Targeted Delivery System Based on Magnetic Mesoporous Silica Nanocomposites with Light-Controlled Release Character

We report the facile synthesis and easy operation of a smart delivery system based on core–shell structured magnetic mesoporous silica nanocomposites covalently grafted with light-responsive azobenzene derivatives, which integrates magnetic targeting and stimuli-responsive release property. Irradiation with visible light triggers the release of guest molecules loaded in the mesopores

Fast Photoconductive Responses in Organometal Halide Perovskite Photodetectors

Inorganic semiconductor-based photodetectors have been suffering from slow response speeds, which are caused by the persistent photoconductivity of semiconductor materials. For realizing high speed optoelectronic devices, the organometal halide perovskite thin films were applied onto the interdigitated (IDT) patterned Au electrodes, and symmetrical structured photoconductive detectors were achieved. The detectors were sensitive to the incident light signals, and the photocurrents of the devices were 2–3 orders of magnitude higher than dark currents. The responsivities of the devices could reach up to 55 mA W^1–. Most importantly, the detectors have a fast response time of less than 20 μs. The light and bias induced dipole rearrangement in organometal perovskite thin films has resulted in the instability of photocurrents, and Ag nanowires could quicken the process of dipole alignment and stabilize the photocurrents of the devices

Blue-Emitting K₂Al₂B₂O₇:Eu²⁺ Phosphor with High Thermal Stability and High Color Purity for Near-UV-Pumped White Light-Emitting Diodes

Novel blue-emitting K₂Al₂B₂O₇:Eu²⁺ (KAB:Eu²⁺) phosphor was synthesized by solid state reaction. The crystal structural and photoluminescence (PL) properties of KAB:Eu²⁺ phosphor, as well as its thermal properties of the photoluminescence, were investigated. The KAB:Eu²⁺ phosphor exhibits broad excitation spectra ranging from 230 to 420 nm, and an intense asymmetric blue emission band centered at 450 nm under λ_ex = 325 nm. Two different Eu²⁺ emission centers in KAB:Eu²⁺ phosphor were confirmed via their fluorescence decay lifetimes. The optimal concentration of Eu²⁺ ions in K_2–<i>x</i>Eu_<i>x</i>Al₂B₂O₇ was determined to be <i>x</i> = 0.04 (2 mol %), and the corresponding concentration quenching mechanism was verified to be the electric dipole–dipole interactions. The PL intensity of the nonoptimized KAB:0.04Eu²⁺ phosphor was measured to be ∼58% that of the commercial blue-emitting BaMgAl₁₀O₁₇:Eu²⁺ phosphor, and this phosphor has high color purity with the CIE coordinate (0.147, 0.051). When heated up to 150 °C, the KAB:0.04Eu²⁺ phosphor still has 82% of the initial PL intensity at room temperature, indicating its high thermal stability. These results suggest that the KAB:Eu²⁺ is a promising candidate as a blue-emitting n-UV convertible phosphor for application in white light emitting diodes

Size- and Composition-Dependent Energy Transfer from Charge Transporting Materials to ZnCuInS Quantum Dots

We studied the energy transfer processes from organic charge transporting materials (CTMs) to ZnCuInS (ZCIS) quantum dots (QDs) with different emission wavelength by steady-state and time-resolved photoluminescence (PL) spectroscopy. The change in the PL excitation intensity of the ZCIS QDs and the PL decay time of the CTMs clearly demonstrated an efficient energy transfer process in the ZCIS/CTM blend films. It was found that the efficiency of Förster resonance energy transfer significantly increases with increasing the particle size and decreasing the Zn content in the QDs, which is well consistent with the estimated Förster radii (<i>R</i>₀) varying from 3 to 5 nm. In addition, the PL quenching of the QDs related to the charge separation process was also observed in some of the samples. The energy transfer and charge separation processes in the films were well explained based on the band alignment between the ZCIS QDs and CTMs

The Inductive Effect of Neighboring Cations in Tuning Luminescence Properties of the Solid Solution Phosphors

Forming solid solutions through cation substitution is an efficient way to improve the luminescence properties of Ce³⁺ or Eu²⁺ activated phosphors and even to develop new ones, which is badly needed for phosphor-converted white LEDs. Here, we report new color tunable solid solution phosphors based on Eu²⁺ activated K₂Al₂B₂O₇ as a typical case to demonstrate that, besides crystal field splitting of 5<i>d</i> levels, centroid shift and Stokes shift can be dominant in tuning excitation and emission spectra as well as thermal stability of solid solution phosphors, both of which were previously considered to be negligible. Moreover, a general model involving the inductive effect of neighboring cations is proposed to explain the obvious variations in centroid shift and Stokes shift with cation substitution. Our work is propitious for the construction of more reasonable structure–property relations and thus offers theoretical guidance for designing solid solution phosphors

Photoinduced Charge Separation and Recombination Processes in CdSe Quantum Dot and Graphene Oxide Composites with Methylene Blue as Linker

The charge separation and recombination processes between CdSe quantum dot (QD) and graphene oxide (GO) composites with linking molecule methylene blue (MB⁺) were studied by femtosecond transient absorption spectroscopy. Anchoring MB⁺ molecules on GO results in significant changes in steady-state and transient absorption spectra, where the exciton dissociation time in the CdSe QD-MB⁺-GO composite was determined to be 1.8 ps. Surprisingly, the ground state bleaching signal increased for MB⁺-GO complex was found to be 5.2 ps, in relation with electron transfer from QD to GO. On the other hand, the strong electronic coupling between MB<b>^•</b>-GO radical and GO prolonged charge recombination process (≥5 ns) in QD-MB⁺-GO composites. Charge separation and recombination processes at the interface between semiconductor QDs and graphene can thus be modulated by the functionalized dye molecules

Photoinduced Charge Separation and Recombination Processes in CdSe Quantum Dot and Graphene Oxide Composites with Methylene Blue as Linker

The charge separation and recombination processes between CdSe quantum dot (QD) and graphene oxide (GO) composites with linking molecule methylene blue (MB⁺) were studied by femtosecond transient absorption spectroscopy. Anchoring MB⁺ molecules on GO results in significant changes in steady-state and transient absorption spectra, where the exciton dissociation time in the CdSe QD-MB⁺-GO composite was determined to be 1.8 ps. Surprisingly, the ground state bleaching signal increased for MB⁺-GO complex was found to be 5.2 ps, in relation with electron transfer from QD to GO. On the other hand, the strong electronic coupling between MB<b>^•</b>-GO radical and GO prolonged charge recombination process (≥5 ns) in QD-MB⁺-GO composites. Charge separation and recombination processes at the interface between semiconductor QDs and graphene can thus be modulated by the functionalized dye molecules

High-Performance Organic Small-Molecule Panchromatic Photodetectors

High-performance panchromatic organic photodetectors (OPDs) containing small molecules lead phthalocyanine (PbPc) and C₇₀ fullerene as donor and acceptor, respectively, were demonstrated. The OPDs had either a PbPc/C₇₀ planar heterojunction (PHJ) or a PbPc/PbPc:C₇₀/C₇₀ hybrid planar-mixed molecular heterojunction (PM-HJ) structure. Both the PHJ and the PM-HJ devices showed a broad-band response that covered wavelengths from 300 to 1100 nm. An external quantum efficiency (EQE) higher than 10% and detectivity on the order of 10¹² Jones were obtained in the wavelength region from 400 to 900 nm for the PHJ device. The EQE in the near-infrared region was enhanced by using the PM-HJ device structure, and a maximum EQE of 30.2% at 890 nm was observed for the optimized device with a 5% PbPc-doped C₇₀ layer. Such an EQE is the highest at this wavelength of reported OPDs. The detectivity of the PM-HJ devices was also higher than that of the PHJ one, which is attributed to the increased efficiency of exciton dissociation in bulk heterojunction structure, increased absorption efficiency caused by formation of triclinic PbPc in the PbPc:C₇₀ mixed film when it was deposited on a pristine PbPc layer, and high hole mobility of the PbPc-doped C₇₀ layer