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Decentralized water generation and distribution systems have become quite a necessity for places that lack the infrastructure or economic resources of developed water supply systems. Unconventional methods of water production technologies are being proven to be highly beneficial for freshwater production in remote regions devoid of ground or underground water sources. On many occasions, such methods are dependent on the terrain of application. A comparative discussion has been made in this paper on leading technologies in unconventional water production, which has multiple advantages. Methods like absorbing water using desiccant materials, refrigeration systems and atmospheric fog collection systems are some sustainable options that are also eco-friendly and cheap systems. These can be used in various weather conditions like windy sites, desert as well as coastal regions.

Thermoacoustic Refrigeration is a phenomenon in which cooling takes place by using high-intensity sound waves, which is gathering attention of many researchers in recent days. This alternative environment friendly technology could play an important role in near future. The paper is mainly an experimental case study on a thermoacoustic refrigeration system build in a laboratory environment with the commonly available materials. The setup was tested for various frequencies of sound to observe its effect on the drop of temperature. The refrigeration effect was also studied for various stack materials. It was observed that sinusoidal waves are better responsive to the production of the refrigeration effect. Moreover, the effect is more pronounced for paper-foil made stack.

Bulk gallium phosphide (GaP) crystallizes in the zinc-blende (ZB) structure and has an indirect bandgap. However, GaP nanowires (NWs) can be synthesized in the wurtzite (WZ) phase as well. The contradictory theoretical predictions and experimental reports on the band structure of WZ GaP suggest a direct or a pseudo-direct bandgap. There are only a few reports of the growth and luminescence from WZ and ZB GaP NWs. We first present a comprehensive study of the gold-catalyzed growth of GaP NWs via metalorganic vapor phase epitaxy on various crystalline and amorphous substrates. We optimized the growth parameters like temperature, pressure and reactant flow rates to grow WZ GaP NWs with minimal taper. These wires were characterized using electron microscopy, x-ray diffraction, Raman scattering and photoluminescence spectroscopy. The luminescence studies of bare GaP NWs and GaP/AlGaP core-shell heterostructures with WZ- and ZB-phase GaP cores suggest that the WZ-phase GaP has a pseudo-direct bandgap with weak near-band-edge luminescence intensity.

The peak of the photoluminescence (PL) spectrum associated with the A − trion in monolayer MoS2 on SiO2/Si substrate is typically red shifted in energy relative to its absorption peak by ~20 meV. Circular polarization anisotropy and pump laser intensity dependence of PL indicates that the A − trion is not localized at a defect. Raman lines in monolayer MoS2 are enhanced and additional lines are seen when the excitation laser has photon energy close to the trion/exciton absorption resonance, indicating their coupling with phonons. Analysis of time resolved PL measurements show that the A − trion emission has a finite rise time of ~25 ps, unlike the defect bound exciton emission which is also seen. The above characteristics when considered together suggest that trions in monolayer MoS2 could be subject to momentary weak self-trapping through interaction with phonons, a hitherto unexplored property of trions/excitons in two-dimensional transition metal dichalcogenide semiconductors.

This paper reports polarization and temperature dependent contactless electroreflectance (CER) and photoluminescence (PL) study of strain compensated short period superlattices on GaAs(001) substrates which show self-organized lateral composition modulation (LCM) in the form of alternate In/Ga rich regions along the [110] direction in the (001) plane. The LCM related PL peak position is at a lower energy as compared to the corresponding feature in the CER spectrum and the difference is found to be the same as the activation energy for thermal quenching of the PL signal. These results have been explained by suggesting that the PL signal arises mainly from recombination of carriers localized at potential fluctuations (In rich regions with excessively high In concentration) within the lateral superlattice (LS) structure that is formed due to the LCM while the CER feature arises from transitions between the minibands of the average LS structure. The PL signal is quenched due to thermal excitation of the carriers from these excessively In rich regions into the minibands. The LS band gap energy is accurately determined and its implication for the random alloy model used to describe the electronic band structure of such systems is discussed. The temperature dependences of critical point energies have also been measured and analysed.

We have studied the interdiffusion process on the group V sublattice in thermally annealed, undoped strained single quantum wells by comparing the results of contactless electro-reflectance spectroscopy with theoretically estimated optical transition energies. We show that the interdiffusion process in this system is Fickian. We estimate the activation energy for the interdiffusion process to be , which is low compared to those reported for other III-V-alloy-based heterostructures.

Temperature dependence of the photoluminescence (PL) peak energy of bulk and quantum well (QW) structures is studied by using a new phenomenological model for including the effect of localized states. In general an anomalous S-shaped temperature dependence of the PL peak energy is observed for many materials which is usually associated with the localization of excitons in band-tail states that are formed due to potential fluctuations. Under such conditions, the conventional models of Varshni, Vi?a and Passler fail to replicate the S-shaped temperature dependence of the PL peak energy and provide inconsistent and unrealistic values of the fitting parameters. The proposed formalism persuasively reproduces the S-shaped temperature dependence of the PL peak energy and provides an accurate determination of the exciton localization energy in bulk and QW structures along with the appropriate values of material parameters. An example of a strained InAs0.38P0.62/InP QW is presented by performing detailed temperature and excitation intensity dependent PL measurements and subsequent in-depth analysis using the proposed model. Versatility of the new formalism is tested on a few other semiconductor materials, e.g. GaN, nanotextured GaN, AlGaN and InGaN, which are known to have a significant contribution from the localized states. A quantitative evaluation of the fractional contribution of the localized states is essential for understanding the temperature dependence of the PL peak energy of bulk and QW well structures having a large contribution of the band-tail states.

Taking M-plane oriented GaN quantum wells (QW) as an example, it is shown that the finite out-of-plane crystal momentum arising from quantum confinement modifies valence band mixing in a way that can significantly alter the emission polarization properties of strained non-polar oriented wurtzite group III-nitride QWs. For certain values of strain, the emission polarization direction can rotate by 90° either within the QW plane, or from being out-of-plane to being in-plane which is desirable for light emission applications. The study based on a k · p type perturbation theory simultaneously accounts for the influence of anisotropic in-plane strain which arises in such QWs and also affects the optical polarization properties. An important practical implication of these results is that M-plane oriented AlxGa1−xN QWs under anisotropic in-plane tensile strain can work as efficient ultra-violet light emitters, unlike bulk AlxGa1−xN films with identical composition and strain. After including the influence of the out-of-plane crystal momentum, the emission polarization criterion allows for larger concentration of Al in such QW active layers if the well width is kept sufficiently small. These results are also applicable to A-plane oriented QWs.

The authors present a comparative study of photoluminescence excitation (PLE) and absorption spectra of CdSe–ZnS core–shell quantum dot ensembles, with mean core diameters ranging from 2.6 to 7.2 nm. The larger dots show a threshold phenomenon wherein for excitation photon energy greater than a value E th, the PLE and absorption spectra diverge abruptly. Beyond E th the PLE signal tends to decrease while absorption continues to increase. Results are compared with electronic structure calculations based on a spherical core–shell potential model. One finds that E th matches with the minimum photon energy required to create holes with energy equal to the core–shell potential energy barrier for holes. These holes, more exposed to shell surface defects, are likely to be lost through non-radiative pathways thereby reducing luminescence. Part of the increase in absorption at higher energies can be attributed to normally forbidden transitions, whose oscillator strength is shown to increase with increase in the transition energy.