The standard and anomalous crystal-field spectra of Eu3+

Energy transfer dynamics and luminescence properties of Eu3+ in CaMoO4 and SrMoO4

Undoped and europium doped CaMoO₄ and SrMoO₄ scheelites are synthesized using a complex polymerization method.

Lanthanide-doped upconversion nano-bioprobes: electronic structures, optical properties, and biodetection

The latest advances in lanthanide-doped upconversion nanoparticles were comprehensively reviewed, which covers from their fundamental photophysics to biodetection.

Molten salt synthesis, visible and near-IR region spectral properties of europium or neodymium doped CoNb2O6 columbite niobate

Emission spectra of the phosphor powders for the ⁵D₀→⁷F₂ transition in CoNb₂O₆ powders doped with Eu³⁺ at 300 K.

Dual emission tunable in the near-infrared (NIR) and visible (VIS) spectral range by mix-LnMOF

In this study, we describe the synthetic approach, crystallographic structure, luminescent behavior in heteronuclear coordination polymers with emission in the visible (Eu³⁺ and organic ligand) and near-infrared (Nd³⁺) range.

The role of reaction conditions in the polymorphic control of Eu3+ doped YInO3: structure and size sensitive luminescence

Controlled synthetic conditions yielded YInO₃:Eu³⁺ in both C-type and hexagonal modifications which exhibited a tremendous bearing of size and local structure on Eu³⁺ luminescence, all in a single compound.

An insight into local environment of lanthanide ions in Sr2SiO4:Ln (Ln = Sm, Eu and Dy)

Site occupancy of Eu²⁺, Eu³⁺, Sm³⁺ and Dy³⁺ is investigated in Sr₂SiO₄ using TRFS and EXAFS and complemented by DFT calculations.

Photoluminescence and doping mechanism of theranostic Eu3+/Fe3+ dual-doped hydroxyapatite nanoparticles

Theranostic nanoparticles currently have been regarded as an emerging concept of 'personalized medicine' with diagnostic and therapeutic dual-functions. Eu3+ doped hydroxyapatite (HAp) has been regarded as a promising fluorescent probe for in vivo imaging applications. Additionally, substitution of Ca2+ with Fe3+ in HAp crystal may endow the capability of producing heat upon exposure to a magnetic field. Here we report a preliminary study of doping mechanism and photoluminescence of Eu3+ and Fe3+ doped HAp nanoparticles (Eu/Fe:HAp). HAp with varied concentration of Eu3+ and Fe3+ doping are presented as Eu(10 mol%):HAp, Eu(7 mol%)-Fe(3 mol%):HAp, Eu(5 mol%)-Fe(5 mol%):HAp, Eu(3 mol%)-Fe(7 mol%):HAp, and Fe(10 mol%):HAp in the study. The results showed that the HAp particles, in nano-size with rod-like morphology, were successfully doped with Eu3+ and Fe3+, and the particles can be well suspended in cell culture medium. Photoluminescence analysis revealed that particles have prominent emissions at 536 nm, 590 nm, 615 nm, 650 nm and 695 nm upon excitation at a wavelength of 397 nm. Moreover, these Eu/Fe:HAp nanoparticles belonged to B-type carbonated HAp, which has been considered an effective biodegradable and biocompatible drug/gene carrier in biological applications.

Local structural investigation of Eu(3+)-doped BaTiO3 nanocrystals

A structural investigation of sub-15 nm xEu:BaTiO3 nanocrystals (x = 0-5 mol%) was conducted to determine the distribution of the Eu(3+) ion in the BaTiO3 lattice. Pair distribution function analysis of X-ray total scattering data (PDF), steady-state photoluminescence, and X-ray absorption spectroscopy (XANES/EXAFS) were employed to interrogate the crystal structure of the nanocrystals and the local atomic environment of the Eu(3+) ion. The solubility limit of the Eu(3+) ion in the nanocrystalline BaTiO3 host synthesized via the vapor diffusion sol-gel method was estimated to be ∼4 mol%. A contraction of the perovskite unit cell volume was observed upon incorporation of 1 mol% of europium, while an expansion was observed for nominal concentrations between 1 and 3 mol%. The average Eu-O distance and europium coordination number decreased from 2.46 Å and 9.9 to 2.42 Å and 8.6 for europium concentrations of 1 and 5 mol%, respectively. Structural trends were found to be consistent with the substitution of Eu(3+) for Ba(2+)via creation of a Ti(4+) vacancy at low europium concentrations (<1 mol%), and with the substitution of Eu(3+) for both Ba(2+) and Ti(4+) at high europium concentrations (1-3 mol%). The significance of accounting for local structural distortions to rationalize the distribution of lanthanide ions in the perovskite host is highlighted.

Supramolecular luminescent hydrogels based on β-amino acid and lanthanide ions obtained by self-assembled hydrothermal reactions

Hydrothermal synthesis of four new supramolecular hydrogels based on lanthanide ions with promising properties for RGB systems.

Unusual photoluminescence properties of the 3D mixed-lanthanide–organic frameworks induced by dimeric structures: a theoretical and experimental approach

Experimental and theoretical investigation of the 3D Ln-MOFs that present singular spectral signature.

Lanthanide-doped luminescent nano-bioprobes: from fundamentals to biodetection

Trivalent lanthanide (Ln(3+))-doped luminescent inorganic nanoparticles (NPs), characterized by long-lived luminescence, large Stokes and/or anti-Stokes shifts, narrow emission bands and high photochemical stability, are considered to be promising candidates as luminescent bioprobes in biomedicine and biotechnology. In this feature article, we provide a brief overview of the most recent advances in Ln(3+)-doped luminescent inorganic NPs as sensors, which covers from their chemical and physical fundamentals to biodetection, such as controlled synthesis methodology, surface modification chemistry, optical physics, and their promising applications in diverse bioassays, with an emphasis on heterogeneous and homogeneous in vitro biodetection. Finally, some of the most important emerging trends and future efforts toward this active research field are also proposed.

Optical properties of Eu³+ ions in phosphate glasses

Eu(3+)-doped phosphate (P(2)O(5)+K(2)O+SrO+Al(2)O(3)+Eu(2)O(3)) glasses with varying Eu(2)O(3) concentration have been prepared by standard melt quenching technique and are characterized through various spectroscopic techniques at room temperature. Luminescence spectra of these glasses exhibit the characteristic emission of Eu(3+) ion with an intense and most prominent red emission attributed to (5)D(0)→(7)F(2) transition. Crystal-field analysis has been carried out to estimate the local symmetry in the vicinity of Eu(3+) ions. Judd-Ofelt parameters have been evaluated from the luminescence intensity ratios of (5)D(0)→(7)F(J) (J=2, 4 and 6) to (5)D(0)→(7)F(1) transitions as well as absorption spectrum under different constraints. Decay rates for the (5)D(0) level of Eu(3+) ions have been recorded by monitoring the emission at around 609 nm corresponding to (5)D(0)→(7)F(2) transition. The experimental lifetime for the (5)D(0) level in title glasses is independent of Eu(3+) ion concentration.

Effect of pH on the synthesis and properties of luminescent SiO2/calcium phosphate:Eu3+ core-shell nanoparticles

A novel method for the synthesis of luminescent SiO(2)/calcium phosphate (CaP):Eu(3+) core-shell nanoparticles (NPs) was developed via a sol-gel route followed by annealing at a temperature of 800 °C. The object of this study was the investigation of the effect of pH on the formation of a CaP shell around the silica core. The resulting annealed NPs exhibited an amorphous SiO(2) core and a crystalline luminescent shell. The formation of a CaP layer was possible at pH below 4.5 and above 6.5 during the coating step. The crystal structure of the shell was studied by X-ray diffraction analysis. Hydroxyapatite (HAp) and α-tricalcium phosphate were detected as crystal phases of the surrounding layer. However, NPs produced under basic conditions exhibited a higher crystallinity of the CaP layer than did samples coated at pH below 4.5. In the pH interval between 4.5 and 6.5, no shell growth but the formation of secondary NPs containing CaO and Ca(OH)(2) was observed. Furthermore, SiO(2)/CP:Eu(3+) core-shell NPs were investigated by transmission electron microscopy, dynamic light scattering, Fourier transform infrared spectroscopy, inductively coupled plasma optical emission spectrometry, and photoluminescence spectroscopy. The resulting HAp-coated NPs were successfully tested by a cell-culture-based viability assay with respect to a later application as a luminescent marker for biomedical applications.

Eu3+ doped KYF4 nanocrystals: synthesis, electronic structure, and optical properties

Monodisperse cubic-phase KYF(4) : Eu(3+) nanocrystals (NCs) were synthesized via a modified thermal decomposition method. The optical properties of Eu(3+) in KYF(4) NCs including multiple luminescence centers, site symmetry, luminescence dynamics, as well as crystal-field levels of Eu(3+) were investigated in detail based on high-resolution photoluminescence (PL) spectroscopy at low temperature (10 K). Different from Eu(3+) in bulk counterparts, multiple sites of Eu(3+) in KYF(4) NCs were revealed by using the luminescence of Eu(3+) as a sensitive structural probe. The highest site symmetry of Eu(3+) at new near-surface site was deduced to be distorted from O(h) to D(2) (or C(2v)). Due to a small filling factor (0.45) of NCs, the PL lifetime of (5)D(0) of Eu(3+) in KYF(4) NCs was much longer than that in bulk counterparts, which was found to be significantly affected by the surrounding medium around the NCs.

Optical properties and luminescence dynamics of Eu3+-doped terbium orthophosphate nanophosphors

The development of luminescent inorganic nanocrystals (NCs) doped with rare-earth (RE) ions has attracted increasing interest owing to their distinct optical properties and versatile applications in time-resolved bioassays, multiplex biodetection, DNA hybridization and bioimaging. Hexagonal TbPO4:Eu3+ NCs (10-30 nm) were synthesized via a facile hydrothermal method assisted with oleic acid (OA) surfactants, which exhibit tunable emissions from green to red by varying the concentration of Eu3+. The Tb3+-to-Eu3+ energy transfer efficiency observed reaches up to 94%. Different from their bulk counterparts, a new interface-state band (316 nm) in addition to the commonly observed spin-forbidden 4f-5d transition band (265 nm) of Tb3+ was found to be dominant in the excitation spectrum of NCs due presumably to the formation of surface TbPO4/OA complexes, which provides an additional excitation antenna in practical utilization. Two kinds of luminescence sites of Eu3+ in TbPO4 NCs, with the site symmetry of C2 or C1, were identified based on the emission spectra at 10 K and room temperature. Furthermore, the photoluminescence (PL) dynamics of Tb3+ ions in pure TbPO4 NCs have been revealed. Compared to the exponential PL decay in bulk counterparts induced by very fast energy migration, the non-exponential decay from 5D4 of Tb3+ in TbPO4 NCs is mainly attributed to the diffusion-limited energy migration due to more rapid energy transfer from Tb3+ to defects than the energy migration among Tb3+.

Luminescence enhancement and quenching by codopant ions in lanthanide doped fluoride nanocrystals

Luminescence enhancement (LE) and quenching for lanthanide (Ln) doped nanocrystals is obtained by a second Ln(3+) ion doping method. Singly or doubly doped LaOF, LaF(3) and NaYF(4) nanocrystals are studied in detail under selective or two-color excitations. The underlying reason for LE by codoping is explored, and a mechanism of the enhancement based on the low local point symmetry effect of the matrix is proposed. It is found that the modification of the local environment induced by dopant ions can result in LE if the non-radiative relaxation probability can be ignored. The observations reported here should be useful for improving the quality of Ln(3+) doped nanomaterials.

Eu3+-doped β-Ga2O3 nanophosphors: annealing effect, electronic structure and optical spectroscopy

A comprehensive survey of electronic structure and optical properties of rare-earth ions-doped semiconductor is of vital importance for their potential applications. In this work, Eu(3+)-doped β-Ga(2)O(3) nanocrystals were synthesized via a combustion method. The evolution of the optical properties of nanophosphors with increasing the annealing temperature was investigated in detail by means of excitation and emission spectra at room temperature and 10 K. Eu(3+) ions were proved to be incorporated into the crystal lattice of the β-Ga(2)O(3) phase after annealing the as-prepared nanoparticles at 1100 °C. It was observed that the substitution of Eu(3+) for Ga(3+) occurred at merely single site, in spite of two crystallographically nonequivalent sites of Ga(3+) in β-Ga(2)O(3). Spectroscopic evidence corroborated and clarified the local symmetry of C(s) for Eu(3+) at this single site. From the high-resolution excitation and emission spectra, 71 crystal-field levels of Eu(3+) in β-Ga(2)O(3) were identified and analyzed in terms of 19 freely varied free-ions and crystal-field parameters based on C(s) symmetry. The standard deviation of the final fitting is as low as 12.9 cm(-1), indicating an excellent agreement between experimental and calculated energy levels. The temperature-dependent luminescence dynamics of the (5)D(0) multiplet for Eu(3+) in β-Ga(2)O(3) phosphors has also been revealed for the first time from 10 to 300 K.

Molecule-like Eu3+-dimers embedded in an extended system exhibit unique photoluminescence properties

Much is known about the photoluminescence of lanthanide-containing systems, particularly amorphous silicates or organic-inorganic hybrids and crystalline metal-organic frameworks. Comparatively, stoichiometric microporous Ln-silicates are poorly studied. Here, we report the exceptional photoluminescence of microporous AV-24, K(7)[Ln(3)Si(12)O(32)] x xH(2)O (Ln(3+) = Sm(3+), Eu(3+), Gd(3+), Tb(3+)), the first silicate possessing Ln(3+)-O-Ln(3+) dimers (inter-Ln distance ca. 3.9 A), i.e., two edge-sharing {LnO(6)} octahedra embedded in a crystalline matrix. It is totally unprecedented that in AV-24 Eu(3+)-O-Eu(3+) dimers behave like discrete entities, i.e., molecules: they (i) have a unique emission signature, with pseudopoint group symmetry (C(i)), different from the symmetry (C(1)) of each individual constituent Eu(3+) ion, and (ii) exhibit the unusually long (5)D(0) lifetime of 10.29 ms (12 K). In accord with the experimental evidence, a molecular orbital model shows that the Eu(3+)-O-Eu(3+) dimers are energetically more stable than the individual metal ions.

Dependence of Charge Transfer Energy on Crystal Structure and Composition in Eu3+-Doped Compounds

We report a method for estimating the positions of charge transfer (CT) bands in Eu3+-doped complex crystals. The environmental factor (h(e)) influencing the CT energy is presented. h(e) consists of four chemical bond parameters: the covalency, the bond volume polarization, the presented charge of the ligand in the chemical bond, and the coordination number of the central ion. These parameters are calculated with the dielectric theory of complex crystals. The relationship between the experimental CT energies and calculated environmental factors was established by an empirical formula. The calculated values are in good agreement with the experimental results. Such a relationship was confirmed by detailed analysis. In addition, our method is also useful to predict the charge-transfer position of any other rare earth ion.