Microcrystalline Luminescent (Eu1-xLnx)2bdc3·nH2O (Ln = La, Gd, Lu) Antenna MOFs: Effect of Dopant Content on Structure, Particle Morphology, and Luminescent Properties

In this work, three series of micro-sized heterometallic europium-containing terephthalate MOFs, (Eu1-xLnx)2bdc3·nH2O (Ln = La, Gd, Lu), are synthesized via an ultrasound-assisted method in an aqueous medium. La3+ and Gd3+-doped terephthalates are isostructural to Eu2bdc3·4H2O. Lu3+-doped compounds are isostructural to Eu2bdc3·4H2O with Lu contents lower than 95 at.%. The compounds that are isostructural to Lu2bdc3·2.5H2O are formed at higher Lu3+ concentrations for the (Eu1-xLux)2bdc3·nH2O series. All materials consist of micrometer-sized particles. The particle shape is determined by the crystalline phase. All the synthesized samples demonstrate an "antenna" effect: a bright-red emission corresponding to the 5D0-7FJ transitions of Eu3+ ions is observed upon 310 nm excitation into the singlet electronic excited state of terephthalate ions. The fine structure of the emission spectra is determined by the crystalline phase due to the different local symmetries of the Eu3+ ions in the different kinds of crystalline structures. The photoluminescence quantum yield and 5D0 excited state lifetime of Eu3+ are equal to 11 ± 2% and 0.44 ± 0.01 ms, respectively, for the Ln2bdc3·4H2O structures. For the (Eu1-xLux)2bdc3·2.5H2O compounds, significant increases in the photoluminescence quantum yield and 5D0 excited state lifetime of Eu3+ are observed, reaching 23% and 1.62 ms, respectively.

Exploring the effect of boron on the grain morphology change and spectral properties of Eu3+ activated barium tantalate phosphor

The effect of the grain morphology on the photoluminescence, charge transfer band, and decay properties was investigated by xEu3+, yB3+ (x = 10 mol%, y = 0, 5, 15, 30, 50, 70, and 100 mol%) co-doped BaTa2O6 ceramics fabricated by solid-state reaction. X-ray diffractions of the samples showed that the single-phase structure persisted up to 100 mol% and there was an improvement in crystallinity with increasing B3+ concentration. SEM micrographs of the Eu3+, B3+ co-doped grains showed that the flux effect of boron promotes grain growth and elongated grain shape. The PL emissions of the BaTa2O6:xEu3+, yB3+ co-doped phosphors increased up to 100 mol% B3+ concentration, and there was an increase in the intensities of the CTB energy 5D0 → 7F1 transition. The increase in PL may be attributed to the increased grain size leading to a decrease in the surface area (SA)/volume (vol) ratio with increasing B3+ concentration, as well as the improvement in crystallinity. However, the decrease in asymmetry ratio was related to the occupation of centrosymmetric (B) sites and the transformation from a rounded/irregular-like to an elongated/rod-like grain shape which has an increasing effect on the SA/vol ratio. The decreasing trend of the Judd-Ofelt parameters (Ω2, and Ω4) with the increase in boron was related to a high local symmetry of Eu3+ sites, and an increase in the electron density of the surrounding ligands, respectively. The increase in boron led to longer decays in the observed lifetime with bi-exponential characteristics. The CIE diagram and UV lamp photographs of the phosphors showed a color transition from red to orange associated with the increasing magnetic dipole transition. This study may provide an alternative perspective and new strategies to describe the control of grain morphology and luminescence concerning RE-doped phosphors.

Boron doping effect on the structural, spectral properties and charge transfer mechanism of orthorhombic tungsten bronze β-SrTa2O6:Eu3+ phosphor

In the study, the effect of boron doping on spectral properties and CTB mechanism was investigated by using Eu³⁺ doped orthorhombic β-SrTa₂O₆. A phosphor series of Eu³⁺ doped SrTa₂O₆, and Eu³⁺ and B³⁺ co-doped SrTa₂O₆ polycrystals were fabricated by solid-state reaction at 1400 °C for 20 h in an air atmosphere. The X-ray diffractions of the main phase structure for all the ceramics maintained up to 10 mol% Eu³⁺ concentration, while the increase of XRD intensity for Eu³⁺ and B³⁺ co-doped samples was attributed to somewhat improvement of crystallization. SEM morphologies of grains showed that the presence of boron promotes agglomeration and grain growth. The doping of boron up to 20 mol% led to an increase in PL intensity, CTB energy slightly shifted to low energy, and also an increase occurred in the asymmetry ratio of the phosphor. Therefore, the low crystal field symmetry of the Eu³⁺ sites and some improvement in crystal structure properties for Eu³⁺, B³⁺ co-doped samples supported the PL increase. The trend of Judd-Ofelt parameters (Ω ₂, Ω ₄) is SrTa₂O₆:xEu³⁺, 0.1B³⁺ > SrTa₂O₆:xEu³⁺. The high Ω ₂ parameter for boron co-doped samples showed a covalent Eu-O bond character with low symmetry of Eu³⁺ environment, while the high Ω ₄ value indicated the reduction in electron density of the ligands. Some increase in the short decays of Eu³⁺, B³⁺ co-doped samples is probably due to the surface effect and low crystal field symmetry. The quantum efficiency of 0.05Eu³⁺, 0.1B³⁺ co-doped phosphor with the highest PL intensity increased by about 21% compared to that without boron.

Room-temperature and ultrafast Eu3+ ion doping for highly luminescent and extremely small CaMoO4 nanocrystals

We developed a room-temperature and ultrafast Eu³⁺-ion doping approach for the synthesis of highly luminescent Eu-doped CaMoO₄ nanoparticles. Firstly, CaMoO₄ nanoparticles with a particle size of 3.9 nm are rapidly prepared using a room temperature co-precipitation approach. Subsequently, Eu-doped CaMoO₄ nanoparticles with a photoluminescence quantum yield of up to 75% are synthesized by a post-cation exchange reaction at room temperature. This facile and room-temperature synthetic strategy enables us to prepare highly luminescent and extremely small rare earth ion-doped metal oxide nanocrystals.

Investigation of thermoluminescence and photoluminescence properties of Tb3+, Eu3+, and Dy3+ doped NaYF4 phosphors for dosimetric applications

Hexagonal phase sodium yttrium fluoride activated with lanthanide ions; Tb³⁺, Eu³⁺ and Dy³⁺ doped NaYF₄ phosphors were synthesized using a simplistic hydrothermal method. The photoluminescence studies demonstrated green, red and blue emission lines corresponding to ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3), ⁵D₀ → ⁷F_J (J = 1, 2 and 4) and ⁴F_9/2 to ⁶H_J (J = 15/2 and 13/2) transitions, which are characteristic of Tb³⁺, Eu³⁺ and Dy³⁺ ions, respectively. The as-synthesized samples were subjected to annealing at varying temperatures from 500 °C to 800 °C primarily for the optimization of the thermoluminescence glow curve. Meanwhile, we studied the influence of thermal annealing treatment on the crystal phase, morphological features, and photoluminescence properties of the phosphors. The spherical-like morphology of NaYF₄:Tb³⁺ phosphor changed to micro block-like structures and the hexagonal phase of NaYF₄ transforms into a cubic phase at a higher annealing temperature of ∼800 °C. The photoluminescence emission intensity also varied at different annealing temperatures. The systematic study using different dopants and annealing temperatures was carried out to accomplish efficient thermoluminescence (TL) properties. The most suitable TL dosimetric glow peak was attained for NaYF₄:0.5%Tb³⁺ phosphor, which was annealed at a temperature of 800 °C, located at 194 °C. The NaYF₄:Tb³⁺ phosphor exhibited TL response fairly linear in the dose range from 1 kGy to 25 kGy of gamma radiation. The phosphor showed TL response at higher doses, which stipulates that the NaYF₄:Tb³⁺ is reasonably well suitable for high dose measurements and respective applications. The phosphor exhibited negligible fading and good reproducibility features. Trap-level analysis and experimental determination of activation energy were performed using the T_m-T_stop technique and initial rise method (IRM). The trapping parameters of the TL glow curve, such as activation energy (E), order of kinetics (b), and frequency factor (s) were estimated by Chen's glow peak shape (PS) method and glow curve deconvolution (GCD) method. The trapping parameters obtained using the IRM, PS and GCD methods are in good accordance with each other. Henceforth, along with efficient photoluminescence properties, the NaYF₄:Tb³⁺ phosphor exhibited favorable thermoluminescence dosimetric properties. Consequently, this study provides new opportunities for utilizing these phosphors in the area of radiation dosimetry applications such as environmental and food monitoring, space dosimetry etc.

Eu3+ Doped LaF3 -based Inorganic-organic Hybrid Nanostructured Materials for Broad-spectrum Excitation and Strong Photoluminescence

Inorganic-organic hybrid nanoparticles formed by lanthanide-doped nanostructures and organic ligands have been intensively studied, which could greatly increase their photoluminescence performance as a result of the energy transfer process from organic ligands to Ln³⁺ ions. However, the photoluminescence intensity and excitation spectral width are still quite limited on coordinating with a single type of organic ligand. In this work, Eu³⁺ -doped LaF₃ (LaF₃ :Eu³⁺ ) nanoparticles were prepared using hydrothermal method, which was then hybridized with benzoic acid and thenoyltrifluoroacetone to form the hybrid nanostructures. After that, the hybrid nanostructures were mixed with 2,2'-azobisisobutyronitrile and methyl methacrylate to prepare the composites. The sample obtained by hybridization and composite doping with 5% Eu³⁺ exhibited the best photoluminescence performance. The excitation peak width and luminescence intensity of the hybrid nanostructures were significantly increased. The excitation spectral width of the inorganic-organic mixed hybrid nanostructures was particularly enhanced, which covers the whole ultraviolet (UV) band region of solar light on earth. The prepared composites exhibited good optical properties.

Multireference Ab Initio Investigation on Ground and Low-Lying Excited States: Systematic Evaluation of J-J Mixing in a Eu3+ Luminescent Complex

A theoretical protocol combining density functional theory (DFT) and multireference (CAS) calculations is proposed for a Eu³⁺ complex. In the complex, electronic levels of the central Eu³⁺ ion are correctly calculated at the CASPT2 level of theory, and the effect of introducing different numbers of states in the configuration interaction matrices is highlighted as well as the shortcomings of DFT methods in the treatment of systems with high spin multiplicity and strong spin–orbit coupling effects. For the ⁵D₀ state energy calculation, the inclusion of states with different multiplicity and the number of states considered for each multiplicity are crucial parameters, even if their relative weight is different. Indeed, the addition of triplet and singlets is important, while the number of states is relevant only for the quintets. The herein proposed protocol enables a rigorous, full ab initio treatment of Eu³⁺ complex, which can be easily extended to other Ln³⁺ ions.

A theoretical protocol combining density functional theory and multireference calculations is proposed for a Eu³⁺ complex. For the ⁵D₀ state energy calculation, the inclusion of states with different multiplicity and the number of states considered for each multiplicity are crucial parameters. The herein proposed protocol enables a rigorous, full ab initio treatment of Eu³⁺ complex, which can be easily extended to other Ln³⁺ ions.

The effect of Eu3+ and Gd3+ co-doping on the morphology and luminescence of NaYF4:Eu3+, Gd3+ phosphors

Eu³⁺ and Gd³⁺ doping results in the size reduction of β-NaYF₄: Eu³⁺, Gd³⁺ microparticles; Gd³⁺ co-doping enhances the luminescence intensity.

A Comparative Study on Luminescence Properties of Y2O3: Pr3+ Nanocrystals Prepared by Different Synthesis Methods

Pr³⁺-doped Y₂O₃ nanocrystals (NCs) have been obtained via five wet-chemistry synthesis methods which were optimized in order to achieve superior optical properties. To this end, a systematic study on the influence of different reaction parameters was performed for each procedure. Specifically, precursor concentration, reaction temperature, calcination temperature, and time, among others, were analyzed. The synthesized Y₂O₃: Pr³⁺ NCs were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), and reflectance and Raman spectroscopy. In addition, the optical properties of such NCs were investigated by excitation, emission, and luminescence decay measurements. Concretely, emission from the ¹D₂ level was detected in all samples, while emission from ³P_J was absent. Finally, the effect of the synthesis methods and the reaction conditions on the luminescence decay has been discussed, and a comparative study of the different methods using the fluorescence lifetime of so-obtained Y₂O₃: Pr³⁺ NCs as a figure of merit has been carried out.

Phase Control in Hafnia: New Synthesis Approach and Convergence of Average and Local Structure Properties

Technologically relevant tetragonal/cubic phases of HfO₂ can be stabilized at room temperature by doping with trivalent rare earths using various approaches denoted generically as bulk coprecipitation. Using in situ/ex situ X-ray diffraction (XRD), Raman spectroscopy, high-resolution transmission electron microscopy, and in situ/ex situ site-selective, time-gated luminescence spectroscopy, we show that wet impregnation of hafnia nanoparticles with 10% Eu oxide followed by mild calcination in air at 500 °C produces an efficient stabilization of the cubic phase, comparable to that obtained by bulk precipitation. The physical reasons behind the apparently conflictual data concerning the actual crystallographic phase and the local symmetry around the Eu stabilizer and how these can be mediated by luminescence analysis are also discussed. Apparently, the cubic crystal structure symmetry determined by XRD results in a pseudocubic/tetragonal local structure around Eu determined by luminescence. Considering the recent findings on wet impregnated CeO₂ and ZrO₂, it is concluded that CeO₂, ZrO₂, and HfO₂ represent a unique case of a family of oxides that is extremely tolerant to heavy doping by wet impregnation. In this way, the same batch of preformed nanoparticles can be doped with different lanthanide concentrations or with various lanthanides at a fixed concentration, allowing a systematic and reliable investigation of the effect of doping, lanthanide type, and lanthanide concentration on the various functionalities of these technologically relevant oxides.

Structural, luminescence and thermometric properties of nanocrystalline YVO4:Dy3+ temperature and concentration series

We report systematic study of Dy³⁺-doped YVO₄ nanophosphors synthesized via modified Pechini technique. Effect of calcination temperature and doping concentration on structure and luminescence has been investigated. XRD and Raman spectroscopy revealed preparation of single phase nanoparticles without any impurities. Synthesized nanopowders consisted of weakly agglomerated nanoparticles with average size about 50 nm. Photoluminescence spectra of YVO₄:Dy³⁺ nanoparticles consisted of the characteristic narrow lines attributed to the intra-configurational 4f-4f transitions dominating by the hypersensitive ⁴F_9/2–⁶H_13/2 transition. The calcination temperature variation did not affect ⁴F_9/2 lifetime, whereas increase of doping concentration resulted in its gradual decline. Potential application of YVO₄:Dy³⁺ 1 at.% and 2 at.% nanopowders as ratiometric luminescence thermometers within 298–673 K temperature range was tested. The main performances of thermometer including absolute and relative thermal sensitivities and temperature uncertainty were calculated. The maximum relative thermal sensitivity was determined to be 1.8% K⁻¹@298 K, whereas the minimum temperature uncertainty was 2 K.

Charge compensation assisted enhancement of photoluminescence in combustion derived Li+ co-doped cubic ZrO2:Eu3+ nanophosphors

Red light emitting cubic Zr_0.99Eu_0.01O₂:Li⁺ (0-9 mol%) nanoparticles are synthesized by a low temperature, self-propagating solution combustion method using oxalyl di-hydrazide (ODH) as fuel. In this study, we report systematic investigation of the effect of lithium ion (Li⁺) concentration on the structural properties and the photoluminescence of zirconia. With increasing lithium concentration, the crystallinity of the samples increases and the lattice strain decreases. The higher crystallinity is likely due to charge compensation achieved by replacing one Zr⁴⁺ ion by a Eu³⁺ and a Li⁺ ion. Scanning electron micrographs (SEM) reveal a mesoporous structure characteristic of combustion derived nanomaterials. Photoluminescence (PL) spectra show that the intensity of the red emission (606 nm) is highly dependent on Li⁺ ion concentration. Furthermore there is a promising enhancement in the associated lifetime. Upon Li⁺ doping, the PL intensity of the samples is found to increase by two fold compared to the undoped sample. Variation of PL intensity with Li⁺ concentration is attributed to the differences in probability of non-radiative recombination (relaxing). Intensity parameters (Ω₂, Ω) and radiative properties such as transition rates (A), branching ratios (β), stimulated emission cross-section (σ_e), gain bandwidth (σ_e × Δλ_eff) and optical gain (σ_e × τ) are calculated using the Judd-Ofelt theory. The calculated values suggest that in optimally co-doped samples, in addition to improved crystallinity and charge compensation, the lowering of Eu³⁺ site symmetry and the increase in the covalency of Eu-O bonding due to interstitial Li are responsible for the observed enhancement in PL intensity.

A novel optical thermometry based on the energy transfer from charge transfer band to Eu3+-Dy3+ ions

Optical thermometry based on the up-conversion intensity ratio of thermally coupled levels of rare earth ions has been widely studied to achieve an inaccessible temperature measurement in submicron scale. In this work, a novel optical temperature sensing strategy based on the energy transfer from charge transfer bands of W-O and Eu-O to Eu³⁺-Dy³⁺ ions is proposed. A series of Eu³⁺/Dy³⁺ co-doped SrWO₄ is synthesized by the conventional high-temperature solid-state method. It is found that the emission spectra, emission intensity ratio of Dy³⁺ (572 nm) and Eu³⁺ (615 nm), fluorescence color, lifetime decay curves of Dy³⁺ (572 nm) and Eu³⁺ (615 nm), and relative and absolute sensitivities of Eu³⁺/Dy³⁺ co-doped SrWO₄ are temperature dependent under the 266 nm excitation in the temperature range from 11 K to 529 K. The emission intensity ratio of Dy³⁺ (572 nm) and Eu³⁺ (615 nm) ions exhibits exponentially relation to the temperature due to the different energy transfer from the charge transfer bands of W-O and Eu-O to Dy³⁺ and Eu³⁺ ions. In this host, the maximum relative sensitivity S_r can be reached at 1.71% K⁻¹, being higher than those previously reported material. It opens a new route to obtain optical thermometry with high sensitivity through using down-conversion fluorescence under ultraviolet excitation.

Excitation power dependent population pathways and absolute quantum yields of upconversion nanoparticles in different solvents

The rational design of brighter upconversion nanoparticles (UCNPs) requires a better understanding of the radiationless deactivation pathways in these materials. Here, we demonstrate the potential of excitation power density (P)-dependent studies of upconversion (UC) luminescence intensities, slope factors, and absolute quantum yields (Φ_UC) of popular β-NaYF₄:20% Yb³⁺,2% Er³⁺ UCNPs of different surface chemistries in organic solvents, D₂O, and water as a tool to gain deeper insight into the UC mechanism including population and deactivation pathways particularly of the red emission. Our measurements, covering a P regime of three orders of magnitude, reveal a strong difference of the P-dependence of the ratio of the green and red luminescence bands (I_g/r) in water and organic solvents and P-dependent population pathways of the different emissive energy levels of Er³⁺. In summary, we provide experimental evidence for three photon processes in UCNPs, particularly for the red emission. Moreover, we demonstrate changes in the excited population dynamics via bi- and triphotonic processes dependent on the environment, surface chemistry, and P, and validate our findings theoretically.

Synthesis, structure and multicolor-tunable luminescence of the dandelion-like SiO2:Ln3+ (Ln = Eu, Tb) nanophosphors

Dandelion-like SiO₂:Ln³⁺ (Ln = Eu, Tb) nanophosphors of 70 nm diameter have been synthesized, and colorful emission phosphors were obtained by Ln³⁺ doping.

Upconversion fluorescence imaging of HeLa cells using ROS generating SiO2-coated lanthanide-doped NaYF4 nanoconstructs

Multicolor upconversion of SiO₂-coated nanoparticles using for cells imaging and reactive oxygen species generation.

Photoluminescence properties of Eu3+ ions in yttrium oxide nanoparticles: defect vs. normal sites

The position of activator ions in the lattice has a fundamental effect on the luminescent properties of phosphors.

Sensitized luminescence from water-soluble LaF3:Eu nanocrystals via partially-capped 1,10-phenanthroline: time-gated emission and multiple lifetimes

Novel LaF₃:Eu(5%) nanocrystals containing partially-capped 1,10-phenanthroline ligands have been obtained, which display intense phen-sensitized europium emission in water and multiple lifetimes from Eu³⁺-dopant sites.

Capping ligand infrared absorption and dopant photoluminescence spectroscopy provides a comprehensive picture to probe dopant spatial location in semiconductor nanoparticles

A room temperature based spectroscopic analysis technique assesses the luminescence properties from different spatial location of lanthanide cations in zinc sulfide nanoparticles.

Multifunctional luminescent nanomaterials from NaLa(MoO4)2:Eu(3+)/Tb(3+) with tunable decay lifetimes, emission colors, and enhanced cell viability

A facile, but effective, method has been developed for large-scale preparation of NaLa(MoO4)2 nanorods and microflowers co-doped with Eu(3+) and Tb(3+) ions (abbreviated as: NLM:Ln(3+)). The as-synthesized nanomaterials possess a pure tetragonal phase with variable morphologies from shuttle-like nanorods to microflowers by controlling the reaction temperature and the amount of ethylene glycol used. Consequently, the resulting nanomaterials exhibit superb luminescent emissions over the visible region from red through yellow to green by simply changing the relative doping ratios of Eu(3+) to Tb(3+) ions. Biocompatibility study indicates that the addition of NLM:Ln(3+) nanomaterials can stimulate the growth of normal human retinal pigment epithelium (ARPE-19) cells. Therefore, the newly-developed NaLa(MoO4)2 nanomaterials hold potentials for a wide range of multifunctional applications, including bioimaging, security protection, optical display, optoelectronics for information storage, and cell stimulation.

A novel approach to prepare optically active ion doped luminescent materials via electron beam evaporation into ionic liquids

A novel approach to prepare luminescent materials via electron-beam evaporation into ionic liquids is presented which even allows doping of host lattices with ions that have a strong size mismatch. To prove this, MgF2 nanoparticles doped with Eu(3+) were fabricated. The obtained nanoparticles featured an unusually high luminescence lifetime and the obtained material showed a high potential for application.

A novel deep photodynamic therapy modality combined with CT imaging established via X-ray stimulated silica-modified lanthanide scintillating nanoparticles

A novel theranostic nanosystem was establishedviaX-ray excited LaF₃:Tb scintillating nanoparticles capable of deep-seated tumour photodynamic therapy.

Europium-doped LaF3nanocrystals with organic 9-oxidophenalenone capping ligands that display visible light excitable steady-state blue and time-delayed red emission

Visible light excitable 9-oxidophenalenone-coated LaF₃:Eu NCs display steady-state blue and time-delayed red emission; capping ligands act as probes to reveal three different Eu³⁺sites with distinct emission properties.

Regulated morphology/phase structure and enhanced fluorescence in YF3:Eu3+,Bi3+via a facile method

Using a facile method to regulate morphology/phase structure and significantly enhance the fluorescence in YF₃:Eu³⁺,Bi³⁺.

Photoluminescence and photocatalytic activity of monodispersed colloidal “ligand free Ln3+-doped PbMoO4 nanocrystals”

Ligand free monodisperse Ln³⁺ doped PbMoO₄ nanocrystals as efficient photocatalyst and phosphor.

C-dot sensitized Eu3+ luminescence from Eu3+-doped LaF3–C dot nanocomposites

C-dot sensitized strong Eu³⁺ luminescence is observed in Eu³⁺-doped LaF₃–C-dot nanocomposites via energy transfer.

Influence of silicate sol–gel host matrices and catalyst agents on the luminescent properties of Eu3+/Gd3+ under different excitation wavelengths

Sol–gel silicate glasses co-doped with Gd³⁺ and Eu³⁺ ions were successfully obtained and the pronounced effect of the matrix composition on the luminescent properties and energy transfer process from Gd³⁺ to Eu³⁺ was confirmed.

Lanthanide-based heteroepitaxial core-shell nanostructures: compressive versus tensile strain asymmetry

Heteroepitaxial core-shell nanostructures have been proven advantageous in a wide variety of applications, ranging from luminescence enhancement, band gap engineering, multimodal theranostics, to catalysis. However, precisely tailoring the epitaxial growth is challenging, and a general understanding of the parameters that impact epitaxial growth remains unclear. Here we demonstrate the critical role of the sign of the lattice mismatch of the shell relative to the core (compressed/tensile) in generating lanthanide-based core-shell structures, a parameter conventionally not considered in heteroepitaxial design. We took advantage of the very gradual contraction of lanthanide ions along the series to control precisely both the magnitude and the sign of lattice mismatch and investigated multiple sodium lanthanide fluoride (NaLnF4) core-shell heterostructures of variable composition and size. We discovered that the tensile strained shells adapt to the core crystallite shape (i.e., conformal) and lattice structure (i.e., coherent), while under identical magnitude of mismatch, the compressively strained shells are neither conformal nor coherent to the core. This striking asymmetry between the tensile and compressively strained epitaxial growth arises from the fundamental anharmonicity of the interatomic interactions between the attractive and repulsive pairs. From a broader perspective, our findings redefine the a priori design consideration and provide a fundamental insight on the necessity to include the sign of lattice mismatch and not just its magnitude in designing heteroepitaxial core-shell nanostructures.

Microwave synthesis, photoluminescence, and photocatalytic activity of PVA-functionalized Eu3+-doped BiOX (X = Cl, Br, I) nanoflakes

We report a facile microwave-assisted green synthetic route for colloidal poly(vinyl alcohol) (PVA)-coated europium (Eu(3+))-doped luminescent heavy metal bismuth oxyhalide (BiOX; X = Cl, Br, I) nanoflakes at low temperature and examine their structural, optical, and photocatalytic characteristics. PVA coating onto the surface of the nanoflakes endows them with hydrophilic nature. Both Eu(3+)-doped BiOCl and BiOBr nanoflakes exhibit strong optical properties related to Eu(3+) and Bi(3+) which are quenched in case of Eu(3+)-doped BiOI matrix. These results are supported by Eu(3+) photoluminescence lifetime values of 0.61 ms, 0.59 ms, and 8.9 μs, respectively. The former two matrices have quite similar crystal field environments as deduced from the asymmetric ratios of (5)D0 → (7)F2 (614 nm) and (5)D0 → (7)F1 (591 nm) transitions. In addition to possessing interesting photoluminescence properties, a comparison of the photocatalytic activity of Eu(3+)-doped BiOX (X = Cl, Br, I) nanoflakes, with corresponding estimated band gaps of 3.36, 2.74, and 1.67 eV has been evaluated using Rhodamine B (RhB) dye under visible light irradiation. The nanoflakes exhibited 100% dye degradation under visible light irradiation. Eu(3+)-doped BiOCl nanoflakes manifested higher photocatalytic efficiency compared to the other matrices following apparent first-order kinetics. Such a boost in efficiency is attributed to their high surface area to volume ratios, layered crystalline structures, indirect band gap nature, and ability to utilize broad bands in the solar spectrum.

Highly luminescent lanthanide fluoride nanoparticles functionalized by aromatic carboxylate acids

The photoluminescent spectra of LaF₃:8% Tb³⁺, SA-LaF₃:8% Tb³⁺ and SSA-LaF₃:8% Tb³⁺ nanoparticles, and the photographs in water (SSA-LaF₃:8% Tb³⁺) and as powder (SA-LaF₃:8% Tb³⁺) under 254 nm excitation, respectively.

Photoluminescence of cerium fluoride and cerium-doped lanthanum fluoride nanoparticles and investigation of energy transfer to photosensitizer molecules

Ce_xLa_1−xF₃ nanoparticles have been proposed for use in nanoscintillator–photosensitizer systems, aiming to combine the effects of radiotherapy and photodynamic therapy.

Bilayer stabilized Ln3+-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 Ln³⁺-doped CaMoO₄ nanocrystals (Ln³⁺ = Eu³⁺, Er³⁺/Yb³⁺).