Biplab Kumar Paul

Nickel oxide (NiO), a wide-band-gap semiconductor with high stability, is promising for optoelectronic and dielectric devices, yet its practical performance is often limited by moderate dielectric response and restricted light-matter interaction. Rare-earth doping offers a pathway to overcome these constraints by simultaneously tuning the structural, optical, and electrical properties. In this work, 1% erbium (Er)- and 1% gadolinium (Gd)-doped NiO nanoparticles were synthesized via a modified chemical route and comprehensively characterized. X-ray diffraction (XRD) confirmed the cubic nature of Er- and Gd-doped NiO, where Er incorporation reduced the crystallite and increased the surface area, facilitating interfacial polarization and an enhanced dielectric response. In contrast, Gd incorporation predominantly altered the electronic structure, narrowing the band gap and strengthening optical absorption. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) imaging confirmed uniform nanostructures, while Raman and X-ray photoelectron spectroscopy (XPS) analyses with Coats-Redfern kinetics indicated improved stability of doped samples. Optical investigations (UV-vis, PL) correlated band gap modulation with dielectric functions, validated through derived parameters such as the refractive index, optical dielectric constant, SELF, and VELF. Temperature-dependent dielectric studies demonstrated strong frequency dispersion linked to charge carrier dynamics originating from dopant-modified band structures. Thus, Er doping primarily boosts dielectric functionality through nanoscale polarization, while Gd doping optimizes optical transitions, together highlighting dopant-controlled correlations in NiO for multifunctional optoelectronic and energy-storage applications.

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 (RS) confirmed that the required phase is present. Due to the different sintering temperature tuneable size of SQDs has been found and confirmed by high resolution transmission electron microscopy (HRTEM). 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) behaviour. Most intense green emission peak of photoluminescence (PL) spectroscopy confirms the oxygen vacancy defect state. The stoke shifting of RS, 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 bandgap 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 able to light up 15 number of LEDs for 47 min 23 sec after charging it only for 30 seconds.