Browsing by Author "Bahadur Rai, Shyam"

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    An assembly and interaction of upconversion and plasmonic nanoparticles on organometallic nanofibers: Enhanced multicolor upconversion, downshifting emission and the plasmonic effect
    (Institute of Physics Publishing, 2017) Singh, Priyam; Shahi, Praveen Kumar; Prakash, Rajiv; Bahadur Rai, Shyam
    We present novel inorganic-organic hybrid nanoparticles (HNPs) constituting inorganic NPs, NaY0.78Er0.02Yb0.2F4, and organometallic nanofiber, Tb(ASA)3Phen (TAP). X-ray diffraction, Fourier transform infrared absorption and transmission electron microscopy analyses reveal that prepared ultrafine upconversion NPs (UCNPs (5-8 nm)) are dispersed on the surface of the TAP nanofibers. We observe that the addition of TAP in UCNPs effectively limits the surface quenching to boost the upconversion (UC) intensity and enables tuning of UC emission from the green to the red region by controlling the phonon frequency around the Er3+ ion. On the other hand, TAP is an excellent source of green emission under ultraviolet exposure. Therefore prepared HNPs not only give enhanced and tunable UC but also emit a strong green color in the downshifting (DS) process. To further enhance the dual-mode emission of HNPs, silver NPs (AgNPs) are introduced. The emission intensity of UC as well as DS emission is found to be strongly modulated in the presence of AgNPs. It is found that AgNPs enhance red UC emission. The possible mechanism involved in enhanced emission intensity and color output is investigated in detail. The important optical properties of these nano-hybrid materials provide a great opportunity in the fields of biological imaging, drug delivery and energy devices. © 2017 IOP Publishing Ltd.
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    Monochromatic NIR UC emission in Tm3+/Yb3+ co-doped GdVO4 phosphor: The effect of the Bi3+ ion concentration and pump power of a diode laser
    (OSA - The Optical Society, 2018) Dwivedi, Abhishek; Kumar, Devendra; Bahadur Rai, Shyam
    A Tm3∕Yb3∕Bi3 co-doped GdVO4 phosphor sample has been synthesized using a high-temperature solid-state reaction technique. The X-ray diffraction patterns reveal pure phase formation and crystalline behavior of the synthesized samples. Intense blue and NIR upconversion emissions have been observed upon excitation with a 980 nm diode laser. It is found that the addition of the Bi3 ion to the phosphor reduces the intensity of blue emission and enhances the NIR emission intensity to the extent that NIR emission is nearly monochromatic [I NIR∕IBlue ∼ 14]. This ratio is further improved up to 70 times (almost monochromatic) by varying the pump power of the diode laser. Thus, this material can be used as a cheap source of monochromatic NIR emission at 800 nm for bioimaging. © 2018 Optical Society of America