No abstract

relatively cheap, extremely lightweight and compact, and are pretty rugged with a long usable life span. Besides, these solid-state sources generate less heat and require less power compared with more traditional light sources. Among these new materials, cesium lead halide (CsPbX 3 ) perovskite nanocrystals (NCs) are excellent candidates for emerging optoelectronic devices [1][2][3][4] due to their low cost, scalable synthesis, high photoluminescence (PL) quantum yield, and tunability along all the visible range varying their composition and size. [3,[5][6][7] Inorganic perovskite NCs present narrow emission bands and good stability to environmental conditions. Moreover, these NCs are pretty versatile, and they can be embedded within organic and inorganic matrices, such as polymethyl methacrylate, [7] or silica [8] for improved stability. [4] In order to harness and control the emission from the cesium lead halide (CsPbX 3 ) nanocrystals, they are often accompanied by a light managing scheme that enhances the PL [9,10] or provides emission directionality. [11] It is also possible to directly shape the perovskite NCs themselves into photonic architectures such as thin films, [12] 2D gratings, [13] microdisks, [14] nanowires, [15,16] 3D photonic crystals, [17,18] or l micro hemispheres, [19] among others. Even though this material is suitable for many optoelectronic devices, its toxicity and instability against oxidation and humidity limit their potential into potentially commercial applications. The encapsulation of these NCs into transparent oxides has proved to be a solution to improve their photonic stability as well as to reduce the metal halide toxicity, leaving the luminescent properties reasonably unmodified. Different strategies of encapsulation have been recently reported, such as the in situ growth of the NCs within the precursor glass by thermal treatment, [20] the incorporation of perovskite thin layers or powder heating the transparent oxide above glass its transition [21] or by femtosecond laser-assisted crystallization induced by a nonlinear localized network glass destruction and giving chance to perovskite crystallization. [22] Many optoelectronic devices feature light-trapping schemes that improve their performance by facilitating the light absorption in the active layer (as in solar cells and photodetectors) or provide pathways to enhance the light emission from light sources. Among the different strategies employed, diffraction Cesium lead halide perovskite nanocrystals have emerged as one of the most promising candidates for manufacturing portable lasers and light sources. In order to harness and exploit their photoluminescence more effectively, the nanocrystals are often accompanied by a photonic scheme that improves light emission. In this work, a quasi-3D photonic crystal is introduced which is composed of a 2D-grating on top of a distributed Bragg reflector (DBR) and provides a greater photoluminescence enhancement than the isolated architectures alone. The quasi-3D photonic crystals suppo...

Monochloracetic acid (CClH2–COOH) is a trimorphic substance. Only one of the three forms is stable, viz.: the α form; whereas the β and γ forms are metastable. The infrared spectrum of the forms α and β has been studied; that of the γ form has not been studied because of its extreme instability. It has been seen that the spectrum of the α form is different from that of the β form. The fundamental frequencies of monochloracetic acid have been assigned, bearing in mind the assignments made by the present authors in another paper for di- and trichloracetic acids. This assignment makes it possible to determine that the displacements which are observed when passing from form α to β chiefly affect the frequencies bound up with the carboxyl group and more especially those in the OH group. This has been confirmed by the preparation of the deuterated derivatives which likewise present themselves in α and β forms, the same relative differences in frequencies being observed. It is inferred from this study that the two crystalline forms differ in the structure of the intermolecular dimers (or polymers). The α form is the conventional dimer with two hydrogen bonds. In the β form this intermolecular bond is probably not the double hydrogen bond, since the OH groups show a greater mobility.

No abstract