• POORNIMA MITTAL

      Articles written in Bulletin of Materials Science

    • Effect of metal doping on visible light absorption and optical properties of lithium niobate (LiNbO$_3$) crystal: a first-principles calculation

      ASHISH RATURI POORNIMA MITTAL SUDHANSHU CHOUDHARY

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      Electronic and optical properties of pristine and metal-doped lithium niobate crystals are investigated by using first-principles DFT calculations. The results on optical properties suggest that there is a shift in the absorption edge towards visible region (red-shift) for metal-doped structures, in comparison with the pristine lithium niobite. A series of metals are used for doping and it is found that the absorption edge is shifted significantly to the visible region for the dopants; gold (Au), silver (Ag), aluminium (Al) and copper (Cu) due to surface plasma resonance. However, for other metal dopants like iron (Fe), manganese (Mn), molybdenum (Mo) and nickel (Ni), the absorption is slightly improved in the visible region and red-shift is observed. The bandgap of all the doped structures is found to be reduced, this might be proven advantageous for photovoltaic applications, which requires high optical absorption in the visible region. The dielectric constant and refractive index of the pristine and doped structures are also calculated and it is observed that the absorption trend is in accordance with dielectric constant. The optical absorption is enhanced in the visible region due to doping of selected metals (M = Au, Ag, Al, Cu, Fe, Mn, Mo and Ni) making M-lithium niobite a promising material for optoelectronic- and photonic-based applications.

    • Recent advancements over a decade for organic light-emitting diodes: from structural diversity, role of layers, colour emission, material classification, performance improvement, fabrication to applications

      SUGANDHA YADAV POORNIMA MITTAL SHUBHAM NEGI

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      Organic light-emitting diode (OLED) is an emerging technology of organic electronics that exhibits an assortment of salient and attractive features like self-emitting ability, great flexibility, true dark tone, transparency and many more. Along with display applications, OLEDs are prudent for light detection-based applications. Enormous research work has been reported to refine the OLED technology in terms of structures, materials, performance parameters, lifetime and applications. There is a vast scope for developing white OLED devices for utilization in solid-state lighting applications. This review paper summarizes recent advancements in different aspects for OLEDs over the last decade. The main focus is to diversify different multilayer structures of OLEDs highlighting the role and significance of charge injection, charge transport, emission and blocking layers. Also, a timeline analysis for characteristics parameters, layerwise materials and fabrication techniques is presented. Further, different performance improvement techniques based on layers, parameters and colour emission are demonstrated. This article also illustrates prudent applications based on organic thin-film transistor-driven OLED, sensors, military and healthcare. Some challenges and reliability issues are also discussed with a scope for future work for OLED.

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      Posted on July 25, 2019

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