Precisely tailored shell thickness and Ln3+ content to produce multicolor emission from Nd3+-sensitized Gd3+-based core/shell/shell UCNPs through bi-directional energy transfer.

Lanthanide (Ln3+)-doped upconversion nanoparticles (UCNPs) have been paid great attention as multiplexing agents due to their numerous uses in biological and clinical applications such as bioimaging and magnetic resonance imaging (MRI), to name a few. To achieve efficient multicolor emission from UCNPs under single 808 nm excitation and avoid detrimental cross-relaxations between the Ln3+ activator ions (positioned in either the core and/or shell in the core/shell), it is essential to design an adequate nanoparticle architecture. Herein, we demonstrate the tailoring of multicolor upconversion luminescence (UCL) from Nd3+-sensitized Gd3+-based core/shell/shell UCNPs with an architecture represented as NaGdF4:Tm3+(0.75)/Yb3+(40)/Ca2+(7)/Nd3+(1)@NaGdF4:Ca2+(7)/Nd3+(30)@NaGdF4:Yb3+(40)/Ca2+(7)/Nd3+(1)/Er3+(X = 1, 2, 3, 5, 7) [hereafter named CSS (Er3+ = 1, 2, 3, 5 and 7 mol%)]. Such UCNPs can be excited at a single wavelength (∼808 nm) without generation of any local heat. Incorporation of substantial Nd3+-sensitizers with an appropriate concentration in the middle layer allows efficient harvesting of excitation light which migrates bi-directionally across the core/shell interfaces in sync to produce blue emission from Tm3+ (activator) ions in the core as well as green and red emission from Er3+ (activator) ions in the outermost shell. Introduction of Ca2+ lowers the local crystal field symmetry around Ln3+ ions and subsequently affects their intra 4f-4f transition probability, thus enhancing the upconversion efficiency of the UCNPs. By simple and precise control of the shell thickness along with tuning the content of Ln3+ ions in each domain, multicolor UCL can be produced, ranging from blue to white. We envision that our sub-20 nm sized Nd3+-sensitized Gd3+-based UCNPs are not only potential candidates for a variety of multiplexed biological applications (without impediment of any heating effect), but also can act as MRI contrast agents in clinical diagnosis.

A Highly Efficient UV-Vis-NIR Active Ln(3+)-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.

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.

Bilayer stabilized Ln³âº-doped CaMoO4 nanocrystals with high luminescence quantum efficiency and photocatalytic properties.

In this article, we discuss the microwave synthesis of sodium dodecyl sulphate (SDS) stabilized Ln(3+)-doped CaMoO4 nanocrystals (Ln(3+) = Eu(3+), Er(3+)/Yb(3+)). The nanocrystals are quite monodispersed with an average size close to 100 nm. FTIR and TGA analyses suggest strong binding of the SDS molecules to the CaMoO4 nanocrystals surface. The high dispersibility of the nanocrystals in water implies that SDS stabilizes the nanocrystals as a bilayer structure. The SDS coating also assists in the easy dispersion of the nanocrystals in toluene without any additional surface chemistry. The Eu(3+) ions doped in the CaMoO4 nanocrystals display very strong red luminescence with a quantum yield close to 40%. Under 980 nm excitation, Er(3+)/Yb(3+)-doped CaMoO4 nanocrystals display Er(3+) emissions at 550 and 650 nm. In addition, interestingly, a NIR peak at around 833 nm is observed, which occurred via a three photon process. Furthermore, the CaMoO4 nanocrystals exhibit photocatalytic activity which is studied through the degradation of Rhodamine B (RhB) dye in neutral conditions. The RhB dye is significantly degraded by ~80% under UV illumination within 4 h and the rate of degradation is comparable to that observed for well known ZnO nanoparticles. The high luminescence quantum efficiency and strong photocatalytic activity of the Ln(3+)-doped CaMoO4 nanocrystals make them a potential material for dual applications such as bio-imaging and photocatalysis.

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.

Scaling down the size of BaLnF5 nanocrystals (Ln = La, Gd, and Lu) with the Ln3+ size.

Monodispersed Yb(3+)(20%)/Er(3+)(2%)-doped BaLnF(5) (Ln = La, Gd, Lu) nanocrystals were synthesized by a thermal decomposition method. The study reveals that the size of the nanocrystals scales down with the Ln(3+) size without affecting the phase and shape of the nanocrystals. This is supported by the microscopic and optical properties.

Ricinoleic Acid-Capped Upconverting Nanocrystals: An Ideal Capping Ligand to Render Nanocrystals Water Dispersible.

Cap in hand: Ricinoleic acid (RA) replaces oleic acid as capping ligand in the synthesis of upconverting nanocrystals in the size range of 10 nm. The presence of hydroxyl groups near the double bond in RA is advantageous in hydroxylation of the bond, and the size of the nanocrystals is preserved. The small size, high water dispersibility, and strong upconversion from the nanocrystals could be utilized in sensing and bioimaging applications.