Browsing by Author "Bishnoi, P"

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    A correlation between fractal growth, water contact angle, and SERS intensity of R6G on ion beam nanostructured ultra-thin gold (Au) films
    (2023-03) Jasrotia, P; Priya, B; Kumar, R; Bishnoi, P; Vij, A; Kumar, T
    Introduction: This study focuses on the detection of rhodamine-6G using surface-enhanced Raman scattering (SERS) on gold nanostructures (AuNS) of different sizes. Ion beam irradiation has been carried out to tune the size of AuNS and investigate the underlying mechanisms of sputtering and diffusion that govern their growth. Additionally, the study established a correlation between fractal growth parameters, water contact angle, and SERS detection of R6G. The results of this study offer new insights into the mechanisms of SERS detection on roughened metallic surfaces. Methods: Thermal evaporation was used to deposit an Au thin film on a glass substrate. Subsequent 10 keV Ar+ irradiation was done on Au thin film for fluences ranging from 3×1014 to 3×1016 ions/cm2 to tune the size of AuNS. Rutherford backscattering spectroscopy (RBS) was used to confirm that the decrease in Au concentration under ion beam sputtering was responsible for the tuning in size and structure of AuNS. Fractal dimension (Df) and interface width (w) were used as statistical parameters to control the wettable characteristics of the AuNS surfaces. Results and discussion: The researchers found that the growth of AuNS was governed by ion beam induced sputtering and diffusion mechanisms. They established a correlation between fractal growth parameters, water contact angle, and SERS detection of R6G. They found that a higher surface coverage area of Au NPs with lower fractal dimensions and water contact angles favoured the SERS detection of R6G. This study provides new insights into the mechanisms of SERS detection on roughened metallic surfaces. It is found that the growth of AuNS was governed by ion beam-induced sputtering and diffusion mechanisms, and established a correlation between fractal growth parameters, water contact angle, and SERS detection of R6G. The findings of this study may have applications in the development of more sensitive and efficient SERS-based chemical sensors.
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    Up-converted white light emission in Er3+ doped MgAl2O4 nanocrystals
    (2024-03) Savita; Upadhyay, M; Bishnoi, P; Kumar, S
    This work presents the influence of host defect centers on the photoluminescence characteristics of Mg1 xErxAl2O4 (x = 0.005, 0.01, and 0.03) nanocrystals under UV and near-infrared (NIR) excitations. The spinel-structured nanocrystals are synthesized through the combus tion method. The Rietveld refinement and nuclear magnetic resonance analyses estimated the Er3þ ion occupancy at octahedral and other random sites of the MgAl2O4 lattice, and the existence of various lattice defects. Diffuse reflectance spectra showed broad bands attributed to oxygen vacancies as well as antisite defects and sharp peaks attributed to f–f transitions of Er3þ ions. The upconversion luminescence spectra consisted of sharp emission lines, ascribed to Er3þ ions, in the green and red wavelength regions, which overlapped over the broad curve attributed to intrinsic defects. Further, the UV excited downconversion luminescence spectra showed two broad emission bands in blue–violet and red-NIR regions with a very weak Er3þ ion emission feature. This up- and downconversion emission revealed energy trans fer between host and Er3þ ions via intrinsic defects. As a result, the emission color changes from bluish purple to white by varying the exci tation wavelength from UV to NIR. This rare earth activated luminescence from MgAl2O4 nanocrystals would exhibit potential applications in display devices and solid-state lighting.