Chanchal Hazra

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 ]

Enhancing the color purity of the green upconversion emission from Er3+/Yb3+-doped GdVO4 nanocrystals via tuning of the sensitizer concentration

Here we report on the enhancement of the intensity of the green/red emission ratio in Er3+/Yb3+-doped GdVO4 nanocrystals obtained via the upconversion process. The nanocrystals were synthesized using a sol–gel process followed by a solid-state reaction. A series of samples bearing different sensitizer ion (Yb3+) concentrations were studied and characterized. Tripositive erbium (Er3+)-doped GdVO4 shows two strong emissions in the green region near 525 and 550 nm while a relatively weak red emission is centred at 660 nm. A 5-fold increase in the intensity of the green/red emission ratio is observed for the Er3+/Yb3+-doped GdVO4 sample co-doped with 20 mol% Yb3+ concentration in comparison to a similar sample without any Yb3+. This suggests a corresponding increase in the color purity of the green emission and as a consequence, this material would be an interesting candidate as a phosphor for display and LED applications.

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]

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.

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.

3,5-Dinitrobenzoic Acid-Capped Upconverting Nanocrystals for the Selective Detection of Melamine

In this Research Article, we report for the first time the use of upconverting nanoparticles to detect melamine up to nanomolar concentration. Detection of melamine is important as it is one of the adulterant in protein rich food products due to its high nitrogen content. In this work, we have shown how the electron deficient 3,5-dinitrobenzoic acid (DNB)-coated Er/Yb-NaYF4 nanocrystals can specifically bind to electron rich melamine and alter the upconverting property of the nanocrystals. This selective binding led to the quenching of the upconversion emission from the nanocrystals. The high selectivity is verified by the addition of various analytes similar in structure with that of melamine. In addition, the selective quenching of the upconversion emission is reversible with the addition of dilute acid. This process has been repeated for more than five cycles with only a slight decrease in the sensing ability. The study was also extended to real milk samples, where the milk adulterated with melamine quenches the emission intensity of the DNB coated NaYF4:Er/Yb nanocrystals, whereas hardly any change is noted for the unadulterated milk sample. The high robustness and the sharp emission peaks make Er(3+)/Yb(3+)-doped NaYF4 nanocrystals a potential melamine sensing material over other organic fluorophores and nanocrystals possessing broad emissions.

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.

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.