Availability of sufficient light for growth optimization of plants in greenhouse environment during winter is a major challenge, as light during winter is significantly lower than that in the summer. The most commonly used artificial light sources (e.g., metal halide lamps, high pressure sodium lamps, and high fluorescent lamps) are of low quality and inefficient. Therefore, better options should be developed for sustaining agricultural food production during low levels of solar radiation. In recent advances, light-emitting diodes (LEDs) have remarkable potential as supplemental source of light for promoting plant growth. LEDs are novel and versatile source of light with cool emitting surface, wavelength specificity, and low electric power requirement. In the present study, we provided a contemporary synthesis of existing evidence along with our hypothetical concepts to clarify how LED approach could be an efficient and cost-effective source of light for plant growth and development especially in closed production system. In comparative analysis of common artificial vs. LED lighting, we revealed that spectral quality of LEDs can have vivid effects on plant morphogenesis and anatomy. We also discussed the influence of different colors of LEDs on growth performance of plants and provided the cost benefit analysis of using LEDs compared with other traditional sources. Overall, we hope that this article will be of great worth in future due to its practical implications as well as research directions.
Violet light‐emitting diodes (LEDs) with emission at 400 nm are very important for solid‐state lighting, high‐density information storage, display technology, and biology medical treatment. Wide band‐gap semiconductors and/or the semiconductor quantum dots (QDs), typically based on heavy metals such as cadmium and lead, are promising candidates for the violet LEDs, but so far these have had external quantum efficiencies (EQEs) lower than 0.31% (luminance 147.6 cd cm−2; 410 nm). Herein, violet light‐emitting materials and the violet LED devices based on carbon dots (CDots) are presented. The CDots have absolute photoluminescence quantum yield of 23.9% and produce two‐narrow‐peak emission at 382 and 401 nm with narrow full‐width at half‐maximum about 30 nm, respectively. The violet LEDs based on these CDots display high performance with a maximum luminance of 163 cd m−2 (electroluminescence peak located at 408 nm; Commission International de I'Eclairage color coordinate (0.180, 0.121)) and high EQE of 0.831%, exceeding that of previously reported semiconductor QDs‐based violet LEDs. Moreover, these CDots‐based violet LEDs have a high current efficiency of 0.62 cd A−1, a long lifetime (T50, 50 h), as well as a low turn‐on voltage of 3.7 V.
CsPbBr 3 perovskite quantum dots (QDs) have attracted great attention due to their different photoluminescent and electronic properties. However, the toxicity and low stability hinder their practical application. Here, low-toxicity Sn-substituted cesium lead bromide perovskite QDs were synthesized via the room temperature crystallization method. A phase transition of the perovskite quantum dots with the concentration of Sn increasing was found: the crystal phase of CsPbBr 3 :Sn perovskite QDs starts to be transformed into Cs 4 PbBr 6 :Sn perovskite QDs when the SnBr 2 precursor exceeds 30 at. %. In this process, the controlled-color emission of perovskite QDs from green to blue can be realized. To improve the stability of quantum dots, CsPbBr 3 :Sn@SiO 2 and Cs 4 PbBr 6 :Sn@SiO 2 were synthesized via a simple one-step synthesis with hydrolysis of tetramethoxysilane in toluene solution containing perovskite QDs. The results show that CsPbBr 3 :Sn@SiO 2 and Cs 4 PbBr 6 :Sn@SiO 2 exhibited higher water stability and water solubility than pure QDs. In a mixed solution of toluene and water, the PL intensity of the CsPbBr 3 :Sn@SiO 2 retained 46.7% and the Cs 4 PbBr 6 :Sn@SiO 2 was 59.6% even after 24 h of reaction compared with the initial intensities. These quantum dots with good stability and luminescent property developed in this work are expected to be widely used in light-emitting diodes.
There has been a growing interest in electronic and optoelectronic devices based on heterostructures between atomically thin 2D and 3D semiconductor materials. This paper proposes a 2D molybdenum disulfide (MoS2)/3D germanium (Ge) junction field‐effect transistor (JFET). Typical electrical characteristics of the JFET are observed, with a low subthreshold swing of ≈88 mV/dec and a high on/off ratio of ≈105. The device exhibits a bidirection photoresponse in which the photocurrent polarity is reversed depending on the wavelength of light. Under visible illumination at 532 nm, the positive photoresponsivity of this device can be modulated by the gate voltage, reaching a peak value of 66 A W−1. In contrast, the device exhibits a tunable negative photoresponse behavior under an infrared illumination of 1550 nm. This is attributed to the competition between the negative photoresponse from the bolometric effect in MoS2 and the positive photoresponse from photogenerated carriers in Ge. Based on these interesting characteristics in this JFET, three controllable current states (−1, 0, and 1) are realized by changing the gate voltage and infrared light. These results indicate that the device has promising potential as a multifunctional optoelectronic unit, including signal amplification, broadband photodetection, and multilogic calculations.
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