Praveen Kumar Shahi

Host-Sensitized NIR Quantum Cutting Emission in Nd3+ Doped GdNbO4 Phosphors and Effect of Bi3+ Ion Codoping

Host-sensitized near-infrared quantum cutting (QC) emission has been demonstrated in Nd(3+) doped Gd(1-x)Nd(x)NbO4 phosphors for various x values. Further, the effect of Bi(3+) ion addition as a sensitizer on near-infrared QC is studied in detail. X-ray diffraction confirms a monoclinic structure for pure and Nd(3+) doped phosphors. Pulsed laser excitation at 266 nm of Gd(1-x)Nd(x)NbO4 and Gd(0.99-x)Nd(x)Bi(0.01)NbO4 causes efficient room-temperature energy transfer from the NbO4(3-) to the Nd(3+) ions and the NbO4(3-) and Bi(3+) ions to the Nd(3+) ions, respectively, which emits more than one near-infrared photon for single impinging ultraviolet photon. The emission band of Nd(3+) shows unusual character where the intensity of the (4)F(3/2)-(4)I(9/2) transition at 888 nm is higher than the intensity of the transition (4)F(3/2)-(4)I(11/2) at 1064 nm, due to energy transfer from GdNbO4 host to Nd(3+) ion. Using photoluminescence lifetime studies, the quantum cutting efficiencies are found to be the maximum 166% and 172% for Gd(0.95)Nd(0.05)NbO4 and Gd(0.94)Nd(0.05)Bi(0.01)NbO4, respectively. The present study could establish Nd(3+) ion as an alternative of Yb(3+) ion for near-infrared quantum cutting. This work facilitates the probing of Nd(3+) ions doped phosphor materials for next generation Si-solar cells.

Revelation of the Technological Versatility of the Eu(TTA)3Phen Complex by Demonstrating Energy Harvesting, Ultraviolet Light Detection, Temperature Sensing, and Laser Applications

We synthesized the Eu(TTA)3Phen complex and present herein a detailed study of its photophysics. The investigations encompass samples dispersed in poly(vinyl alcohol) and in ethanol in order to explore the versatile applicability of these lanthanide-based materials. Details upon the interaction between Eu, TTA, and the Phen ligands are revealed by Fourier transform infrared and UV-visible absorption, complemented by steady state and temporally resolved emission studies, which provide evidence of an efficient energy transfer from the organic ligands to the central Eu(3+) ion. The material produces efficient emission even under sunlight exposure, a feature pointing toward suitability for luminescent solar concentrators and UV light sensing, which is demonstrated for intensities as low as 200 nW/cm(2). The paper further promotes the complexs capability to be used as luminescence-based temperature sensor demonstrated by the considerable emission intensity changes of ∼4.0% per K in the temperature range of 50-305 K and ∼7% per K in the temeperature range 305-340 K. Finally, increasing the optical excitation causes both spontaneous emission amplification and emission peak narrowing in the Eu(TTA)3Phen complex dispersed in poly(vinyl alcohol) - features indicative of stimulated emission. These findings in conjunction with the fairly large stimulated emission cross-section of 4.29 × 10(-20) cm(2) demonstrate that the Eu(TTA)3Phen complex dispersed in poly(vinyl alcohol) could be a very promising material choice for lanthanide-polymer based laser architectures.

Host matrix impact on Er3+ upconversion emission and its temperature dependence

By synthesizing Y(1.9−2x)Yb0.1Er2xO3, Y(0.95−x)Yb0.05ErxVO4 and Y(0.95−x)Yb0.05ErxPO4 phosphors, with phonon frequency maxima at 560, 826 and 1050 cm−1, respectively, we present the impact of phonon energy and crystal structure of the host matrix on upconversion and temperature sensing behavior. The spectral upconversion characteristics of all three phosphors reveal noticeable differences. The temperature sensing studies reveal that the phosphors have maximum sensitivity at ∼490 K, which is found to be highest (0.0105 K−1) in Y0.947Yb0.05Er0.003VO4 followed by Y1.894Yb0.1Er0.006O3 and Y0.947Yb0.05Er0.003PO4 phosphors. We found that the temperature sensitivity basically depends on the intensity ratio of two thermally coupled emission bands, 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2, of Er3+. Further, the intensity ratio depends on phonon energy of the host lattice, crystal structure, surface quenching centers and the temperature dependence of non-radiative decay rate.

A strategy to achieve efficient dual-mode luminescence in lanthanide-based magnetic hybrid nanostructure and its demonstration for the detection of latent fingerprints

We 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 6-8nm. 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.

An assembly and interaction of upconversion and plasmonic nanoparticles on organometallic nanofibers: enhanced multicolor upconversion, downshifting emission and the plasmonic effect

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.

Silver nanoparticles embedded hybrid organometallic complexes: Structural interactions, photo-induced energy transfer, plasmonic effect and optical thermometry

A novel hybrid material comprising of two β-diketonate complexes, Tb(ASA)3Phen (TAP) and Eu(TTA)3Phen (ETP), has been synthesized and studied its photo-physics, energy transfer and optical thermometry applications. Using XRD and FTIR spectra, it has been demonstrated that both the complexes maintain their core entity and show weak interaction between them in the hybrid complex (HC). The TEM images show the coating of ETP layers over nano-fibrous TAP and further, embedded with Ag nanoparticles over HC. It has been observed that ligands (Phen, TTA as well as ASA) absorb the UV radiation and undergoes single to triplet via intersystem crossing transitions by transferring its excitation energy to central lanthanide ions (Eu3+ and Tb3+). In this strategy, an efficient energy transfer between two different species i.e. ASA to Tb3+ (in TAP complex) to Eu+3 ions (of ETP complex) has also been observed. To probe and verify the energy transfer mechanism, life time measurements have been carried out. The life time of Tb3+ decreases in HC as compared with TAP, whereas the life time of Eu3+ increases in HC as compared with ETP. The addition of silver nanoparticles (AgNPs) again enhances the fluorescence intensity of Eu3+ emission band. The prepared HC has further been demonstrated for ambient range temperature (295-365 K) sensing and the sensitivity of the material is found to be 6.8% change in signal per K. The strong optical property and non-toxic nature of this HC is useful in biomedical, bio-imaging and energy harvesting applications.A novel hybrid material comprising of two β-diketonate complexes, Tb(ASA)3Phen (TAP) and Eu(TTA)3Phen (ETP), has been synthesized and studied its photo-physics, energy transfer and optical thermometry applications. Using XRD and FTIR spectra, it has been demonstrated that both the complexes maintain their core entity and show weak interaction between them in the hybrid complex (HC). The TEM images show the coating of ETP layers over nano-fibrous TAP and further, embedded with Ag nanoparticles over HC. It has been observed that ligands (Phen, TTA as well as ASA) absorb the UV radiation and undergoes single to triplet via intersystem crossing transitions by transferring its excitation energy to central lanthanide ions (Eu3+ and Tb3+). In this strategy, an efficient energy transfer between two different species i.e. ASA to Tb3+ (in TAP complex) to Eu+3 ions (of ETP complex) has also been observed. To probe and verify the energy transfer mechanism, life time measurements have been carried out. The life time o...