Ultrahigh-quality (Q) factor microresonators have a lot of applications in the photonics domain ranging from low-threshold nonlinear optics to integrated optical sensors. Glass-based whispering gallery mode (WGM) microresonators are easy to produce by melting techniques, however they suffer from surface contamination which limits their long-term quality factor to a few 108. Here we show that an optical gain provided by erbium ions can compensate for residual losses. Moreover it is possible to control the coupling regime of an ultrahigh Q-factor three port microresonator from undercoupling to spectral selective amplification by changing the pumping rate. The optical characterization method is based on frequency-swept cavity-ring-down-spectroscopy. This method allows the transmission and dispersive properties of perfectly transparent microresonators and intrinsic finesses up to 4.0 × 107 to be measured. Finally we characterize a critically coupled fluoride glass WGM microresonator with a diameter of 220 μm and a loaded Q-factor of 5.3 × 109 is demonstrated.

A series of samples based on poly(3-hydroxybutyrate) (PHB) containing five different additives were prepared and their thermal stability and flammability were discussed. The samples first underwent flammability screening by using Pyrolysis Combustion Flow Calorimeter (PCFC) analyses. Then, four samples were selected for further investigations. PHB composites containing sepiolite (Sep.) inorganic nanofiller, and also organic ammonium polyphosphate (APP) were examined for flammability and thermal behavior using PCFC, thermogravimetric analysis (TGA), flame test, and Differential Scanning Calorimetry (DSC) analyses. Moreover, burning behavior of samples were captured on a digital camera to give a deeper sense of their flammability character for comparison. The results revealed a significant improvement of flammability and thermal stability of composites, particularly in the presence of sepiolite with respect to the value obtained for unfilled PHB. Regarding TGA results, the char residue yield was increased to ca. 20.0 wt.% in the presence of sepiolite, while 0.0 wt.% was observed for PHB. PCFC measurements uncovered higher performance of PHB-Sep. sample as signaled by 40% reduction in the peak of heat release rate with respect to PHB. According to observations, PHB-Sep. sample showed non-dripping behavior with high capacity of charring in the presence of Sep. in a vertical flame test.

Natural terpenes such as linalool (L), geraniol (G), and geranyl acetate (GA), from 10 to 20 wt %, were compounded with poly­(3-hydroxybutyrate) (PHB) to assess the influence of the content of these biobased molecules on the structural and mechanical properties of PHB. Differential scanning calorimetry (DSC) measurements showed a decrease of T g from 8.5 °C to −13 °C, showing the plasticization effect of the terpenes. This effect is correlated with the decrease of the crystallinity degree from 57 to 36%. Moreover, tensile tests were conducted on PHB-containing terpenic plasticizers. The increase of the elongation at the break of the plasticized PHB over 650% combined with a decrease of the Young’s modulus with regard to pure PHB were obtained in the presence of 20 wt % of geranyl acetate. Dynamical mechanical analysis also revealed that the use of terpenes as additives promoted the decrease of E′ and the glass transition temperature. The effect is more pronounced with geranyl acetate due to the presence of the segment bearing an ester group that increases free volume and molecular mobility. Among the different plasticizers used here, the addition of geranyl acetate is an attractive way to obtain soft PHB from renewable additives.

The synthesis and spectroscopic investigation of Pr(3+):YF(3) nanoparticles with nominal concentration between 0.05% and 5 at% Pr(3+) are reported. Pr(3+) emission in the visible range of the spectrum is investigated at room temperature and at 10 K as well as time resolved spectroscopy as a function of Pr(3+) concentration. The upconverted emission from the orange to the blue region is observed and the time-resolved spectroscopy of the visible emissions is discussed as a function of the doping level. A careful analysis of the decays permits identification of the main energy-transfer mechanisms that determine the population of the excited levels at various times during the decay.

The synthesis of TBA-DASA-POM-DASA,t he first photoactive covalenth ybrid polyoxometalate (POM)i ncorporatingadonor-acceptor Stenhouse adduct (DASA) reverse photochrome, is presented. It has been evidenced that in solution the equilibrium between the colorless cyclopentenone and the highly colored triene conformers is strongly dependent not only on the nature of the solventb ut also the countercations, allowing to tune its optical properties. This complex has been further associated to photochromic spironaphtoxazinec ations,r esulting in am aterial which can be activated by two distinct optical stimuli. Moreover, when combined with N-methyldiethanolamine, TBA-DASA-POM-DASA constitutes ap erforming photoinitiating system for polyethylene glycol diacrylatep olymerization and under visible light irradiation, ap romising result in ad omain scarcely developed in POM chemistry.[b] L. Michely,Dr. D.-

Thanks to its remarkable properties such as sustainability, compostability, biocompatibility, and transparency, poly-Llactic acid (PLA) would be a suitable replacement for oil-based polymers should it not suffer from low flexibility and poor toughness, restricting its use to rigid plastic by excluding elastomeric applications. Indeed, there are few fully biobased and biodegradable transparent elastomers−PLA-based or not−currently available. In the last decades, many strategies have been investigated to soften PLA and enhance its toughness and elongation at break by using plasticizers, oligomers, or polymers. This work shows how a ferulic acid-derived biobased additive (BDF) blends with a common rigid and brittle commercial grade of polylactic acid to provide a transparent non-covalently cross-linked elastomeric material with shape memory behavior exhibiting an elongation at break of 434% (vs 6% for pristine PLA). Through a structure−activity relationship analysis conducted with BDF analogues and a modeling study, we propose a mechanism based on π−π stacking to account for the elastomeric properties. Blending ferulic acid derivatives with polylactic acid generates a new family of fully sustainable transparent elastomeric materials with functional properties such as shape memory.

A series of acetyl pyrenes and pyrenyl ynones with and without tert‐butyl groups showed distinct mechanofluorochromism (MFC). Four pairs of polymorphic solids were found out of six compounds and interestingly, each of them showed hypsochromic, bathochromic or off‐to‐on MFC. The MFC properties were rationalized by categorizing the packing schemes into herringbone, sandwich, beta and gamma motifs depending on the relative contributions of C⋅⋅⋅C (or π‐π) against C⋅⋅⋅H contacts. The bulky tert‐butyl and trimethylsilyl groups served not only to reduce the number of aggregation patterns but also to prohibit the complete back reactions in solid state. Our results suggest that the simple pyrene derivatives may be promising candidates for a novel group of mechanically‐sensitive materials.

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