Core-shell ZnO:Ga-SiO2 nanocrystals: limiting particle agglomeration and increasing luminescence via surface defect passivation

Heat treatment is needed to increase the luminescence intensity of ZnO:Ga particles, but it comes at the cost of higher particle agglomeration. Higher agglomeration results in low transparency of scintillating powder when embedded in a matrix and constitutes one of the biggest disadvantages, besides low light yield and low stopping power, of ZnO:Ga powder. Limiting ZnO:Ga particle size is therefore a key step in order to prepare highly luminescent and transparent composites with prospects for optical applications. In this work, SiO2 coating was successfully used to improve luminescence intensity or limitation of crystallite size growth during further annealing. Furthermore, ZnO:Ga and ZnO:Ga-SiO2 core-shells were embedded in a polystyrene matrix.

Recent progress in two-dimensional inorganic quantum dots

This review critically summarizes recent progress in the categories, synthetic routes, properties, functionalization and applications of 2D materials-based quantum dots (QDs).

Surface Complexed ZnO Quantum Dot for White Light Emission with Controllable Chromaticity and Color Temperature

We report the formation of blue emitting Zn(MSA)₂ complex on the surface of a yellow emitting ZnO quantum dot (Qdot)-out of a complexation reaction between N-methylsalicylaldimine (MSA) and ZnO Qdot. This led to formation of a highly luminescent, photostable, single-component nanocomposite that emits bright natural white light, with (i) chromaticities of (0.31, 0.38) and (0.31, 0.36), (ii) color rendering indices (CRI) of 74 and 82, and (iii) correlated color temperatures (CCT) of 6505 and 6517 K in their solution and solid phases, respectively. Importantly, the control over the chromaticity and CCT-depending upon the degree of complexation-makes the reported nanocomposite a potential new advanced material in fabricating cost-effective single-component white light emitting devices (WLED) of choice and design in the near future.

Significant improvement of near-UV electroluminescence from ZnO quantum dot LEDs via coupling with carbon nanodot surface plasmons

Short-wavelength LEDs, a hot research topic in modern optoelectronics, have attracted tremendous attention in recent years because of their great application potential in both civil and military domains. Compared to conventional metallic surface-plasmons (SPs), carbon nanodot (CD) SPs with less optical loss and low cost, broader SP resonant frequency and good biocompatibility are expected to provide more prominent luminescence enhancement for light emitters. Herein, SP-enhanced near-UV emission quantum dot LEDs (Q-LED) were fabricated via introducing CDs into p-GaN/Al₂O₃/ZnO Q-LEDs by optimizing the molar ratio of ZnO quantum dots to CDs and a significant enhancement (∼20-fold) of the near-UV electroluminescence (EL) intensity from the ZnO-based Q-LEDs was achieved. Time-resolved spectroscopy studies reveal that the observed luminescence enhancement arises due to the resonant coupling between ZnO excitons and CD SPs. The current study not only demonstrates a feasible way to acquire near-UV emission from all-inorganic Q-LEDs, but also provides an effective strategy to enhance the EL intensity of these QD light emitters, which can further be extended to other types of light-emitting devices to improve EL efficiency.

On the influence of Raman scattering of water in the photoluminescence measurement of water dispersed ZnO nanocrystals

We present our investigation on the photoluminescence properties of water dispersed ZnO nanocrystals at various excitation wavelengths, and show that one peak in the emission spectrum (recorded by spectrofluorometer) changes its position when the excitation wavelength is changed. The relationship between the peak position and the excitation wavelength is found to be linear. Recording of the emission spectra (by spectrofluorometer) of water at different excitation wavelengths reveals that the linearly varying peak is present in them as well. It could be recognized that the excitation wavelength dependent peak originates because of Raman scattering of water and it is not intrinsically related to the ZnO nanocrystals. The present work thus highlights the importance of considering Raman scattering of water while interpreting the emission spectrum (recorded by spectrofluorometer) of water dispersed ZnO nanocrystals, which otherwise may lead to misinterpretation such as UV emission and violation of the Kasha's rule, which actually may not be the case.

Abnormal gas pressure sensitivity of the visible emission in ZnO quantum dots prepared by improved sol–gel method: the role of surface polarity

Polar surface induced band bending leads to the abnormal gas pressure sensitivity of visible emission in ZnO quantum dots.

Diverse gatekeepers for mesoporous silica nanoparticle based drug delivery systems

Progress on the design of diverse gatekeepers for mesoporous silica nanoparticle based drug delivery systems is summarized.

Preparation and luminescence properties of ZnO:Ga - polystyrene composite scintillator

Highly luminescent ZnO:Ga-polystyrene composite (ZnO:Ga-PS) with ultrafast subnanosecond decay was prepared by homogeneous embedding the ZnO:Ga scintillating powder into the scintillating organic matrix. The powder was prepared by photo-induced precipitation with subsequent calcination in air and Ar/H₂ atmospheres. The composite was subsequently prepared by mixing the ZnO:Ga powder into the polystyrene (10 wt% fraction of ZnO:Ga) and press compacted to the 1 mm thick pellet. Luminescent spectral and kinetic characteristics of ZnO:Ga were preserved. Radioluminescence spectra corresponded purely to the ZnO:Ga scintillating phase and emission of polystyrene at 300-350 nm was absent. These features suggest the presence of non-radiative energy transfer from polystyrene host towards the ZnO:Ga scintillating phase which is confirmed by the measurement of X-ray excited scintillation decay with picosecond time resolution. It shows an ultrafast rise time below the time resolution of the experiment (18 ps) and a single-exponential decay with the decay time around 500 ps.

Synthesis of poly(n-butyl methacrylate)-(glycidyl methacrylate) block copolymer and its compatibilization at the interface of the QD/epoxy nanocomposite for white LED encapsulation

The QD/epoxy nanocomposite expressed high transparency and luminescence through introducing a poly(BMA-b-GMA) block copolymer as a compatibilizer at the interface between the QD and epoxy matrix.