Abstract

Amongst the different optoelectronic applications of conjugated polymers, the development of new active materials for optically pumped organic lasers is still an open question particularly in the blue-near UV spectral range. We investigate the emission properties of poly[(9,9-dioctylfluorene-2,7-dyil)- alt-p-phenylene] (PFP) neat films under nanosecond pump. We demonstrate that thanks to the introduction of a phenylene moiety between two fluorene units it is possible to obtain Amplified Spontaneous Emission (ASE) with a lower threshold and a blue shifted wavelength with respect to poly(9,9-dioctylfluorene) (PFO). We demonstrate efficient ASE with a minimum threshold as low as 23 μJcm−2 and a minimum ASE wavelength of 436 nm. A maximum net optical gain of about 26 cm−1 is measured at an excitation density of 0.23 mJcm−2. These results make the PFP a good active material for optically pumped deep blue organic lasers.

Natural dyes have been used extensively in the past for many purposes, such us to colour fibers and to produce inks, watercolours and paints, but their use declined rapidly after the discovery of synthetic colours. Nowadays we witness a renewed interest, as natural dyes are neither toxic nor polluting. In this work, physical and chemical properties of four selected dyes, namely red (Madder), yellow (Weld and Turmeric) and blue (Woad) colours, produced by means of traditional techniques at the Museo dei Colori Naturali (Lamoli, Italy), have been investigated. The chromatic properties have been studied through the reflectance spectroscopy, a non-invasive technique for the characterisation of chromaticity. Reflection spectra both from powders and egg-yolk tempera models have been acquired to provide the typical features of the dyes in the UVvis spectral range. Moreover, to assess the feasibility of laser cleaning procedures, tempera layers were investigated after irradiation with an excimer laser. Micro Raman spectroscopy, Scanning Electron Microscopy and Energy Dispersive X-Ray analyses have complemented the survey, returning compositional and morphological information as well.

LY2157299 (LY), which is very small molecule bringing high cancer diffusion, is a pathway antagonist against TGFβ. LY dosage can be diluted by blood plasma, can be captured by immune system or it might be dissolved during digestion in gastrointestinal tract. The aim of our study is to optimize a "nano-elastic" carrier to avoid acidic pH of gastrointestinal tract, colon alkaline pH, and anti-immune recognition. Polygalacturonic acid (PgA) is not degradable in the gastrointestinal tract due to its insolubility at acidic pH. To avoid PgA solubility in the colon, we have designed its conjugation with Polyacrylic acid (PAA). PgA-PAA conjugation has enhanced their potential use for oral and injected dosage. Following these pre-requisites, novel polymeric nano-micelles derived from PgA-PAA conjugation and loading LY2157299 are developed and characterized. Efficacy, uptake and targeting against a hepatocellular carcinoma cell line (HLF) have also been demonstrated.

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 temperature dependence of amplified spontaneous emission (ASE) properties of thin films of CsPbBr3 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 subdomains emitting in the low-energy tail of the PL spectra, leading to the existence of three emission regimes with transitions at about 90 and 170 K, with individually different temperature dependences.

In this work, the deposition of Y thin films by laser beams with 0.5 ps and 5 ps pulse durations at different laser fluences (1.2-6.4 J/cm(2)) is reported. The morphology of the deposited films and of the ablated target surface is investigated by scanning electron microscopy analyses. The present results show that the films, well adherent to the substrates, are characterized by a high abundance of sub-micrometric particulates with average size less than 0.3 mu m, whose density decreases with increasing laser fluence. The formation of columnar structures observed on the target surface seems to be responsible of the poor film homogeneity. Acceptable deposition rate in the range of 0.08-0.16 A/pulse with 5 ps pulse duration is found; on the contrary with 0.5 ps pulse duration, it is not possible to get information on deposition rate as a function of the laser fluence due to the high non-uniformity of the films. A comparison with the results previously obtained in ns regime is presented and discussed. The achievements of our investigation will be useful to optimize the synthesis of photocathodes based on Y films for the production of bright electron beams in radio-frequency photoinjectors.