Morphology control, luminescence and energy transfer properties of NaCeF4 and NaCeF4:Tb3+/Yb3+ nanocrystals

Tuning Luminescence of Lanthanide-Doped Upconversion Nanoparticles through Simultaneous Binary Cation Exchange

Dual-mode luminescent nanomaterials have outstanding performance in biosensing and multistage anticounterfeiting. Herein, we report the tuning of optical attributes of lanthanide-doped nanoparticles (NPs) via simultaneous binary cation exchange. We show that cation exchange of NaYF₄:Yb/Er (18/2 mol %)@NaLnF₄ (Ln = Y and Gd) NPs with a combination of Ce³⁺ and Tb³⁺ enables the resultant nanoparticles to exhibit both upconversion and downshifting emissions upon excitation at 980 and 254 nm, respectively. We find that in addition to introducing downshifting emission attributes, the use of Tb³⁺ ions allows conservation of the integrity of the parent core@shell NPs by decreasing the dissociation tendency caused by Ce³⁺ ions during the cation exchange. The upconversion color output can be tuned from green to red and blue by changing lanthanide combinations in the core NPs. This work not only provides an effective strategy for the optical tuning of lanthanide-doped NPs but also builds a platform for probing the difference in the reactivity nature of lanthanides.

PEI functionalized NaCeF4:Tb3+/Eu3+ for photoluminescence sensing of heavy metal ions and explosive aromatic nitro compounds

This work reports an eco-friendly hydrothermal approach for the synthesis of hexagonal NaCeF4:Tb3+/Eu3+ nanophosphors. The phase, morphology and optical properties were characterized by Powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy and photoluminescence (PL) spectroscopy respectively. Herein, the as-synthesized nanophosphor was functionalized with amine rich polyethylenimine (PEI) resulting in development of a luminescent nanoprobe bearing dual sensing functions for hazardous nitroaromatics and heavy metal ions. The strong photoluminescence emission of Eu3+ ions was selectively quenched upon addition of toxic analytes at concentrations from 10 to 100 ppm due to complex formation between the analytes and PEI functionalized nanostructure. The synthesized nanomaterial shows sharp emission peaks at 493, 594, 624, 657 and 700 nm. Significantly, the peak at 594 nm shows a noticeable quenching effect on addition of toxic analytes to the aqueous solution of the nanocrystals. The nanophosphors are sensitive and efficient for the PA and Fe3+ ion detection with an LOD of 1.32 ppm and 1.39 ppm. The Stern-Volmer (SV) quenching constant (K SV) is found to be 2.25 × 105 M-1 for PA and 3.8 × 104 M-1 for Fe3+ ions. The high K SV value and low LOD suggest high selectivity and sensitivity of the nanosensor towards PA and Fe3+ ions over other analytes. Additionally, a reduced graphene oxide and nanophosphor based nanocomposite was also synthesized to investigate the role of energy transfer involving delocalized energy levels of reduced graphene oxide in regulating the luminescence properties of the nanophosphor. It was observed that PEI plays central role in inhibiting the quenching effect of reduced graphene oxide on the nanophosphor.

Hydrothermal syntheses, luminescent properties, and temperature sensing of monodisperse Tb-doped NaCeF4 nanocrystals

Monodisperse Tb-doped NaCeF₄ nanocrystals were synthesized via a hydrothermal method. The morphology, and room temperature and temperature dependent luminescent properties were investigated. Excited at 254 nm, the emissions of Ce³⁺ at 270-370 nm and those of Tb³⁺ at 475-700 nm can be observed. The strongest visible emission was observed in NaCeF₄:20 at% Tb with a quantum yield of 49%. The efficiency of energy transfer from Ce³⁺ to Tb³⁺ increases with the Tb³⁺ doping concentration and reaches 95% for NaCeF₄:30 at% Tb. The ratio of Tb³⁺ emission to Ce³⁺ emission is sensitive to temperature, and the relative sensitivity was calculated to be 1.0% °C^-1 at 60 °C. The mechanisms for this thermal dependence were analyzed in terms of non-radiative relaxation and energy migration.

An efficient down conversion luminescencent probe based on a NaGdF4:Eu3+/Ce3+ nanophosphor for chemical sensing of heavy metal ions (Cd2+, Pb2+ and Cr3+) in waste water

Eu³⁺ doped and Eu³⁺/Ce³⁺ co-doped NaGdF₄ nanophosphors are fabricated via a facile hydrothermal route. The codoped counterpart is demonstrated for efficient photoluminescence sensing of heavy metal ions (Cd²⁺, Pb²⁺ and Cr³⁺) present in industrial effluents.

Photonic structuring improves the colour purity of rare-earth nanophosphors

Nanophosphor integration in an optical cavity allows unprecedented control over both the chromaticity and the directionality of the emitted light, without modifying the chemical composition of the emitters or compromising their efficiency. Our approach opens a route towards the development of nanoscale photonics based solid state lighting.

Fixed-diameter upconversion nanorods with controllable length and their interaction with cells

A series of NaYF₄: Yb, Er upconversion nanorods with fixed diameter and controllable length were synthesized by the injection of sodium trifluoroacetate (CF₃COONa) mixed with potassium trifluoroacetate (CF₃COOK) precursor into a heated solution of ligand. We found that with the increased percentage of CF₃COOK, the length of resultant nanorods was increased from ∼40 nm to ∼200 nm whilst the diameter was kept in a narrow range of 37-42 nm. The elongation of nanorods was attributed to the specific absorption of sodium oleate on the prismatic facets, and the integration of potassium ions into the lattice as well. We further found that the elongated length affected the relative fluorescence intensity between red and green emission. More importantly, with fixed diameter, the cellular uptake of nanorods was found decreasing with the increase of their length. Meanwhile the decrease of diameter resulted in an increased cellular uptake. These results were attributed to both specific surface area and possibly varied contacting angle between nanorods and cell membrane. The current work not only suggested a synthetic method for the precise control of upconversion nanorods, but also shed light on the design of nanocrystals for cell-related biomedical applications.

Two-step synthesis of hole structure bastnasite (RECO3F RE = Ce, La, Pr, Nd) sub-microcrystals with tunable luminescence properties

A two-step synthetic route using RE(OH)CO₃ colloid spheres as the sacrificial template was designed to prepare monodisperse, pure bastnasite (RECO₃F: RE = Ce, La, Pr, Nd) with a hole structure for the first time.

Growth phase diagram and upconversion luminescence properties of NaLuF4:Yb3+/Tm3+/Gd3+ nanocrystals

Relationships between the phase, reaction time, and UCL intensity of NaLuF₄ nanocrystals are investigated.

Nanostructured magnetic nanocomposites as MRI contrast agents

Magnetic resonance imaging (MRI) has become an integral part of modern clinical imaging due to its non-invasiveness and versatility in providing tissue and organ images with high spatial resolution. With the current MRI advancement, MRI imaging probes with suitable biocompatibility, good colloidal stability, enhanced relaxometric properties and advanced functionalities are highly demanded. As such, MRI contrast agents (CAs) have been an extensive research and development area. In the recent years, different inorganic-based nanoprobes comprising inorganic magnetic nanoparticles (MNPs) with an organic functional coating have been engineered to obtain a suitable contrast enhancement effect. For biomedical applications, the organic functional coating is critical to improve colloidal stability and biocompatibility. Simultaneously, it also provides a building block for generating a higher dimensional secondary structure. In this review, the combinatorial design approach by a self-assembling pre-formed hydrophobic inorganic MNPs core (from non-polar thermolysis synthesis) into various functional organic coatings (e.g. ligands, amphiphilic polymers and graphene oxide) to form water soluble nanocomposites will be discussed. The resultant magnetic ensembles were classified based on their dimensionality, namely, 0-D, 1-D, 2-D and 3-D structures. This classification provides further insight into their subsequent potential use as MRI CAs. Special attention will be dedicated towards the correlation between the spatial distribution and the associated MRI applications, which include (i) coating optimization-induced MR relaxivity enhancement, (ii) aggregation-induced MR relaxivity enhancement, (iii) off-resonance saturation imaging (ORS), (iv) magnetically-induced off-resonance imaging (ORI), (v) dual-modalities MR imaging and (vi) multifunctional nanoprobes.

Multifunctional MWCNTs–NaGdF4:Yb3+,Er3+,Eu3+ hybrid nanocomposites with potential dual-mode luminescence, magnetism and photothermal properties

Novel multifunctional MWCNTs–NaGdF₄:Yb³⁺,Er³⁺,Eu³⁺ hybrid nanocomposites can simultaneously take advantage of up- and down-conversion luminescence, magnetism and photothermal properties.