Shyam Sarkar

Sub‐5 nm Ln3+‐doped BaLuF5 Nanocrystals: A Platform to Realize Upconversion via Interparticle Energy Transfer (IPET)

detection and sensing, [ 4 ] solar cells, [ 5 ] etc. These upconverting nanomaterials are generally composed of lanthanide (Ln 3 + ) ions which are spatially distributed in a suitable host matrix. [ 6 ] The Ln 3 + ions possess interesting optical characteristics, such as sharp emissions, and long luminescence life times, and exhibit multiple emissions spanning a wide region (UV to NIR), which are exploited in several applications like developing phosphors, biomarkers, and optoelectronic devices, to name only a few. [ 7 ]

Bright Luminescence from Colloidal Ln3+‐Doped Ca0.72Y0.28F2.28 (Ln=Eu, Tm/Yb) Nanocrystals via Both High and Low Energy Radiations

The interest in lanthanide (Ln)-doped luminescent nanomaterials is continuously growing from a scientific viewpoint. This interest is largely credited to their intra-4f transitions, which are quite sharp due to the shielding of the 4f orbitals by the outer 5s and 5p orbitals. Although forbidden in nature, these sharp transitions are exploited for several applications, such as in the development of novel phosphors for LEDs and display applications, laser crystals, optoelectronic devices, etc. In addition, some Ln ions when doped in a suitable host matrix display the ability to convert low energy near infrared (NIR) radiation into high energy visible radiation, a process known as upconversion. This ability to produce anti-Stokes emission is largely due to the presence of multiple energy levels and their longer life times. The excitation radiation being silent to tissues is envisioned to replace organic fluorophores for biomaker applications. The quantum efficiencies of both Stokes and anti-Stokes emissions largely depend on the host matrix in which the Ln ions are incorporated. Various host matrices have been reported but fluorides are quite interesting due to their low phonon energy (350–400 cm ), which consequently minimizes the non-radiative transitions. Moreover, there are several synthetic methods developed to prepare high quality fluoride nanocrystals. To name a few, Ln-doped, NaYF4, LiYF4, LaF3, etc., have been prepared in colloidal forms. [6]

Strong Stokes and Upconversion Luminescence from Ultrasmall Ln3+-Doped BiF3 (Ln=Eu3+, Yb3+/Er3+) Nanoparticles Confined in a Polymer Matrix

Heavy metal fluorides like BiF3 as a host for lanthanide ions are of interest as bismuth is the only heavy metal that is nontoxic. In this work, we report the synthesis of highly water-dispersible ultrasmall BiF3 nanoparticles about 6 nm in size within a poly(vinyl pyrrolidone) matrix by a hydrothermal method. Microscopy analysis reveals that the nanoparticles are well separated and confined within the polymer network. These nanoparticles were found to be excellent hosts for lanthanide (Ln(3+)) ions. Through suitable Ln(3+) doping, BiF3 exhibits strong emissions in the visible region upon both UV and near infrared (NIR) excitations. The non-toxicity of both bismuth and PVP can be advantageous for the potential use of BiF3 nanoparticles in drug delivery and bioimaging.

Highly luminescent colloidal Eu(3)+-doped KZnF(3) nanoparticles for the selective and sensitive detection of Cu(II) ions.

This article describes a green synthetic approach to prepare water dispersible perovskite-type Eu3+-doped KZnF3 nanoparticles, carried out using environmentally friendly microwave irradiation at low temperature (85 8C) with water as a solvent. Incorporation of Eu3+ ions into the KZnF3 matrix is confirmed by strong red emission upon ultraviolet (UV) excitation of the nanoparticles. The nanoparticles are coated with poly(acrylic acid) (PAA), which enhances the dispersibility of the nanoparticles in hydrophilic solvents. The strong red emission from Eu3+ ions is selectively quenched upon addition of CuII ions, thus making the nanoparticles a potential CuII sensing material. This sensing ability is highly reversible by the addition of ethylenediaminetetraacetic acid (EDTA), with recovery of almost 90% of the luminescence. If the nanoparticles are strongly attached to a positively charged surface, dipping the surface in a CuII solution leads to the quenching of Eu3+ luminescence, which can be recovered after dipping in an EDTA solution. This process can be repeated for more than five cycles with only a slight decrease in the sensing ability. In addition to sensing, the strong luminescence from Eu3+-doped KZnF3 nanoparticles could be used as a tool for bioimaging.

Enhanced quantum efficiency for Dy3+ Emissions in water dispersible PbF2 nanocrystals

PbF2 nanocrystals found to be a better host for Dy3+ ions to exhibit better quantum efficiency. The optimum dopant concentration is found to be higher than that observed in several bulk materials. The nanocrystals are rendered water dispersible by coating poly(acrylic acid) over their surface.

Selective reduction of visible upconversion emissions induced by Bi3+ in Tm3+/Yb3+-doped Y0.89−xBixVO4 microcrystals

In this article we have shown that the intensity ratio of near infrared (NIR) to blue upconversion emission from Tm3+ ions can be enhanced up to 800 times by simple control of the concentrations of Bi3+/Y3+ in Tm3+(0.01)/Yb3+(0.10)-doped Y0.89−xBixVO4 (x = 0 to 0.89) microcrystals. The intensity of the strong blue emission occurring near 475 nm due to the 1G4→3H6 transition is selectively reduced upon bismuth doping, while the intensity of the NIR emission at 800 nm (3H4→3H6) is hardly affected. The enhanced NIR/blue emission intensity achieved via the upconversion process is advantageous in reducing the background scattering, and consequently increases the contrast in the bio-imaging applications. Several control experiments were performed to unravel the role of Bi3+ ions in the reduction of the blue emission intensity. An energy transfer mechanism involving Tm3+, Bi3+ and Yb3+ ions is proposed for the preferential reduction in intensity of the blue emission. All microcrystal samples were completely characterized using XRD, Raman and photoluminescence methods.

Eu3+ ions as an optical probe to follow the growth of colloidal ZnO nanostructures

The colloidal growth of ZnO exhibits interesting dynamics, which is generally probed using absorbance measurements. Here, we have shown that the sharp luminescent signals from the Eu(3+) ions act as a potential luminescent spectral probe to follow the growth of ZnO nanostructures. The Eu(3+)-doped ZnO nanocrystals were synthesized by a colloidal method. The asymmetry ratio calculated from the Eu(3+) emission intensity peaks ((5)D0 → (7)F2/(5)D0 → (7)F1) gradually decrease with the increase in the size of the ZnO nanostructures. This is attributed to the increase in the surface related defects as the size of the ZnO nanocrystals is increased. The above result is supported by controlling the growth of the ZnO nanocrystals with capping ligands. The Eu(3+) luminescence intensity hardly is affected upon ligand capping. Additional experiments such as lifetime measurements and photocatalytic activity of ZnO strongly indicate that Eu(3+) can be used as a potential tool to follow the growth of colloidal ZnO nanostructures. We believe the study can be extended to understand the growth mechanism of several other colloidal nanostructures.