased cell infiltration and regeneration than synthetic dura materials. In this study, we investigated the biocompatibility of native and decellularized porcine dura by seeding rat fibroblast cells onto the constructs. Cell proliferation, cell viability, and the mechanical properties of these dural grafts were evaluated post-re-seeding on days 3,7 and 14. Live-dead staining and resazurin salts were used to quantify cell viability and cell proliferation, respectively. Micro indentation was conducted to quantify the mechanical integrity of the native and acellular dura graft. The findings indicate that the acellular porcine dura graft creates a beneficial setting for infiltrating rat fibroblast cells. Cell viability, proliferation, and micro indentation results on the acellular grafts are comparable with the native control porcine dura tissue. In conclusion, the porcine scaffold material showed increased cell viability at each time point evaluated. The sustained mechanical response and favorable viability of the cells on the decellularized grafts provide promising insight into the potential use of porcine dura in clinical cranial dura mater graft applications.

Light-Induced Paramagnetism in Colloidal Ag+-Doped CdSe Nanoplatelets.

We describe a study of the magneto-optical properties of Ag+-doped CdSe colloidal nanoplatelets (NPLs) that were grown using a novel doping technique. In this work, we used magnetic circularly polarized luminescence and magnetic circular dichroism spectroscopy to study light-induced magnetism for the first time in 2D solution-processed structures doped with nominally nonmagnetic Ag+ impurities. The excitonic circular polarization (PX) and the exciton Zeeman splitting (ΔEZ) were recorded as a function of the magnetic field (B) and temperature (T). Both ΔEZ and PX have a Brillouin-function-like dependence on B and T, verifying the presence of paramagnetism in Ag+-doped CdSe NPLs. The observed light-induced magnetism is attributed to the transformation of nonmagnetic Ag+ ions into Ag2+, which have a nonzero magnetic moment. This work points to the possibility of incorporating these nanoplatelets into spintronic devices, in which light can be used to control the spin injection.

All-optical control of exciton flow in a colloidal quantum well complex.

Excitonics, an alternative to romising for processing information since semiconductor electronics is rapidly approaching the end of Moore's law. Currently, the development of excitonic devices, where exciton flow is controlled, is mainly focused on electric-field modulation or exciton polaritons in high-Q cavities. Here, we show an all-optical strategy to manipulate the exciton flow in a binary colloidal quantum well complex through mediation of the Förster resonance energy transfer (FRET) by stimulated emission. In the spontaneous emission regime, FRET naturally occurs between a donor and an acceptor. In contrast, upon stronger excitation, the ultrafast consumption of excitons by stimulated emission effectively engineers the excitonic flow from the donors to the acceptors. Specifically, the acceptors' stimulated emission significantly accelerates the exciton flow, while the donors' stimulated emission almost stops this process. On this basis, a FRET-coupled rate equation model is derived to understand the controllable exciton flow using the density of the excited donors and the unexcited acceptors. The results will provide an effective all-optical route for realizing excitonic devices under room temperature operation.

Cd-free Cu-doped ZnInS/ZnS Core/Shell Nanocrystals: Controlled Synthesis And Photophysical Properties.

Here, we report efficient composition-tunable Cu-doped ZnInS/ZnS (core and core/shell) colloidal nanocrystals (CNCs) synthesized by using a colloidal non-injection method. The initial precursors for the synthesis were used in oleate form rather than in powder form, resulting in a nearly defect-free photoluminescence (PL) emission. The change in Zn/In ratio tunes the percentage incorporation of Cu in CNCs. These highly monodisperse Cu-doped ZnInS CNCs having variable Zn/In ratios possess peak emission wavelength tunable from 550 to 650 nm in the visible spectrum. The quantum yield (QY) of these synthesized Cd-free CNCs increases from 6.0 to 65.0% after coating with a ZnS shell. The CNCs possessing emission from a mixed contribution of deep trap and dopant states to only dominant dopant-related Stokes-shifted emission are realized by a careful control of stoichiometric ratio of different reactant precursors during synthesis. The origin of this shift in emission was understood by using steady state and time-resolved fluorescence (TRF) spectroscopy studies. As a proof-of-concept demonstration, these blue excitable Cu-doped ZnInS/ZnS CNCs have been integrated with commercial blue LEDs to generate white-light emission (WLE). The suitable combination of these highly efficient doped CNCs results led to a Commission Internationale de l'Enclairage (CIE) color coordinates of (0.33, 0.31) at a color coordinate temperature (CCT) of 3694 K, with a luminous efficacy of optical radiation (LER) of 170 lm/Wopt and a color rendering index (CRI) of 88.