In situ passivation of Pb0 traps by fluoride acid-based ionic liquids enables enhanced emission and stability of CsPbBr3 nanocrystals for efficient white light-emitting diodes

A great hurdle restricting the optoelectronic applications of cesium lead halide perovskite (CsPbX₃) nanocrystals (NCs) is due to the uncoordinated lead atoms (Pb⁰) on the surface, where most attempts to address the challenges in the literature depend on complicated post-treatment processes. Here we report a simple in situ surface engineering strategy to obtain highly fluorescent and stable perovskite NCs, wherein the introduction of the multifunctional additive 1-butyl-3-methyl-imidazolium tetrafluoroborate ([Bmim]BF₄) can significantly eliminate the Pb⁰ traps. The photoluminescence quantum yield (PLQY) of the as-synthesized NCs was improved from 63.82% to 94.63% due to the good passivation of the surface defects. We also confirm the universality of this in situ passivation pathway to remove Pb⁰ deep traps by using fluoride acid-based ionic liquids (ILs). Due to the high hydrophobicity of the cations of ILs, the as-prepared CsPbBr₃ NCs exhibit robust water resistance stability, maintaining 67.5% of the initial photoluminescence (PL) intensity after immersion in water for 21 days. A white light emitting diode (LED), assembled by mixing the as-synthesized CsPbBr₃ NCs and red K₂SiF₆:Mn⁴⁺ phosphors onto a blue chip, exhibits high luminous efficiency (100.07 lm W^-1) and wide color gamut (140.64% of the National Television System Committee (NTSC) standard). This work provides a promising and facile technique to eliminate the Pb⁰ traps and improve the optical performance and stability of halide perovskite NCs, facilitating their applications in optoelectronic fields.

Facile synthesized NaGdF4 :Yb, Er peanut-shaped, highly biocompatible, colloidal upconversion nanospheres

A facile method was used for the synthesis of peanut-shaped very emissive NaGdF₄ :Yb, Er upconversion nanospheres (UCNSs) at lower temperatures with uniform size distribution. Crystallographic structure, phase purity, morphology, thermal robustness, biocompatibility, colloidal stability, surface chemistry, optical properties, and luminesce properties were explored by X-ray diffraction (XRD), Scanning electron microscope (SEM), transmission electron microscope (TEM), zeta potential, Thermogravimetric/thermal differential analysis (TGA/DTA), Fourier transform infrared (FTIR), UV/visible and photoluminescence spectroscopic tools. XRD pattern verified the construction of a single-phase, highly-crystalline NaGdF₄ phase with a hexagonal structure. Peanut-shaped morphology of the sample was obtained from SEM micrographs which were validated from high-resolution TEM images, have an equatorial diameter of 170-200 nm and a length of 220-230 nm, with irregular size, monodispersed, porous structure, and rough surface of the particles. The positive zeta potential value exhibited good biocompatibility along with high colloidal stability as observed from the absorption spectrum. The prepared UCNSs revealed high dispersibility, irregular size peanut-shaped morphology, rough surface, good colloidal stability, and excellent biocompatibility in aqueous media. A hexagonal phase NaGdF₄ doped with Yb, and Er UCNSs revealed the characteristics of highly dominant emissions located at 520-525, 538-550, and 659-668 nm are corresponding to the ² H_11/2 →⁴ I_15/2 , ⁴ S_3/2 →⁴ I_15/2 , and ⁴ F_9/2 →⁴ I_15/2 transition of Er³⁺ ions, respectively, as a result of energy transfer from sensitizer Yb³⁺ ion to emitter Er³⁺ ion.

Ionic Liquids and Deep Eutectics as a Transformative Platform for the Synthesis of Nanomaterials

Ionic liquids (ILs) are becoming a revolutionary synthesis medium for inorganic nanomaterials, permitting more efficient, safer and environmentally benign preparation of high quality products. A smart combination of ILs and...

Lanthanide-Doped Luminescent Nanophosphors via Ionic Liquids

Lanthanide (Ln3+) ion(s)-doped or rare-earth ion(s)-doped nanomaterials have been considered a very important class of nanophosphors for various photonic and biophotonic applications. Unlike semiconductors and organic-based luminescent particles, the optical properties of Ln3+-doped nanophosphors are independent of the size of the nanoparticles. However, by varying the crystal phase, morphology, and lattice strain of the host materials along with making core-shell structure, the relaxation dynamics of dopant Ln3+ ions can be effectively tuned. Interestingly, a judicious choice of dopant ions leads to unparallel photophysical dynamics, such as quantum cutting, upconversion, and energy transfer. Recently, ionic liquids (ILs) have drawn tremendous attention in the field of nanomaterials synthesis due to their unique properties like negligible vapor pressure, nonflammability, and, most importantly, tunability; thus, they are often called "green" and "designer" solvents. This review article provides a critical overview of the latest developments in the ILs-assisted synthesis of rare-earth-doped nanomaterials and their subsequent photonic/biophotonic applications, such as energy-efficient lighting and solar cell applications, photodynamic therapy, and in vivo and in vitro bioimaging. This article will emphasize how luminescence dynamics of dopant rare-earth ions can be tuned by changing the basic properties of the host materials like crystal phase, morphology, and lattice strain, which can be eventually tuned by various properties of ILs such as cation/anion combination, alkyl chain length, and viscosity. Last but not least, different aspects of ILs like their ability to act as templating agents, solvents, and reaction partners and sometimes their "three-in-one" use in nanomaterials synthesis are highlighted along with various photoluminescence mechanisms of Ln3+ ion like up- and downconversion (UC and DC).

Rare earth nanofluorides: synthesis using ionic liquids

This review presents a comprehensive summary of the research progress on the synthesis of rare earth fluoride nanomaterials using the most common methods of synthesis. Special focus is on syntheses utilising ionic liquids, which is a new and promising way of preparing nanomaterials without the use of dangerous organic solvents (toxic, flammable, or combustive). Rare earth fluoride nanoparticles can be obtained with a high yield, purity, and crystallinity, and with different morphologies and luminescent properties depending on the selected method of synthesis.

Ornamental morphology of ionic liquid functionalized ternary doped N, P, F and N, B, F-reduced graphene oxide and their prevention activities of bacterial biofilm-associated with orthopedic implantation

The multifunctional biological active material design for bone tissue engineering is essential to induce osteoblast cell proliferation and attachment. Adhesion of bacteria on biomaterials to produce biofilms can be major contributors to the pathogenesis of implant material associated infections. This research work focuses on NPF& NBF elemental doping and functionalization of reduced graphene oxide using an imidazolium-based ionic liquid such as BMIM PF₆ and BMIM BF₄ by hydrothermal method. The resulting tri doped reduced graphene oxide (NPF-rGO and NBF-rGO) composite was further used as a scaffold for bone tissue engineering and anti-biofilm activities. The observation of the effect of NPF-rGO and NBF-rGO on the morphology, adhesion and cell proliferation of HOS cell was investigated. Moreover, the tri doped composite tested its antibiofilm properties against B. subtilis, E. coli, K. pneumoniae, and P. aeruginosa pathogenic bacteria. In-vitro studies clearly show the effectiveness of N, P, B, and F doping promoting the rGO mineralization, biocompatibility, and destruction of bacterial biofilm formation. The result of this study suggests that NPF-rGO and NBF-rGO hybrid material will be a promising scaffold for bone reaeration and implantation with a minimal bacterial infection.

Trivalent rare-earth activated hexagonal lanthanum fluoride (LaF3 :RE3+ , where RE = Tb, Sm, Dy and Tm) nanocrystals: Synthesis and optical properties

The LaF₃ nanocrystals through a facile hydrothermal route with hexagonal structures have been synthesized via doping of trivalent rare earth (RE³⁺ ) ions - RE = Tb, Sm, Dy and Tm - with rod-like and perforated morphologies using NH₄ F as fluorine precursor. Hexagonal phase formation was confirmed by powder X-ray diffraction. The crystalline sizes were calculated by the Scherrer equation where found to have an average crystalline size of 12 to 35 nm. The morphological studies of the nanocrystals were carried out by means of transmission electron microscopy (TEM). The LaF₃ :Tm³⁺ ,Sm³⁺ ions show the characteristic emission of Tb³⁺ and Tm³⁺ respectively. In Sm³⁺ -doped LaF₃ , three prominent emission peaks at 561, 597 and 641 nm were found, which belong to ⁴ G_5/2  → ⁶ H_5/2 , ⁴ G_5/2  → ⁶ H_7/2 (magnetic dipole) and ⁴ G_5/2  → ⁶ H_9/2 (electric dipole) transitions, respectively. The Dy³⁺ activated LaF₃ shows blue and yellow emission and the corresponding CIE color coordinate show white light emission (CCT value 10650 K).

ZnWO4 nanocrystals: synthesis, morphology, photoluminescence and photocatalytic properties

The best photocatalytic properties for monoclinic ZnWO₄ nanocrystals are related to the surface energy and the types of clusters formed on their surface.

Visible transparent white light emitting ink from a Ce3+ sensitized monodispersed Tb,Sm co-doped LaF3@C-dot nanocomposite

A bright white light emitting WLED has been fabricated based on colloidal C-dots decorated with d-SiO₂ coated Ce, Tb and Sm doped LaF₃ nanoparticles.

Future prospects of luminescent nanomaterial based security inks: from synthesis to anti-counterfeiting applications

Counterfeiting of valuable documents, currency and branded products is a challenging problem that has serious economic, security and health ramifications for governments, businesses and consumers all over the world. It is estimated that counterfeiting represents a multi-billion dollar underground economy with counterfeit products being produced on a large scale every year. Counterfeiting is an increasingly high-tech crime and calls for high-tech solutions to prevent and deter the acts of counterfeiting. The present review briefly outlines and addresses the key challenges in this area, including the above mentioned concerns for anti-counterfeiting applications. This article describes a unique combination of all possible kinds of security ink formulations based on lanthanide doped luminescent nanomaterials, quantum dots (semiconductor and carbon based), metal organic frameworks as well as plasmonic nanomaterials for their possible use in anti-counterfeiting applications. Moreover, in this review, we have briefly discussed and described the historical background of luminescent nanomaterials, basic concepts and detailed synthesis methods along with their characterization. Furthermore, we have also discussed the methods adopted for the fabrication and design of luminescent security inks, various security printing techniques and their anti-counterfeiting applications.

Core–shell BaYbF5:Tm@BaGdF5:Yb,Tm nanocrystals for in vivo trimodal UCL/CT/MR imaging

PEGylated core–shell BaYbF₅:Tm@BaGdF₅:Yb,Tm nanocrystals have been constructed and successfully applied in UCL imaging, CT imaging and MR imaging.

Ionic liquids for nano- and microstructures preparation. Part 2: Application in synthesis

Ionic liquids (ILs) are widely applied to prepare metal nanoparticles and 3D semiconductor microparticles. Generally, they serve as a structuring agent or reaction medium (solvent), however it was also demonstrated that ILs can play a role of a co-solvent, metal precursor, reducing as well as surface modifying agent. The crucial role and possible types of interactions between ILs and growing particles have been presented in the Part 1 of this review paper. Part 2 of the paper gives a comprehensive overview of recent experimental studies dealing with application of ionic liquids for preparation of metal and semiconductor based nano- and microparticles. A wide spectrum of preparation routes using ionic liquids is presented, including precipitation, sol-gel technique, hydrothermal method, nanocasting and ray-mediated methods (microwave, ultrasound, UV-radiation and γ-radiation). It was found that ionic liquids formed of a 1-butyl-3-methylimidazolium [BMIM] combined with tetrafluoroborate [BF4], hexafluorophosphate [PF6], and bis(trifluoromethanesulfonyl)imide [Tf2N] are the most often used ILs in the synthesis of nano- and microparticles, due to their low melting temperature, low viscosity and good transportation properties. Nevertheless, examples of other IL classes with intrinsic nanoparticles stabilizing abilities such as phosphonium and ammonium derivatives are also presented. Experimental data revealed that structure of ILs (both anion and cation type) affects the size and shape of formed metal particles, and in some cases may even determine possibility of particles formation. The nature of the metal precursor determines its affinity to polar or nonpolar domains of ionic liquid, and therefore, the size of the nanoparticles depends on the size of these regions. Ability of ionic liquids to form varied extended interactions with particle precursor as well as other compounds presented in the reaction media (water, organic solvents etc.) provides nano- and microstructures with different morphologies (0D nanoparticles, 1D nanowires, rods, 2D layers, sheets, and 3D features of molecules). ILs interact efficiently with microwave irradiation, thus even small amount of IL can be employed to increase the dielectric constant of nonpolar solvents used in the synthesis. Thus, combining the advantages of ionic liquids and ray-mediated methods resulted in the development of new ionic liquid-assisted synthesis routes. One of the recently proposed approaches of semiconductor particles preparation is based on the adsorption of semiconductor precursor molecules at the surface of micelles built of ionic liquid molecules playing a role of a soft template for growing microparticles.

Synthesis, characterization, and cytotoxicity in human erythrocytes of multifunctional, magnetic, and luminescent nanocrystalline rare earth fluorides

Multifunctional nanoparticles exhibiting red or green luminescence properties and magnetism were synthesized and thoroughly analyzed. The hydrothermal method was used for the synthesis of Eu3+- or Tb3+-doped GdF3-, NaGdF4-, and BaGdF5-based nanocrystalline materials. The X-ray diffraction patterns of the samples confirmed the desired compositions of the materials. Transmission electron microscope images revealed the different morphologies of the products, including the nanocrystal sizes, which varied from 12 nm in the case of BaGdF5-based nanoparticles to larger structures with dimensions exceeding 300 nm. All of the samples presented luminescence under ultraviolet irradiation, as well as when the samples were in the form of water colloids. The highest luminescence was observed for BaGdF5-based materials. The obtained nanoparticles exhibited paramagnetism along with probable evidence of superparamagnetic behavior at low temperatures. The particles' magnetic characteristics were also preserved for samples in the form of a suspension in distilled water. The cytotoxicity studies against the human erythrocytes indicated that the synthesized nanoparticles are non-toxic because they did not cause the red blood cells shape changes nor did they alter their membrane structure and permeabilization.

β-NaGdF4 nanotubes: one-pot synthesis and luminescence properties

Hexagonal-phase NaGdF4 nanotubes were successfully fabricated through a template- and catalyst-free method in a hydrothermal environment. The intrinsic and external factors contributing to the formation of tubular nanocrystals were discussed, namely the anisotropic crystal structure of the hexagonal-phase NaGdF4 and the insufficient supply of reagents. Furthermore, the addition of ethylene glycol and hydrazine had a significant effect on the morphological variation. The desirable multicolor outputs were achieved by co-doping Ce(3+) and Ln(3+) (Ln = Eu, Tb, and Dy) ions in the NaGdF4 crystal, in which the Gd(3+) ions acted as an intermediate medium transforming the excitation energy to the activator ions. Finally, the upconversion luminescence and magnetic performance of the sodium rare earth fluoride were demonstrated.

One-pot, template-free synthesis of hydrophobic single-crystalline La(OH)3 nanowires with tunable size and their d0 ferromagnetic properties

Hydrophobic single-crystalline La(OH)₃ nanowires with tunable size have been fabricated by a facile one-pot liquid–solid-solution (LSS) assisted hydrothermal method without any template and their morphology, chemistry and crystal structure were characterized at nanoscale.

Investigation on YF3:Eu3+ architectures and their luminescence properties

The changeable matrix under different calcination temperatures leads to tunable luminescence properties.

Synthesis, optical properties, and energy transfer of Ce(3+)/Tb(3+) co-doped MyGdFx (M=Li, Na, K)

Through a solid-state reaction method, the Ce(3+)/Tb(3+) co-doped MyGdFx (M=Li, Na, K; x=3, 4, 6; y=0, 1, 3) system samples have been synthesized by controlling the annealing temperatures and the ratios of raw materials. The samples were characterized by X-ray diffraction (XRD) patterns, photoluminescence (PL) excitation and emission spectra as well as luminescent dynamic decay curves. The experimental results suggest that the LiF is more difficult to react with the prepared material compared that of NaF or KF under similar reaction conditions. The samples crystallized in different crystalline phases. The energy transfer from Ce(3+) to Tb(3+) or Ce(3+) to Gd(3+) to Tb(3+) has been observed in all the samples. The Ce(3+) and Tb(3+) present different optical properties for they are sensitive to the local environment. In addition, the deduced lifetime of Tb(3+)(5)D4→(7)F5 transition decreases in the same system samples with the annealing temperature increasing. The deduced lifetime of Tb(3+)(5)D4→(7)F5 also decreases with the increase of the KF concentration in the KF system samples.

Room temperature synthesis of hydrophilic Ln(3+)-doped KGdF4 (Ln = Ce, Eu, Tb, Dy) nanoparticles with controllable size: energy transfer, size-dependent and color-tunable luminescence properties

In this paper, we demonstrate a simple, template-free, reproducible and one-step synthesis of hydrophilic KGdF(4): Ln(3+) (Ln = Ce, Eu, Tb and Dy) nanoparticles (NPs) via a solution-based route at room temperature. X-Ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), photoluminescence (PL) and cathodoluminescence (CL) spectra are used to characterize the samples. The results indicate that the use of water-diethyleneglycol (DEG) solvent mixture as the reaction medium not only allows facile particle size control but also endows the as-prepared samples with good water-solubility. In particular, the mean size of NPs is monotonously reduced with the increase of DEG content, from 215 to 40 nm. The luminescence intensity and absolute quantum yields for KGdF(4): Ce(3+), Tb(3+) NPs increase remarkably with particle sizes ranging from 40 to 215 nm. Additionally, we systematically investigate the magnetic and luminescence properties of KGdF(4): Ln(3+) (Ln = Ce, Eu, Tb and Dy) NPs. They display paramagnetic and superparamagnetic properties with mass magnetic susceptibility values of 1.03 × 10(-4) emu g(-1)·Oe and 3.09 × 10(-3) emu g(-1)·Oe at 300 K and 2 K, respectively, and multicolor emissions due to the energy transfer (ET) process Ce(3+)→ Gd(3+)→ (Gd(3+))(n)→ Ln(3+), in which Gd(3+) ions play an intermediate role in this process. Representatively, it is shown that the energy transfer from Ce(3+) to Tb(3+) occurs mainly via the dipole-quadrupole interaction by comparison of the theoretical calculation and experimental results. This kind of magnetic/luminescent dual-function materials may have promising applications in multiple biolabels and MR imaging.