[en] Highlights: • Continuous wave random lasing in a dye doped polymer film has been demonstrated. • A significant reduction in lasing threshold has been demonstrated. • Speckle-free imaging is demonstrated by using the random laser illumination. The applications of random laser (RL) are still restricted, due to its complexity, high lasing threshold, unstable nature, difficulty in tuning and modulating its light emission characteristics. However, here a low threshold, continuous wave (CW) RL system has been designed in a fluoresecent laser dye (namely DCM) -doped in a polymer film with ZnO micro-cabbages as scatterers. Interestingly, by putting the active medium inside an external feedback (ExFB) system, a narrowed and stable RL emission at ~598 nm is observed with the subsequent reduction of CW lasing threshold (^CWI_Th) by ~2.4 times. The effective cavity length (L_eff) has been varied by an ingenious approach to demonstrate the role of L_eff over the RL emission characteristics and the experimental results are supported by a theoretical explanation. The statistical fluctuation in the position of generated modes over time and the role of pump volume amplification on the emission characteristics of the developed RL has been studied in detailed. Thus, it is found here that due to the presence of ExFB, reinjection of pump light into scattering-formed cavities has taken place which has led to the generation of stable RL modes with the reduction of ^CWI_Th. The temporal coherency of the ExFB based RL light is found to be ~3.2 times less than that of a conventional He–Ne laser light. As a result, we could demonstrate here speckle free imaging with much lowered value of speckle contrast (C) on two different model systems, such as commercially available carbon film-coated TEM grid and cell membrane of Allium cepa. It is expected that this report will open up new possibilities for the development of stable and tunable RLs with other laser dyes for various optoelectronic applications including in bio-imaging.

[en] Highlights: • 3D printed polymer scaffold with different geometry and surface porosity. • In situ growth of ZnO nanoflakes on 3D printed scaffolds. • The synergistic effect between the photodegradation and adsorption in a one system. • Smartphone-based user-friendly facile detection of dye removal efficiency. • RGB calculation for quantitative analysis using colorimetric absorption technique. Industrialization harms the quality of water; therefore, cleaning and monitoring water sources are essential for sustainable human health and aquatic life. An increase in active surface area and porosity can result in quick and efficient cleaning activity. 3D printing can build porous architecture with controlled porosity and active surface area. Here, catalytically active ZnO nanosheets were grown on the surface of 3D printed architecture (Schwarzites and Weissmuller) with different porosity and surface area. The Weissmuller structure along with ZnO, has shown better catalytic performance due to its higher porosity (~69%) and high active surface area, compared to Schwarzites structure. Synergistic effect of adsorption and photodegradation has resulted in ~95% removal efficiency of mixed dye within 10 min by Weissmuller structure. The dye degradation efficiency was determined using colorimetric measurements with a regular smartphone for real-time quantitative investigation of dye removal efficiency. Most importantly, decorated 3D printed structures exhibit high structural stability without residuals (ZnO nanosheets) in water after performing the recycling experiment. Therefore, the decorated 3D printing structures and colorimetric detection method will offer a user-friendly versatile technique for analysis of removal efficiency of toxic components in different polluted water sources without using high-end sophisticated instruments and complicated procedures.

[en] Highlights: • A two-step synthesis approach is proposed to synthesize 2D rGO-ZnO (rGZn) nanocomposites. • Cotton smart fabrics have been prepared with the synthesized rGZn nanocomposites. • Synthesized nanocomposites show high photocatalytic and self-cleaning properties. • The amount of ZnO is varied in nanocomposites to achieved high photo-catalytic efficiency. • Methylene blue dye degradation of ∼91% is achieved only within 60 min. - Abstract: Recently, research activities are focused on development of 2D reduced graphene oxide (rGO) based semiconductor nanocomposite materials for boosting up its catalytic applications. In this work, a rarely reported green synthesis approach has been envisioned to synthesize in-situ 2D rGO-ZnO (rGZn) nanocomposites from Apple juice and zinc acetate. Also the composition of the samples has been optimized to achieve high photocatalytic and self-cleaning properties by the formation of reactive oxidation species. The samples are characterized for their microstructural, optical absorption and photoluminescence properties. It has been tested that rGZn nanocomposites are capable of removing a test dye, namely methylene blue (MB) from water and achieved the highest dye degradation efficiency of ∼91% within only 60 min under UV–vis light irradiation. A smart cotton fabric (CF) coated with rGZn has been prepared and demonstrated its photocatalytic self-cleaning property by degradation of MB, rhodamine B dyes and tea stains on it even under sunlight irradiation, which is scarcely available in the literature. Therefore, this work may open a new avenue of research for low cost and easy synthesis of rGO-semiconductor nanocomposites with high photocatalytic properties for industrial applications as well as for development of rGO based smart fabric for real-life applications.

[en] Highlights: • New type of triboelectric driven flexible STPC has been fabricated on a normal sheet of paper. • The STPC exhibits P_max, V_oc, & I_sc of ~0.67 μW, ~3.82 V, & ~0.20 μA, respectively in 1 kPa impact. • V_oc of STPC shows linear responses to number of folding, externally applied weight, & temperature. • dV_oc/dT of the STPC is found to be 0.093VK^-1 in the temperature range of 293–323 K. • V_oc of STPC is increased linearly with externally weight up to 72 kg. -- Abstract: The recent progresses on smart technology and on Internet of Thing (IoT) have created a huge demand on development of cost-effective and environment friendly alternate energy sources, by using light weight, low cost, flexible and easily available materials. However, in this work, a new type of triboelectric driven flexible and self-charging triboelectric power cell (STPC) has been fabricated by using commercially available materials, namely bulk MoS₂, non-conductive glue, graphite powder, and normal sheet of paper. Interestingly, STPC exhibits excellent output performances with the maximum power, open circuit voltage (V_oc), and short circuit current of ~0.67 μW, ~3.82V, and ~0.20μA, respectively under a periodic pressure of amplitude of 1 kPa. The V_oc of the fabricated device is found to be highly sensitive and showed linear response to number of folding (N), externally applied weight (W), and temperature (T). For instance, dV_oc/dT and dV_oc/dW of STPC is found to be 0.093VK^-1 and 0.2Vkg^-1 in temperature and weight range of 293–323K and 50–72kg, respectively. Further, we have calculated the figure of merit of the developed device by calculating the values of relative sensitivity coefficients (S) of V_oc w.r.t. N, W, and T and the highest obtained values of S are ~1.12, ~4.35, and ~16.00, respectively. The reported simple method of development of paper based STPC cell, based on only commercially available materials, can be utilized further for development of flexible, light weight, low cost and eco-friendly wearable sensing devices.

[en] Magnetism in semiconductor two-dimensional (2D) materials is gaining popularity due to its potential applications in memory devices, sensors, spintronics, and biomedical applications. Here, 2D cobalt telluride (CoTe) has been synthesized from its bulk crystals using a simple and scalable liquid-phase exfoliation method. The ultrathin CoTe shows ~ 400 times enhancement in its magnetic saturation values compared to the bulk form. The UV-Vis absorption spectra reveal superior absorption in the high-energy region, suggesting a semiconducting nature. Furthermore, we explain the bandgap and origin of high magnetic behavior by density functional theory (DFT) calculations. The 2D CoTe shows a larger magnetism compared to bulk CoTe due to the reduced coordination number of the surface atoms, shape anisotropy, and surface charge effect. Additionally, the semiconducting nature and surface charges are fruitfully utilized for degradation of different toxic dyes under magnetic field and visible light irradiation. Therefore, atomically thin magnetic CoTe can give a new perspective to the separation of charge carriers.