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.

No abstract

Erbium doped Al 2 O 3 films with concentrations up to 6ϫ10 20 Er cm Ϫ3 have been prepared in a single step process by pulsed-laser deposition. Alternate ablation of Al 2 O 3 and Er targets has been used to control the in-depth distribution and in-plane concentration of Er 3ϩ ions independently. The characteristic Er 3ϩ photoluminescence response at 1.53 m has been studied as a function of the Er 3ϩ distribution. It is found that lifetime values can be greatly increased by increasing the Er 3ϩ-Er 3ϩ in-depth separation above 3 nm. This result can be related to a reduced Er 3ϩ-Er 3ϩ energy migration process. The in-plane Er 3ϩ concentration was increased by either increasing the number of pulses on the Er target or the laser energy density for ablation. By the latter method in-plane concentrations as high as 1.1ϫ10 14 Er cm Ϫ2 per layer ͑corresponding to 2 ϫ10 20 Er cm Ϫ3 ͒ were achieved, while keeping lifetime values as high as 6 ms. This result is explained in terms of shallow Er 3ϩ implantation during deposition.

RésuméLes vermiculites Mg, Ca, Sr et Ba ont été étudiées par diffraction des rayons X et absorption infra-rouge.Pour les vermiculites monocouches, l'espacement interréticulaire est compris entre 12·2 et 11·45 Å.On distingue: (i) les vermiculites Ba; le cation, entouré de 5 à 6 molécules d'eau, est à environ 1Å du plan médian et il intéragit avec un hydroxyle structural du feuillet le plus proche, (ii) les vermiculites Mg, Ca et Sr; le cation, entrouré de 3 ou 4 molécules d'eau,est dans le plan médian ou dans son voisinage (0·3 Å), et il n'interagit pas avec les hydroxyles des feuillets.Pour les vermiculites anhydres, l'espacement interréticulaire est inférieur à 10 Å, le cation est dans le plan médian et il intéragit avec les hydroxyles de 2 feuillets opposés.A partir de ces résultats, complétés par les données de la bibliographie, des modéles sont proposés pour représenter l'organisation de l'espace interlamellaire.

CVD boron nitride films have been deposited at 800 °C from diborane, ammonia, and hydrogen gas mixtures, using different B2H6 flow rates. The effect of the [B2H6]/[NH3] ratio in the gas mixture on the structure, composition, and the stability of the layers in humid atmospheres has been studied. For low [B2H6]/[NH3] ratios (r ≤ 0.25), the deposition rate is low and some crystalline ordering in the deposit was detected. However, when ratios >0.25 are used, stable amorphous boron nitride films are deposited at deposition rates four times higher (160 nm min-1). The partially turbostratic boron nitride films, deposited at r ≤ 0.25, are unstable in humid atmospheres (80% moisture). The evolution of the unstable films was followed by infrared spectroscopy. It is observed that the turbostratic component in the film is rapidly attacked by the water molecules present in the atmosphere, giving rise finally to boron enrichment in the films. After this stage, the attack rate becomes slower, due to the higher stability of the amorphous component in the films.