Synthesis and Property of Copper-Impregnated α-MnO₂Semiconductor Quantum Dots

Abstract

Because of the superior optical and electrical properties, copper-impregnated size tuneable high-temperature stable manganese dioxide semiconductor quantum dots (SQDs) have been successfully synthesized by a modified chemical synthesis technique. Their size-dependent dielectric properties, semiconducting properties, and current–voltage (I–V) characteristics have been investigated. X-ray diffraction pattern and Raman spectra confirmed that the required phase is present. Because of the different sintering temperature tuneable size of SQDs has been found and confirmed by high-resolution transmission electron microscopy. The band gap energy of the material is found to be 1.25–1.67 eV, measured from Tauc plot using UV–vis absorbance spectrum and their semiconducting properties have been confirmed by the non linear current–voltage (I–V) behavior. Most intense green emission peak of photoluminescence (PL) spectroscopy confirms the oxygen vacancy defect state. The stoke shifting of Raman spectra, UV absorption, and PL emission are the footprint of quantum confinement effect. Incorporation of a little amount of Cu in tetragonal hollandite structure of α-MnO2 generates strain within that structure. This leads to create sufficient crystal defect state as well as rise in dielectric constant accompanied with low dielectric loss and higher ac conductivity. All these highly desirable properties make the SQDs a potential candidate for developing multifunctional photo-electronic devices. Owing to the tuneable band gap and electronic transport of the SQDs, we realized that the controllable size paves the way for designing SQDs possessing unique properties for optical and electronic device applications. Using this material as a high dielectric separator, a high-performance supercapacitor has been successfully fabricated which can light up 15 light-emitting diodes for 47 min 23 s after charging them only for 30 s.

The effects of Fe-doping on MnO2: phase transitions, defect structures and its influence on electrical properties

“…The vibrational lattice features of the RS spectroscopy data provide a reliable description of different local structural as well as crystalline disorders or defects of the MnO 2 related compound. 30 Considering the XRD analysis, α-MnO 2 has a body-centered tetragonal structure with space group I 4/ m , and the RS spectroscopy factor group analysis indicates that MnO 2 will be assigned as 15 spectroscopic modes of 6A g + 6B g + 3E g . However, it might be difficult to observe these Raman-active modes in the polycrystalline samples due to the low polarizabilities of some of these modes and the overlap of incompletely resolved modes.…”

“… 29 The goodness of fit was determined by the reliability parameter R wp and is shown in Table 2 . Meanwhile the dislocation density ( δ ) represents the amount of defects present in the samples, and this is defined as the length of dislocation lines per unit volume of the crystal and was calculated using the equation, 30 where D is the crystallite size.…”

Development of α‐MnO2 Nanowire with Ni‐ and (Ni, Co)‐Cation Doping as an Efficient Bifunctional Oxygen Evolution and Oxygen Reduction Reaction Catalyst

“…The band at low-frequency region of 180 cm À 1 and high-frequency region of 375 cm À 1 as well as 640 cm À 1 corresponds to Ni-doped MnO 2 octahedra within a tetragonal framework. [43,44] Remarkably, the intensity variation and peak shift (640 cm À 1 ) are found in 8Ni and 10NiÀ MnO 2 materials. This suggested that the strengthening of the MnÀ O bond and effective replacement of K + by Ni 2 + cations in the α-MnO 2 tunnel structure.…”

Ionic-Liquid-Assisted Synthesis of Mixed-Phase Manganese Oxide Nanorods for a High-Performance Aqueous Zinc-Ion Battery

“…A more comprehensive and accurate explanation of the structural information on the synthesized material was obtained using FTIR and Raman spectroscopy. The MO crystallizes into a tetragonal body-centered configuration having an I 4/ m space group, which generally shows spectroscopic species of A g (6), B g (6), and E g (3) bands . As shown in Figure d, the Raman spectra show three prominent peaks at the 182, 572, and 633 cm –1 samples and three low-intensity peaks at 274, 382, and 481 cm –1 for MO and ILMO.…”