Browsing by Author "Singh, Priyam"
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PublicationArticle A strategy to achieve efficient dual-mode luminescence in lanthanide-based magnetic hybrid nanostructure and its demonstration for the detection of latent fingerprints(Academic Press Inc., 2017) Shahi, Praveen K.; Singh, Priyam; Singh, Akhilesh K.; Singh, Sunil K.; Rai, Shyam B.; Prakash, RajivWe have synthesized a novel inorganic-organic hybrid nanostructure (IOHN) composed of fluoride nanophosphor (NaGd0.78Er0.02Yb0.2F4) and β-diketones complex (Eu(DBM)3Phen). The Le Bail fitting of X-ray diffraction data suggests that the nanophoshor crystallizes in a hexagonal structure (P63/m space group). The TEM studies reveal that the nanophosphor and the IOHN both have average particle size of 6–8 nm. The Eu(DBM)3Phen and NaGd0.78Er0.02Yb0.2F4 show characteristic down-shifting (DS) and up-conversion (UC) emission, under UV and NIR excitation, respectively. The IOHN comprises an excellent dual-mode optical features (DS and UC) of both the phases. Energy transfer from Er3+ (doped in inorganic phase) to Eu3+ (coordinated in organic phase) clearly demonstrates for a viable coupling between both the phases. IOHN material was found to be unique for the visualization of latent fingermarks. Because of ultrafine particle size the surface to volume ratio is relatively higher which improves the attachment of particles with the fingermarks. On the other hand, the strong paramagnetic property helps to remove excess material with magnetic wand easily. These properties provide an opportunity to probe even very weak fingermarks. Notwithstanding this, the dual-mode emission is useful for the visualization of latent fingermarks on multi-color surfaces as well. © 2016 Elsevier Inc.PublicationArticle 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, ShyamWe 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.PublicationArticle Colour tunability in a bimodal fluorescent hybrid nanostructure UCNPs@AuNPs@QDs(Elsevier B.V., 2020) Singh, Priyam; Singh, P.; Prakash, R.; Rai, S.B.; Singh, S.K.In the present work, lysine modified NaY0.78Er0.02Yb0.2F4 upconversion nanoparticles (UCNPs, positively charged) and lysine modified ZnSe:Mn2+ quantum dots (QDs, positively charged) are attached onto the surface of citrate reduced gold nanoparticles (AuNPs, negatively charged). The gold nanoparticles not only entangle the QDs and the UCNPs, through electrostatic interaction, but also tune the optical properties of UCNPs through the effect of surface plasmon resonance. The hybrid nanostructure gives green emission both through photoluminescence (under UV excitation) and through photon upconversion (under IR light excitation) process. The colour tuning is observed through variation in the size of QDs and through plasmonic effect of gold nanoparticles. In both the cases, the colour of emission gradually changes from green to red. The colour tunability and bi-modal photon conversion property of this material could be useful for its application in the field of bio-imaging and solar energy harvesting. © 2020 Korean Physical SocietyPublicationArticle Effect of Li+ ion sensitization and optical temperature sensing in Gd2O3: Ho3+/Yb3+(Elsevier B.V., 2016) Singh, Priyam; Shahi, P.K.; Rai, Anita; Bahadur, A.; Rai, S.B.Ho3+/Yb3+ codoped Gd2O3 phosphor has been synthesized by solution combustion method. The concentrations of Ho3+ and Yb3+ were optimized to be 0.3 and 2.0 mol% respectively for maximum emission intensity. The effect of Li+ ion co-doping on phase structure and photo luminescence were investigated. It is found that there is no change in phase of the sample due to Li+ ion co-doping. However the Upconversion (UC) and Downshifting (DS) emission show a remarkable enhancement in intensity. It is concluded that, this enhancement in the emission intensity is mainly due to the change in crystal field around the Ho3+ ion and reduction in quenching centers. The optimum doping concentration of Li+ ion was found to be 20 mol%. We have further explored the temperature sensing behavior using the FIR technique. The maximum sensitivity is found to be 0.0092 K−1 at 505 K. © 2016 Elsevier B.V.PublicationArticle Generation of red-NIR bi-modal fluorescence in hybrid nanostructure(Elsevier Ltd, 2020) Singh, Priyam; Singh, S.K.; Singh, Prabhakar; Prakash, R.; Rai, S.B.We have developed an ultrafine (<15 nm) hybrid nanoparticle (HNPs) consisting of lanthanide doped upconversion nanoparticles (UCNPs, NaY0.797Tm0.003Yb0.2F4), manganese doped zinc selenide quantum dots-(QDs, Mn:ZnSe) and silver nanoparticles (AgNPs). Synthesized HNPs involves electrostatic interaction among constituent particles. Thus, the coupling among constituent particles is relatively more strong contrary to the usual weak Van der Waals force based HNPs. HNPs emit nearly pure red-NIR emission both through normal fluorescence (under UV light excitation) and through photon upconversion process (under NIR excitation). AgNPs act as an optical filter for blue emission both for- (i) band to band transition of ZnSe and (ii) UC emission of Tm3+ ions (1G4→3H6) and thus turns the overall emission color to be in red-NIR region. Decay time measurement probes that, quenching of blue emission bands are primarily due to resonance energy transfer from UCNPs and QDs to the AgNPs (40 μL) with an energy transfer efficiency of 36% and 70%, respectively. These ultrafine and bimodal emitting HNPs could be suitable as optical imaging probe, in first biological window, and for other optoelectronic applications. © 2019 Elsevier LtdPublicationArticle Host-Sensitized NIR Quantum Cutting Emission in Nd3+ Doped GdNbO4 Phosphors and Effect of Bi3+ Ion Codoping(American Chemical Society, 2016) Shahi, Praveen Kumar; Singh, Priyam; Rai, Shyam Bahadur; Bahadur, AmreshHost-sensitized near-infrared quantum cutting (QC) emission has been demonstrated in Nd3+ doped Gd1-xNdxNbO4 phosphors for various x values. Further, the effect of Bi3+ ion addition as a sensitizer on near-infrared QC is studied in detail. X-ray diffraction confirms a monoclinic structure for pure and Nd3+ doped phosphors. Pulsed laser excitation at 266 nm of Gd1-xNdxNbO4 and Gd(0.99-x)NdxBi0.01NbO4 causes efficient room-temperature energy transfer from the NbO43- to the Nd3+ ions and the NbO43- and Bi3+ ions to the Nd3+ ions, respectively, which emits more than one near-infrared photon for single impinging ultraviolet photon. The emission band of Nd3+ shows unusual character where the intensity of the 4F3/2-4I9/2 transition at 888 nm is higher than the intensity of the transition 4F3/2-4I11/2 at 1064 nm, due to energy transfer from GdNbO4 host to Nd3+ ion. Using photoluminescence lifetime studies, the quantum cutting efficiencies are found to be the maximum 166% and 172% for Gd(0.95)Nd0.05NbO4 and Gd(0.94)Nd0.05Bi0.01NbO4, respectively. The present study could establish Nd3+ ion as an alternative of Yb3+ ion for near-infrared quantum cutting. This work facilitates the probing of Nd3+ ions doped phosphor materials for next generation Si-solar cells. © 2016 American Chemical Society.PublicationArticle Lanthanide doped ultrafine hybrid nanostructures: Multicolour luminescence, upconversion based energy transfer and luminescent solar collector applications(Royal Society of Chemistry, 2017) Singh, Priyam; Shahi, Praveen Kumar; Singh, Sunil Kumar; Singh, Akhilesh Kumar; Singh, Manish Kumar; Prakash, Rajiv; Rai, Shyam BahadurWe herein demonstrate novel inorganic-organic hybrid nanoparticles (HNPs) composed of inorganic NPs, NaY0.78Er0.02Yb0.2F4, and an organic β-diketonate complex, Eu(TTA)3Phen, for energy harvesting applications. Both the systems maintain their core integrity and remain entangled through weak interacting forces. HNPs incorporate the characteristic optical behaviour of both the systems i.e. they give an intense red emission under UV excitation, due to Eu3+ in organic complexes, and efficient green upconversion emission of Er3+ in inorganic NPs for NIR (980 nm) excitation. However, (i) an energy transfer from Er3+ (inorganic NPs) to Eu3+ (organic complex) under NIR excitation, and (ii) an increase in the decay time of 5D0 → 7F2 transition of Eu3+ for HNPs as compared to the Eu(TTA)3Phen complex, under different excitation wavelengths, are added optical characteristics which point to an important role of the interface between both the systems. Herein, the ultra-small size (6-9 nm) and spherical shape of the inorganic NPs offer a large surface area, which improves the weak interaction force between both the systems. Furthermore, the HNPs dispersed in the PMMA polymer have been successfully utilized for luminescent solar collector (LSC) applications. © The Royal Society of Chemistry 2017.PublicationArticle Photo-physical studies of ultrasmall upconversion nanoparticles embedded organometallic complexes: Probing a dual mode optical sensor for hydrogen peroxide(Elsevier B.V., 2019) Singh, Priyam; Singh, Prabhakar; Prakash, Rajiv; Rai, Shyam BahadurHere, we report an upconversion nanoparticles (UCNPs) embedded organomettalic complex for detection of hydrogen peroxide (H2O2). The structural as well as the optical properties of the hybrid nanoparticles (HNPs) have been studies to confirm the interaction as well as energy transfer mechanism. The structural characterization confirm the weak interacting force between the UCNPs and the organic complex in HNPs. The optical studies reveal that, HNPs show characteristic optical behaviour of both the phases i.e. it gives an intense downconverted red emission under UV excitation, due to the presence of organic part (Eu3+ ion) as well as an efficient blue upconverted emission from inorganic part (Tm3+ ion) under NIR excitation. The energy transfer between the inorganic (Tm3+ ion) and the organic (Eu3+ ion) material has been observed, which confirms the effective attachment of both the phases in HNPs. The upconversion and downconversion emission properties, have been have successfully utilized for dual mode H2O2 detection. © 2019PublicationArticle Sunlight activated lanthanide complex for luminescent solar collector applications: Effect of waveguide matrix(Institute of Physics Publishing, 2017) Shahi, Praveen Kumar; Singh, Priyam; Rai, Shyam BahadurThe performance of Eu(DBM)3Phen complex (EDP) dispersed in PMMA poly-(methyl methacrylate) polymer matrix, as simple planner luminescent solar collectors (LSCs) is demonstrated using spectroscopic and photovoltaic (PV) measurements. The organic ligands absorb ultra-violet-blue (UV-blue) radiation (220-450 nm) very efficiently and transfer its energy to the Eu3+ ion, which gives an intense red emission even in sunlight exposure. The excellent optical properties of EDP in PMMA permit its coating on the front surface of c-Si solar cell (10 × 10 cm2) for PV measurements. The PV characterizations reveal the improvement in the short circuit current density (J sc) of PV cell and maximum improvement is found to be 4.6% for 2.5 wt% EDP concentration in PMMA matrix. The efficiency of solar cell increases from 17.22% to 18.33% for bare and 2.5% EDP in PMMA. At a higher concentration of EDP, the thin film starts losing its transparency and hence PV efficiency decreases. These results illustrate that a EDP complex combined with a PV cell could work as a prototype of a new generation solar cell. © 2017 IOP Publishing Ltd.PublicationArticle Upconversion and downshifting emissions of Ho3+-Yb3+ co-doped ATiO3 perovskite phosphors with temperature sensing properties in Ho3+-Yb3+ co-doped BaTiO3 phosphor(Elsevier Ltd, 2021) Singh, Priti; Yadav, Ram Sagar; Singh, Priyam; Rai, Shyam BahadurIn this work, we report a comparative study on upconversion and downshifting properties of Ho3+-Yb3+ co-doped ATiO3 (A = Ca, Ba & Sr) perovskite phosphors for the first time. The phosphor samples are prepared via solid state reaction method in a programmable furnace at 1523 K. The phosphor samples are structurally characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The EDS analyses show the presence of the desired elements used in the synthesis. The vibrational structures of the phosphor samples are studied by Fourier transform infrared (FTIR) technique. The diffuse reflectance spectra show a number of bands in the UV–vis–NIR regions due to Ho3+ and Yb3+ ions. The optical band gap (Eg) is calculated using Wood and Tauc relation and its values are found to be 3.61, 3.20 and 3.32 eV for the Ho3+-Yb3+ co-doped ATiO3 (A = Ca, Ba & Sr) perovskite phosphor samples, respectively. The upconversion emission spectra are monitored by exciting these phosphor samples at 980 nm. The phosphor samples give intense green emission in all the cases. However, the UC emission intensity is higher for the Ho3+-Yb3+ co-doped CaTiO3 perovskite phosphor. These phosphor samples also give intense green downshifting emission upon 419 and 452 nm excitations. The Ho3+-Yb3+ co-doped BaTiO3 perovskite produces relatively larger emission intensity among these phosphors. The lifetime of green emitting level (5F4) of Ho3+ ion shows temporal behavior of these perovskite phosphors. Furthermore, the temperature versus UC emission intensities of the green thermally coupled levels of Ho3+-Yb3+ co-doped BaTiO3 phosphor gives the fluorescence intensity ratio (FIR) and FIR-based relative (SR) and absolute (SA) temperature sensor sensitivities are obtained as 0.0034 K-1 and 0.0050 K-1, respectively at 305 K. Thus, the Ho3+-Yb3+ co-doped ATiO3 (A = Ca, Ba & Sr) perovskite phosphors may be found suitable in display devices, solid state lighting, upconversion based devices and temperature sensing devices. © 2020 Elsevier B.V.
