Dual mode emissions with enhanced green up-conversion luminescence by Gd3+ doping and down-conversion from Eu3+ in NaMnF3:Yb,Er@NaGdF4:Eu

NaMnF3:Yb,Er and NaMnF3:Yb,Er@NaGdF4:xEu (x = 0, 0.3, 0.6, and 0.9) samples were synthesized by a simple hydrothermal method. The as-obtained NaMnF3:Yb,Er particles show a single red emission under the irradiation of infrared light (980 nm), due to the energy exchange transfer process between Mn2+ ions and Er3+ ions. Notably, further growth of NaGdF4:Eu on the basis of NaMnF3:Yb,Er enhanced the green up-conversion luminescence of Er3+ ions, which gradually shifted from red to green with the increase of the Gd3+ ion doping amount. In addition, NaMnF3:Yb,Er@NaGdF4:Eu exhibits red color under ultraviolet excitation (397 nm). These results provide a possible means for controlling the luminescence properties of the lanthanide doped up-conversion system. The luminescent film synthesized with NaMnF3:Yb,Er@NaGdF4:Eu can show different luminescent colors under different light irradiation (near infrared and ultraviolet), which indicates that they have potential applications in multi-mode anti-counterfeiting.

Fabrication of NaYF4:Yb3+,Tm3+-modified Ag nanocubes with upconversion luminescence and photothermal conversion properties

Herein, uniform Ag nanocube@NaYF₄:Yb³⁺,Tm³⁺ multifunctional nanocomposites were constructed by a facile synthetic strategy. Following the successful synthesis of Ag nanocubes, cubic phase NaYF₄:Yb³⁺,Tm³⁺ upconversion luminescent nanocrystals were modified on the surface of the Ag nanocubes, enhanced the mutual assistance of energy and versatility of the materials. Upon irradiation with a near-infrared laser, the nanocomposites exhibited excellent upconversion fluorescence and good photothermal conversion capability. Furthermore, the potential biological applications and biosafety of the Ag@NaYF₄:Yb³⁺,Tm³⁺ nanocomposites were also demonstrated; the obtained nanocomposites could achieve a good bactericidal performance and photothermal treatment of cancer cells, and they could be potentially applied in the biomedical field as a promising agent. Furthermore, this method provides a facile approach for synthesizing a multifunctional nanocomposite with different properties.

Ag nanocubes@NaYF₄:Yb³⁺,Tm³⁺ multifunctional nanocomposites with florescence and photothermal ability are fabricated by a facile strategy, which enhance the mutual assistance of energy and biological application.

Mutual energy transfer luminescent properties in novel CsGd(MoO4)2:Yb3+,Er3+/Ho3+ phosphors for solid-state lighting and solar cells

In this work, we prepared a novel kind of Yb3+,Er3+/Ho3+ co-doped CsGd(MoO4)2 phosphors with a different structure from the reported ALn(MoO4)2 (A = Li, Na or K; Ln = La, Gd or Y) compounds using a high-temperature solid-state reaction method. X-ray diffraction showed that the as-prepared samples had a pure phase. Based on the efficient energy transfer from Yb3+ to Er3+/Ho3+, the up-conversion (UC) luminescence of the optimal CsGd(MoO4)2:0.30Yb3+,0.02Er3+ sample showed intensely green light with dominant emission peaks at 528 and 550 nm corresponding to Er3+ transitions 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2, respectively, as well as a weak emission peak originating from 4F9/2 → 4I15/2 at 671 nm, under 975 nm laser excitation. The CsGd(MoO4)2:Yb3+,Ho3+ samples mainly displayed two emission bands around 540 and 660 nm together with a negligible one at 755 nm, which corresponded to Ho3+ transitions 4F4,5F2 → 5I8, 5F5 → 5I8 and 4F4,5F2 → 5I7, respectively, under 975 nm laser excitation. With increasing Yb3+ concentration in CsGd(MoO4)2:Yb3+,Ho3+ phosphors, the emission color could be tuned from orange red to light yellow due to the large energy gap between levels 4F4,5F2 and 5F5. In addition, the CsGd(MoO4)2:Yb3+,Er3+ showed green light under 376 nm UV irradiation similar to that upon 975 nm laser excitation. However, the emissions for CsGd(MoO4)2:Yb3+,Ho3+ samples under 358 nm UV or 449 nm blue excitation showed dominant emission peaks at 540 nm and weak 660 nm and 752 nm peaks, which were a bit different from those under 975 nm excitation. Interestingly, we observed efficient energy transfer phenomena (possible quantum cutting) from Er3+/Ho3+ to Yb3+ and a Yb3+-O2- charge transfer (CT) transition in the molybdates, which was deduced from the visible and near-infrared emission spectra and the decrease of the Er3+/Ho3+ luminescent lifetimes with increasing Yb3+ concentration in the CsGd(MoO4)2:Yb3+,Er3+/Ho3+ samples. The luminescence properties of these phosphors suggest their potential possibility for applications in solid-state lighting and displays as well as in c-Si solar energy conversion systems.

Graphene Quantum Dots-Driven Multiform Morphologies of β-NaYF4:Gd3+/Tb3+ Phosphors: The Underlying Mechanism and Their Optical Properties

Dimension and shape tunable architectures of inorganic crystals are of extreme interest because of morphology-dependent modulation of the properties of the materials. Herein, for the first time, we present a novel impurity-driven strategy where we studied the influence of in situ incorporation of graphene quantum dots (GQDs) on the growth of β-NaYF₄:Gd³⁺/Tb³⁺ phosphor crystals via a hydrothermal route. The GQDs function as a nucleation site and by changing the concentration of GQDs, the morphology of β-NaYF₄:Gd³⁺/Tb³⁺ phosphors was changed from rod to flowerlike structure to disklike structure, without phase transformation. The influence of size and functionalization of GQDs on the size and shape of phosphor crystals were also systematically studied and discussed. Plausible mechanisms of formation of multiform morphologies are proposed based on the heterogeneous nucleation and growth. Most interestingly, the experimental results indicate that the photoluminescence properties of β-NaYF₄:Gd³⁺/Tb³⁺ phosphor crystals are strongly dependent on the crystallite size and morphology. This study would be suggestive for the precisely controlled growth of inorganic crystals; consequently, it will open new avenues and thus may possess potential applications in the field of materials and biological sciences.

Carbon Nano-Allotrope/Magnetic Nanoparticle Hybrid Nanomaterials as T2 Contrast Agents for Magnetic Resonance Imaging Applications

Magnetic resonance imaging (MRI) is the most powerful tool for deep penetration and high-quality 3D imaging of tissues with anatomical details. However, the sensitivity of the MRI technique is not as good as that of the radioactive or optical imaging methods. Carbon-based nanomaterials have attracted significant attention in biomaterial research in recent decades due to their unique physical properties, versatile functionalization chemistry, as well as excellent biological compatibility. Researchers have employed various carbon nano-allotropes to develop hybrid MRI contrast agents for improved sensitivity. This review summarizes the new research progresses in carbon-based hybrid MRI contrast agents, especially those reported in the past five years. The review will only focus on T2-weighted MRI agents and will be categorized by the different carbon allotrope types and magnetic components. Considering the strong trend in recent bio-nanotechnology research towards multifunctional diagnosis and therapy, carbon-based MRI contrast agents integrated with other imaging modalities or therapeutic functions are also covered.

Fluorescence turn-off Ag/fluorinated graphene composites with high NIR absorption for effective killing of cancer cells and bacteria

This study establishes FGO–Ag as a novel fluorescence “turn-off” nanocarrier with good targeting efficiency and high NIR absorption and drug loading; it also demonstrates its application in antibacterial and cancer chemo-photothermal treatments.

Investigation of photoluminescence properties, Judd–Ofelt analysis, luminescence nanothermometry and optical heating behaviour of Er3+/Eu3+/Yb3+:NaZnPO4 nanophosphors

The Er³⁺/Eu³⁺/Yb³⁺:NaZnPO₄ nanophosphors can be used as temperature sensors and optical nano-heaters with significant sensor sensitivity.

Luminescence and energy transfer in β-NaGdF4:Eu3+,Er3+ nanocrystalline samples from a room temperature synthesis

β-NaGdF₄:Eu³⁺,Er³⁺ nanoparticles were synthesized at room temperature. The synthesis is robust, easily scalable, and convenient. It is suitable for the whole lanthanide series.

Hydrothermal synthesis, down-/enhanced up-converting, color tuning luminescence, energy transfer and paramagnetic properties of Ln3+ (Ln = Eu/Dy, Yb/Ho)-doped Ba2GdF7 multifunctional nanophosphors

Tunable multicolor, energy transfer processes, and paramagnetic properties of the Ba₂GdF₇:Ln³⁺ (Ln = Eu/Dy, and Yb/Ho) nanophosphors were studied.

NaGdF4:Dy3+ nanofibers and nanobelts: facile construction technique, structure and bifunctionality of luminescence and enhanced paramagnetic performances

NaGdF₄:Dy³⁺ nanofibers and nanobelts with excellent luminescence-magnetic bi-functionality were fabricated via a combination of electrospinning and calcination with fluorination technology.

Multiwalled carbon nanotube hybrids as MRI contrast agents

Magnetic resonance imaging (MRI) is one of the most commonly used tomography techniques in medical diagnosis due to the non-invasive character, the high spatial resolution and the possibility of soft tissue imaging. Contrast agents, such as gadolinium complexes and superparamagnetic iron oxides, are administered to spotlight certain organs and their pathologies. Many new models have been proposed that reduce side effects and required doses of these already clinically approved contrast agents. These new candidates often possess additional functionalities, e.g., the possibility of bioactivation upon action of particular stimuli, thus serving as smart molecular probes, or the coupling with therapeutic agents and therefore combining both a diagnostic and therapeutic role. Nanomaterials have been found to be an excellent scaffold for contrast agents, among which carbon nanotubes offer vast possibilities. The morphology of multiwalled carbon nanotubes (MWCNTs), their magnetic and electronic properties, the possibility of different functionalization and the potential to penetrate cell membranes result in a unique and very attractive candidate for a new MRI contrast agent. In this review we describe the different issues connected with MWCNT hybrids designed for MRI contrast agents, i.e., their synthesis and magnetic and dispersion properties, as well as both in vitro and in vivo behavior, which is important for diagnostic purposes. An introduction to MRI contrast agent theory is elaborated here in order to point to the specific expectations regarding nanomaterials. Finally, we propose a promising, general model of MWCNTs as MRI contrast agent candidates based on the studies presented here and supported by appropriate theories.

Dual-mode, tunable color, enhanced upconversion luminescence and magnetism of multifunctional BaGdF5:Ln3+ (Ln = Yb/Er/Eu) nanophosphors

BaGdF₅:Yb³⁺,Er³⁺/Eu³⁺ nanophosphors were prepared by a hydrothermal method, and the energy transfer, color-tunable dual-mode emissions and magnetic properties were studied, which could have promising applications in the fields of LEDs, MRI, biolabels, and so on.

A new strategy to directly construct hybrid luminescence–photothermal–magnetism multifunctional nanocomposites for cancer up-conversion imaging and photothermal therapy

Novel hybrid Ag/NaGdF₄:Yb³⁺,Er³⁺ multifunctional nanocomposites with luminescence–photothermal–magnetism properties have great promise in future up-conversion luminescence imaging and photothermal therapy of tumors.