Semiconductor nanoplatelets (NPLs) have emerged as a very promising class of colloidal nanocrystals for light-emitting devices owing to their quantum-well-like electronic and optical characteristics. However, their lower photoluminescence quantum yield (PLQY) and limited stability have hampered the realization of their outstanding luminescent properties in device applications. Here, to address these deficiencies, we present a two-step synthetic approach that enables the synthesis of core/shell NPLs with precisely controlled shell composition for engineering their excitonic properties. The proposed CdSe colloidal quantum wells possess a graded shell, which is composed of a CdS buffer layer and a Cd x Zn1–x S gradient layer, and exhibit bright emission (PLQY 75–89%) in the red spectral region (634–648 nm) with a narrow emission line width (21 nm). These enhanced optical properties allowed us to attain low thresholds for amplified spontaneous emission (down to ∼40 μJ/cm2) under nanosecond laser excitation. We also studied the electroluminescent performance of these NPLs by fabricating solution-processed light-emitting diodes (LEDs). In comparison to NPL-LEDs with CdSe/CdS core/shell NPLs, which exhibit an external quantum efficiency (EQE) value of only 1.80%, a significantly improved EQE value of 9.92% was obtained using graded-shell NPLs, the highest value for colloidal NPL-based-LEDs. In addition, the low efficiency roll-off characteristics of NPL-LEDs enabled a high brightness of up to ∼46 000 cd/m2 with an electroluminescence peak centered at 650 nm. These findings demonstrate the paramount role that heterostructure engineering occupies in enhancing the optoelectronic characteristics of semiconductor NPLs toward practically relevant levels.

The initial step of particulate growth in a dust forming low pressure radio-frequency discharge has been studied in situ by laser induced particle explosive evaporation (LIPEE). With respect to the conventional light scattering, this method has been found much more efficient to observe small nanometer size particles, especially in the case of UV excimer laser radiation. Experimental results interpreted by a simple model of laser-particle interaction show that the intensity of LIPEE continuum emission depends on the particle radius roughly as r4. This interaction is essentially different from Rayleigh scattering, as the latter varies as r6. A study of time evolution of powder formation by LIPEE emission reveals the initial formation of nanometer size crystallites and the coalescence process leading to larger scale particles. It could be demonstrated that the critical step of dust formation is the initial clustering process leading to nanometer scale crystallites.

Cesius lead halide perovskite colloidal nanocrystals are among the most promising perovskite systems for light emitting devices applications, due to their high fluorescence quantum yield and high optical gain at room temperature. In this Letter, we report on the first investigation of the temperature dependence of the Amplified Spontaneous Emission (ASE) properties of thin films of CsPbBr 3 nanocrystals. We demonstrate that ASE is strongly temperature dependent, with a complex variation in temperature of the ASE intensity, threshold, and peak wavelength. The joint investigation of the photoluminescence (PL) spectra below and above the ASE threshold allows us to conclude that the temperature increase results in the formation of disordered sub-domains emitting in the low energy tail of the PL spectra, leading to the existence of three emission regimes with transitions at about 90 K and about 170 K, with individually different temperature dependences.

Metal halide perovskites are currently emerging as highly promising optoelectronic materials. It has been recently demonstrated that fully inorganic solution processed CsPbBr3 perovskite thin films show good electroluminescence properties combined with high thermal stability. In this work, we investigate in details the amplified spontaneous emission (ASE) properties of CsPbBr3 perovskite thin films, as a function of the temperature and the trap density, modified by changing the CsBr–PbBr2 precursor concentration. ASE is observed in samples from both CsBr-rich solution (low trap density) and equimolar solution (higher trap density), up to about 150 K, with a minimum threshold of 26 and 29 μJ cm–2 at 10 K, respectively. However, the different distribution of defect states, mainly above the first exciton level in the former and below it in the latter, strongly improved optical gain at 10 K and changed the ASE temperature dependence of CsBr-rich films.

The use of lead halide perovskites in optoelectronic and photonic devices is mainly limited by insufficient long-term stability of these materials. This issue is receiving growing attention, mainly owing to the operational stability improvement of lead halide perosvkites solar cells. On the contrary, fewer efforts are devoted to the stability improvement of light amplification and lasing. In this report we demonstrate that a simple hydrophobic functionalization of the substrates with hexamethyldisilazane (HMDS) allows to strongly improve the Amplified Spontaneous Emission (ASE) properties of drop cast CsPbBr3 nanocrystal (NC) thin films. In particular we observe an ASE threshold decrease down to 45% of the value without treatment, an optical gain increase of up to 1.5 times and an ASE operational stability increase of up to 14 times. These results are ascribed to a closer NC packing in the films on HMDS treated substrate, allowing an improved energy transfer towards the larger NCs within the NC ensemble, and to the reduction of the film interaction with moisture. Our results propose hydrophobic functionalization of the substrates as an easy approach to lower the ASE and lasing thresholds, while simultaneously increasing the active material stability.

Extraction of negative ions from pulsed electronegative capacitively coupled plasmas J. Appl. Phys. 112, 033303 (2012) High electronegativity multi-dipolar electron cyclotron resonance plasma source for etching by negative ions J. Appl. Phys. 111, 083303 (2012) Decreasing high ion energy during transition in pulsed inductively coupled plasmas Appl. Phys. Lett. 100, 044105 (2012) Characterization and mechanism of He plasma pretreatment of nanoscale polymer masks for improved pattern transfer fidelity Appl. Phys. Lett. 99, 261501 (2011) Origin of electrical signals for plasma etching endpoint detection Time-and space-resolved emission and laser-induced fluorescence spectroscopic measurements were performed to investigate vaporization and plasma formation resulting from excimer laser irradiation of titanium targets in a low-pressure nitrogen atmosphere. Measurement series have been done by varying the laser intensity from the vaporization threshold at 25 MW crne2 up to values of about 500 MW cm-" typically applied in pulsed laser deposition processing of titanium nitride films. Thus, the transition from thermal evaporation to the high-density plasma formation process, leading to the production of reactive species and high-energy ions, was evidenced. An interesting result for the comprehension of the reactive deposition process was the observation of a quantity of dissociated and ionized nitrogen, which is transported with the plasma front in the direction of the substrate. 0 199.5 American Institute of Physics.

Lead halide perovskites are currently receiving increasing attention due to their potential to combine easy active layers fabrication, tunable electronic and optical properties with promising performance of optoelectronic and photonic device prototypes. In this paper, we review the main development steps and the current state of the art of the research on lead halide perovskites amplified spontaneous emission and on optically pumped lasers exploiting them as active materials.

The widespread use of nanoparticles (NPs) in medical devices has opened a new scenario in the treatment and prevention of many diseases and infections owing to unique physico-chemical properties of NPs. In this way, silver nanoparticles (AgNPs) are known to have a strong antimicrobial activity, even at low concentrations, due to their ability to selectively destroy cellular membranes. In particular, in the field of dental medicine, the use of AgNPs in different kinds of dental prosthesis matrixes could be a fundamental tool in immunodepressed patients that suffer of different oral infections. Candida albicans (C. albicans), an opportunistic pathogenic yeast with high colonization ability, is one of the causative agents of oral cavity infection. In our work, we added monodispersed citrate-capping AgNPs with a size of 20 nm at two concentrations (3 wt% and 3.5 wt%) in poly(methyl methacrylate) (PMMA), the common resin used to develop dental prostheses. After AgNPs characterization, we evaluated the topographical modification of PMMA and PMMA with the addition of AgNPs by means of atomic force microscopy (AFM), showing the reduction of surface roughness. The C. albicans colonization on PMMA surfaces was assessed by the Miles and Misra technique as well as by scanning electron microscopy (SEM) at 24 h and 48 h with encouraging results on the reduction of yeast viability after AgNPs exposure.