Strategy to Enhance the Luminescence of Lanthanide Ions Doped MgWO4 Nanosheets through Incorporation of Carbon Dots

Dual-mode luminescence anti-counterfeiting and white light emission of NaGdF4:Ce,Eu,Tb/carbon dot hydrophilic nanocomposite ink

NaGdF4:Ce,Eu,Tb nanocrystals were successfully prepared by a one-step hydrothermal method with Ce3+ ions as sensitizers, Eu3+ and Tb3+ ions as activators, and polyethylenimine (PEI) as surfactants. Color-adjustable fluorescence emission was achieved by the energy transfer effect between rare earth ions. Blue fluorescent carbon quantum dots (CDs) with a double UV response under 254 nm and 365 nm excitation were synthesized by a one-step hydrothermal method. A hydrophilic NaGdF4:Ce,Eu,Tb/CD composite ink was prepared by an easy physical mixing method. Because of the electrostatic self-assembly effect, the color adjustable luminescence was achieved in a few seconds, and the white light emission with color coordinates of (0.32, 0.32) was obtained. A dual-mode luminescence anti-counterfeiting pattern was designed and achieved by excitation with ultraviolet light at 254 nm and 365 nm.

Combined structural analysis and cathodoluminescence investigations of single Pr3+-doped Ca2Nb3O10 nanosheets

Due to the novel properties of both 2D materials and rare-earth elements, developing 2D rare-earth nanomaterials has a growing interest in research. To produce the most efficient rare-earth nanosheets, it is essential to find out the correlation between chemical composition, atomic structure and luminescent properties of individual sheets. In this study, 2D nanosheets exfoliated from Pr³⁺-doped KCa₂Nb₃O₁₀ particles with different Pr concentrations were investigated. Energy dispersive X-ray spectroscopy analysis indicates that the nanosheets contain Ca, Nb and O and a varying Pr content between 0.9 and 1.8 at%. K was completely removed after exfoliation. The crystal structure is monoclinic as in the bulk. The thinnest nanosheets are 3 nm corresponding to one triple perovskite-type layer with Nb on the B sites and Ca on the A sites, surrounded by charge compensating TBA⁺ molecules. Thicker nanosheets of 12 nm thickness (and above) were observed too by transmission electron microscopy with the same chemical composition. This indicates that several perovskite-type triple layers remain stacked similar to the bulk. Luminescent properties of individual 2D nanosheets were studied using a cathodoluminescence spectrometer revealing additional transitions in the visible region in comparison to the spectra of different bulk phases.

Investigation of the photoluminescent properties, scintillation behaviour and toxicological profile of various magnesium tungstate nanoscale motifs

We have synthesized several morphologies and crystal structures of MgWO₄ using a one-pot hydrothermal method, producing not only monoclinic stars and large nanoparticles but also triclinic wool balls and sub-10 nm nanoparticles. Herein we describe the importance of reaction parameters in demonstrating morphology control of as-prepared MgWO₄. Moreover, we correlate structure and composition with the resulting photoluminescence and radioluminescence properties. Specifically, triclinic-phase samples yielded a photoluminescence emission of 421 nm, whereas monoclinic-phase materials gave rise to an emission maximum of 515 nm. The corresponding radioluminescence data were characterized by a broad emission peak, located at 500 nm for all samples. Annealing the wool balls and sub-10 nm particles to transform the crystal structure from a triclinic to a monoclinic phase yielded a radioluminescence (RL) emission signal that was two orders of magnitude greater than that of their unannealed counterparts. Finally, to confirm the practical utility of these materials for biomedical applications, a series of sub-10 nm particles, including as-prepared and annealed samples, were functionalized with biocompatible PEG molecules, and subsequently were found to be readily taken up by various cell lines as well as primary cultured hippocampal neurons with low levels of toxicity, thereby highlighting for the first time the potential of this particular class of metal oxides as viable and readily generated platforms for a range of biomedical applications.

Simultaneous effects of synthesis temperature and dopants on MgWO4UC phosphors

A sequence of coactivated divalent-metal tungstate Er3+/Yb3+/Mn4+: MgWO4 phosphors have been successfully developed to study the effect of synthesis temperature on the crystal structure, surface morphology, fluorescence, temperature sensing and the dynamics involved in the processes. Upconversion (UC) intensity of the Er3+/Yb3+: MgWO4 phosphors increased by ~ 109 and ~ 778 times on increasing the synthesis temperature from 800 ºC to 1000 ºC and 1200 ºC. UC intensity of the Er3+/Yb3+/Mn4+: MgWO4 phosphors has been significantly improved up to ~ 90 times via charge compensation. The incorporation of Mn4+ in the Er3+/Yb3+ codoped crystal system shifted the UC spectra from sharp green peaks to broadband emission along with amended sensing abilities. The ratiometric techniques of thermally coupled stark sublevels of the Er3+ have been used to achieve a wide temperature range (300 - 623K). The prepared nanophosphors show maximum absolute & relative sensitivities ~ 25.86×10-3 K-1 @453K and ~ 10.39×10-3 K-1 @303 K respectively with an accuracy of ± 0.42K@303K.

An enhanced fluorescent probe through the strategy of using MgWO4 nanosheets to enhance terbium ion luminescence for highly sensitive and point-of-care visual quantitative testing of ciprofloxacin integrated with a low-cost smartphone-based platform

In this work, MgWO₄ nanosheets have been successfully synthesized by a simple hydrothermal method, and the morphology and composition of the MgWO₄ nanosheets are characterized by SEM, TEM, XPS, and UV-vis. The results show that the as-prepared MgWO₄ nanosheets have a triclinic symmetry phase and an obvious two-dimensional layered structure. Studies have shown that the MgWO₄ semiconductor nanosheets can adjust the energy level, which significantly enhances the visible light absorption and the separation and transfer of photogenerated electrons, which facilitates the generation of photogenerated electrons. We use this feature to boost a terbium ion (Tb³⁺)-ciprofloxacin (CIP) system to enhance the luminescence, so as to achieve highly sensitive detection of CIP. The mechanism of Tb³⁺-MgWO₄ for CIP detection is the effective energy transfer from WO₄^2- in MgWO₄ nanosheets to Tb³⁺-CIP, thereby enhancing the characteristic emission of Tb³⁺ and enhancing the sensitivity of CIP detection. The linear response of the Tb³⁺-MgWO₄ enhanced fluorescent probe is in the range from 10 nM to 20 μM, and the detection limit (LOD) is 2 nM. In addition, we tested the recovery in spiked river water and mouse serum. Experiments have shown that the recovery of spiked samples is 97-102.2%, while the relative standard deviation (RSD) is less than 5.53%. The possible interfering substances in environmental samples will not interfere with the detection of CIP with the Tb³⁺-MgWO₄ enhanced fluorescent probe. At the same time, the development of a smartphone-based portable device provides the possibility of CIP on-site detection. Our work provides a simple, fast, highly sensitive and stable method for detecting CIP in living organisms and the environment. Importantly, the strategy of MgWO₄ nanosheet boosted terbium ion luminescence expands the application range of semiconductor nanomaterials.

A strategy to enhance the up-conversion luminescence of nanospherical, rod-like and tube-like NaYF4: Yb3+, Er3+ (Tm3+) by combining with carbon dots

The luminescence enhanced strategy of combining the material with carbon dots to form CDs@NaYF₄: Yb³⁺, Er³⁺ (Tm³⁺) composites is effective not only for the cubic- and hexagonal-phase materials but also for those with different morphologies.

When rare earth meets carbon nanodots: mechanisms, applications and outlook

Rare earth (RE) elements are widely used in the luminescence and magnetic fields by virtue of their abundant 4f electron configurations. However, the overall performance and aqueous stability of single-component RE materials need to be urgently improved to satisfy the requirements for multifunctional applications. Carbon nanodots (CNDs) are excellent nanocarriers with abundant functional surface groups, excellent hydrophilicity, unique photoluminescence (PL) and tunable features. Accordingly, RE-CND hybrids combine the merits of both RE and CNDs, which dramatically enhance their overall properties such as luminescent and magnetic-optical imaging performances, leading to highly promising practical applications in the future. Nevertheless, a comprehensive review focusing on the introduction and in-depth understanding of RE-CND hybrid materials has not been reported to date. This review endeavors to summarize the recent advances of RE-CNDs, including their interaction mechanisms, general synthetic strategies and applications in fluorescence, biosensing and multi-modal biomedical imaging. Finally, we present the current challenges and the possible application perspectives of newly developed RE-CND materials. We hope this review will inspire new design ideas and valuable references in this promising field in the future.

Synergetic Effect of Tetraethylammonium Bromide Addition on the Morphology Evolution and Enhanced Photoluminescence of Rare-Earth Metal-Organic Frameworks

Controlled synthesis of rare-earth metal-organic frameworks (RE-MOFs) is of great significance to match their emerging multifunctional luminescence applications. Herein, we propose a green and general solvent-free synthetic strategy for the adjustment of morphology and dimension of various RE-MOFs (RE = Eu, Tb, Er, Dy, Y, Tm) by using a tetraethylammonium bromide-assisted thermal-heating method. These self-assembled RE-MOF materials possess controllable morphologies and hierarchical structures while retaining the structural topology of MIL-78, proving that the strategy is a feasible and effective way in opening up large-scale synthesis of RE-MOFs. It is further found that the tetraethylammonium could be carbonized into carbon dots and encapsulated in Eu/Tb-MIL-78 to enhance the fluorescence emission intensities significantly, making the hierarchical Eu/Tb-MIL-78 MOF materials good candidates for the latent fingerprints recognition application. This work provides a novel strategy for effectively controlling the morphology and dimension of RE-MOFs materials with enhanced photoluminescence and has great potential in their scaling-up syntheses and exploring the new luminescence applications.

Luminescence properties and energy transfer of Tb3+, Eu3+ co-doped YTaO4 phosphors obtained via sol-gel combustion process

Tantalate is considered as a valuable and efficient luminescence host because of its intense absorption in the ultraviolet area and excellent chemical properties. In this work, a series of pure YTaO4:Eu3+ and/or Tb3+ crystals were prepared via a sol-gel combustion method. The morphology, structure, and optical properties of the samples were discussed in detail. The Eu3+, Tb3+ co-doped YTaO4 samples are consisted of small spherical particles of around 18 nm. The prepared YTaO4:Tb3+ and/or Eu3+ samples exhibit the characteristic wide excitation band around 210-300 nm, the characteristic narrow red emission of Eu3+ (5D0 → 7F2) transitions and green emission of the Tb3+ (5D4 → 7F5) transitions when excited by UV light. It is focused on the energy transfer processes from the YTaO4 to Tb3+ as well as Eu3+ ions and from Tb3+ to Eu3+ ions of YTaO4:Eu3+/Tb3+ phosphors. Color-tunable emissions are realized through adjusting the types of rare earth ion (Eu3+ and Tb3+) and relative doping concentrations excited by a single wavelength. That is to say, the obtained Tb3+ and Eu3+ co-doped YTaO4 phosphors have a promising prospect in lasers, white light diodes (WLED), fluorescent lamp, and field emission display devices, etc.

An insight into the molecular structures, theoretical calculation and catalytic activities of novel heterotrinuclear [CuII2CeIII] and heterohexanuclear [CuII4YIII2] bis(salamo)-based complexes

Two heteropolynuclear complexes, [Cu^II₂Ce^III] [Cu₂(L)Ce(NO₃)₃] and [{Cu₂(L)Y(NO₃)₂(μ-AcO)}{Cu₂(L)Y(NO₃)₂(μ-NO₃)(CH₃OH)}]·4CH₃OH, were synthesized. It was found that only the [Cu^II₂Ce^III] complex showed high catecholase and benzoxazinone synthase like catalytic activity.

A convenient and universal platform for sensing environmental nitro-aromatic explosives based on amphiphilic carbon dots

2,4,6-trinitrophenol (TNP) is environmentally deleterious substance that has been of pressing societal concern. Therefore, developing a convenient and reliable platforms for its fast and efficient detection is of paramount importance from security point of view. Herein, amphiphilic fluorescent carbon dots (CDs) were prepared by a simple solvothermal method. CDs exhibit high selectivity and sensitivity on TNP in the polar and apolar solvent and even natural water samples. Moreover, the simple and portable indicator paper can be prepared conveniently and used for sensing TNP visually with high sensitivity and fast response. Research findings obtained from this study would assist in the development of portable devices for the on-site and real-time detection of environmental hazards.

Controllable synthesis of multi-morphological SrWO4:Ln3+ (Ln = Eu, Tb) hierarchical structures and their luminescence properties

Multi-morphological SrWO₄:Ln³⁺ hierarchical structures including dumbbell-like, nanosheets, rice-like, peanut-like, etc. could be controllably synthesized through readily altering reaction conditions.

Facile synthesis, morphology and tunable photoluminescence properties of BaMgF4:Ce3+/Tb3+/Eu3+ phosphors

A series of BaMgF₄:Ce³⁺/Tb³⁺/Eu³⁺ phosphors were successfully prepared via a facile hydrothermal process.