Tuhin Samanta

A Highly Efficient UV–Vis–NIR Active Ln3+-Doped BiPO4/BiVO4 Nanocomposite for Photocatalysis Application

In this Article, we report the synthesis of Ln(3+) (Yb(3+), Tm(3+))-doped BiPO4/BiVO4 nanocomposite photocatalyst that shows efficient photocatalytic activity under UV-visible-near-infrared (UV-vis-NIR) illumination. Incorporation of upconverting Ln(3+) ion pairs in BiPO4 nanocrystals resulted in strong emission in the visible region upon excitation with a NIR laser (980 nm). A composite of BiPO4 nanocrystals and vanadate was prepared by the addition of vanadate source to BiPO4 nanocrystals. In the nanocomposite, the strong blue emission from Tm(3+) ions via upconversion is nonradiatively transferred to BiVO4, resulting in the production of excitons. This in turn generates reactive oxygen species and efficiently degrades methylene blue dye in aqueous medium. The nanocomposite also shows high photocatalytic activity both under the visible region (0.010 min(-1)) and under the full solar spectrum (0.047 min(-1)). The results suggest that the photocatalytic activity of the nanocomposite under both NIR as well as full solar irradiation is better compared to other reported nanocomposite photocatalysts. The choice of BiPO4 as the matrix for Ln(3+) ions has been discussed in detail, as it plays an important role in the superior NIR photocatalytic activity of the nanocomposite photocatalyst.

C-dot sensitized Eu3+ luminescence from Eu3+-doped LaF3–C dot nanocomposites

Very strong Eu3+ luminescence is achieved via sensitization by carbon dots (C-dots) in Eu3+-doped LaF3–C-dot nanocomposites for the first time. This energy transfer via C-dots leads to the broadband excitation of Eu3+ ions which can have potential use in phosphor based LEDs.

A resonance energy transfer approach for the selective detection of aromatic amino acids

In this article, we report for the first time the use of Ln3+-doped nanocrystals to detect aromatic amino acids (AAs) up to nanomolar concentration. Detection of AAs is important for several reasons. For instance, increased levels of AAs are detected in the early phase of gastric carcinogenesis in gastric juice samples. In this work, we have shown that the highly efficient energy transfer between Ce3+ and Tb3+ ions in Ce3+/Tb3+-doped CaMoO4 nanocrystals is selectively altered by the addition of AAs, thus providing a simple resonance energy transfer (RET) approach to detect AAs in the nanomolar (nM) range. This is achieved as the absorption spectrum of AAs overlaps with the emission spectrum of the Ce3+/Tb3+-doped CaMoO4 nanocrystals, thus reducing the energy transfer efficiency between the Ce3+ and Tb3+ ions. This selective energy transfer process leads to the quenching of the Tb3+ emission from the nanocrystals. The high selectivity was verified by the addition of essential or non-essential amino acids, and some metal ions and molecules that generally coexist with AAs in our body. Moreover, the selective quenching of the Tb3+ ion emission can be easily reversed by the addition of ninhydrin; 90% of the initial luminescence intensity is recovered during the reversal process. This process was repeated for more than five cycles with only a slight decrease in the sensing ability. The study was also extended to 2D surfaces where the nanocrystals are strongly attached to a positively charged surface, which, upon dipping into the AA solution, leads to the quenching of the luminescence exhibited by the Tb3+ ions. The signal can be easily recovered after ninhydrin treatment.

Photoluminescence and photocatalytic activity of monodispersed colloidal “ligand free Ln3+-doped PbMoO4 nanocrystals”

In this article, we have shown a synthetic strategy to prepare ligand-free colloidal Eu3+-doped PbMoO4 nanocrystals that form a stable dispersion in polar solvents. The surface of the nanocrystals is designed to have excess residual ions (Pb2+ or MoO42−) compared to the counter-ionic species, thereby providing a partially charged nanocrystal surface. These charged nanocrystal surfaces cause electrostatic repulsion, providing colloidal stability in polar solvents. Microscopic measurements suggest the formation of spherical shaped nanocrystals with an average size of 10 nm. Upon UV excitation, aqueous dispersions of the Eu3+-doped PbMoO4 nanocrystals display intense red emission characteristic of Eu3+ ions. Furthermore, under UV irradiation, the nanocrystals exhibit strong photocatalytic activity, which is verified from the degradation of rhodamine B dye. The rhodamine B dye is significantly degraded by ∼70% under UV illumination within 3 h at pH 5.5. The strong luminescence efficiency and photocatalytic activity make the water dispersible Ln3+-doped PbMoO4 nanocrystals a potential material for dual applications like luminescence and photocatalysts.

Design of Lanthanide-Doped Colloidal Nanocrystals: Applications as Phosphors, Sensors, and Photocatalysts

The unique optical characteristics of lanthanides (Ln3+) such as high color purity, long excited-state lifetimes, less perturbation of excited states by the crystal field environment, and the easy spectral conversion of wavelengths through upconversion and downconversion processes have caught the attention of many scientists in the recent past. To broaden the scope of using these properties, it is important to make suitable Ln3+-doped materials, particularly in colloidal forms. In this feature article, we discuss the different synthesis strategies for making Ln3+-doped nanoparticles in colloidal forms, particularly ways of functionalizing hydrophobic surfaces to hydrophilic surfaces to enhance their dispersibility and luminescence in aqueous media. We have enumerated the various strategies and sensitizers utilized to increase the luminescence of the nanoparticles. Furthermore, the use of these colloidal nanoparticle systems in sensing application by the appropriate selection of capping ligands has been discussed. In addition, we have shown how the energy transfer efficiency from Ce3+ to Ln3+ ions can be utilized for the detection of toxic metal ions and small molecules. Finally, we discuss examples where the spectral conversion ability of these materials has been used in photocatalysis and solar cell applications.

Host sensitized intense infrared emissions from Ln3+ doped GdVO4 nanocrystals: ranging from 950 nm to 2000 nm

In this communication we report the observation of intense near infrared (NIR) emissions in the 900 nm to 2000 nm range from colloidal water dispersible lanthanide (Ln3+) doped GdVO4 nanocrystals (Ln = Sm3+, Nd3+, Dy3+, Tm3+, Er3+ and Ho3+). Observing strong NIR emission, particularly from aqueous medium, is a challenge as the luminescence is more prone to non-radiative relaxation. The observed intense NIR emissions from Ln3+-doped GdVO4 nanocrystal ions are attributed to the efficient sensitization of the Ln3+ excited levels via a GdVO4 host matrix. The GdVO4 matrix shows intense and broad absorbance in the ultraviolet (UV) region resulting from the charge transfer from the 2p orbital of oxygen to the d orbital of V5+ ions of the VO4− group. Upon UV excitation, GdVO4 absorbs the light and efficiently transfers the energy to the excited state of the Ln3+ ions, which emit in the NIR region. The calculated energy transfer efficiencies for most of the studied Ln3+ ions are about 90%. In fact, the observed enhancement in the NIR emission intensity varies between 3 (for Sm3+) and 53 fold (Nd3+) compared to direct excitation. The combination of high aqueous stability and intense NIR emission can be advantageous for applications like NIR bioimaging. In addition, these colloidal nanocrystals can easily be incorporated into sol–gel or glass matrices for the fabrication of devices such as optical amplifiers, fiber optics for telecommunications, etc.

Temperature effects on the hydrophobic force between two graphene-like surfaces in liquid water

Water-mediated, effective, long-range interaction between two hydrophobic surfaces immersed in water is of great importance in natural phenomena. We perform the molecular dynamics simulations to investigate the effect of temperature on the attractive force between two graphene-like hydrophobic surfaces in SPC/E water. We systematically calculate the force between two hydrophobic surfaces at different inter-wall separations (d) and subsequently determine the correlation lengths at different temperatures. A significant change in the strength of the attractive hydrophobic force is observed with the variation of temperature. The correlation length of effective hydrophobic force increases on lowering the temperature. We also examine the temperature effects on the behavior of confined water molecules by computing the density and orientational profiles. The analyses of these profiles suggest that the layering of water molecules induced by surfaces decreases with increase in temperature of the system. Critical dewetting distance (

Dynamics of a binary mixture of non-spherical molecules: Test of hydrodynamic predictions

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