High Luminescence Intensity Research Articles

Visible and near-infrared luminescent properties of Pr3+ doped strontium molybdate thin films by a facile polymer-assisted deposition process

Quartz substrate supported Praseodymium (Pr) doped strontium molybdate (SrMoO4) thin films with good uniformity and outstanding fluorescent properties are successfully fabricated via a facile polymer-assisted deposition (PAD) method. In combination with the strong chelating effect of water-soluble polymer on metal cations, the free cations without chelating are effectively ruled out but the remaining chelating metal cations are employed for the highly uniform and accurate stoichiometry luminescent SrMoO4: Pr thin films, layer-by-layer mounting on the common quartz substrates. More importantly, the excellent release of stress from polymer during the growth process of epitaxial thin film can effectively overcome the mismatch between thin film and common quartz substrate and then guarantee the quality of thin film. Under the ultraviolet (UV) light excitation, the samples show high luminescence intensity both in visible and near-infrared (NIR) regions peaked at 646 nm and 1037 nm, mainly ascribing to the transitions of 3P0 → 3F2 and 1G4 → 3H4 of Pr3+ ions. The luminescent properties can be tailored by optimizing the number of spin-coated layers and doping concentrations. The maximum emission occurs at 4 mol% of Pr3+ dopant, and it exhibits an impressive high photoluminescence quantum yield (QY) of up to 86.12%. These results evidently demonstrate the present PAD method is a useful prototype for preparing high performance luminescent thin films even on the cheap quartz substrate.

Design optimisation of C ion implantation of α-Al2O3 for medical dosimetry

The present work reports the fabrication and characterization of α–Al2O3:C, a highly sensitive low effective atomic number (Zeff = 10.7) OSL material for medical dosimetry, through a new approach of doping via implantation. In this study, a Single Crystalline α–Al2O3 (SCALO) and a Sapphire α–Al2O3 (SALO) are used and implanted with 100 keV of C+ at various fluences (mol%) from 2.5 × 1014 ions cm−2 (~0.04%) to 6.25 × 1015 ions cm−2 (~1%) and are pre-heated up to 220 °C. The structural, optical, morphological and luminescent studies of the Carbon doped α–Al2O3 (α–Al2O3:C) are carried out using X-ray diffraction, Ultraviolet-visible spectroscopy (UV–Vis), Photo-luminescence (PL), Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS), Optically Stimulated Luminescence (OSL), and Thermo-Luminescence (TL). The doping of ~1 mol% of C+ is found at an optimized doping level due to its high intensity of luminescence. This phenomenon is studied for heavy charged particle (HCP) dosimetry, which might prove effective for cancer treatment. It is found that α –ALO:C (both the single crystalline and the sapphire alumina) has the capability to measure large radiation doses (~kGy). This is attributed to the generation of stable defects after the incorporation of Carbon that results in a linear response with the dose and in extraordinary efficiency. Thus, this study confirms the development of α–Al2O3 by the novel approach of C+ implantation method and the findings result in an efficient medical radiation dosimeter.

Upconversion/Downconversion luminescence and preparation of NIR-to-UV-excited Gd2O2S:Er phosphor

Efficient conversion of ultraviolet (UV) and near-infrared (NIR) radiations to visible emissions were carried out through Gd2O2S:Er phosphor synthesized by solid-state reaction method in vacuum. The spectra study of Gd2O2S:Er phosphor was performed as a function of firing temperature under the excitation wavelengths of 379 and 980 nm, respectively. The emission bands in visible light region corresponding to the transitions between 2H9/2 → 4I15/2 (412 nm), 4F7/2 → 4I15/2 (488 nm), 2H11/2 → 4I15/2 (531 nm), 4S3/2 → 4I15/2 (554 nm) and 4F9/2 → 4I15/2 (670 nm) were demonstrated. Color emission can be tuned from red to green due to Er3+ ions doping by varying the firing temperature under 379 nm UV light excitation. First principles calculation results indicated that crystallographic plane of (101) has higher absorption efficiency than the crystallographic plane of (100) thus to result in higher luminescent intensity.

Temperature-dependent OSL properties of nano-phosphors LiAlO2:C and α-Al2O3:C

The present study focuses on the synthesis and characterization of carbon doped nano-phosphors, LiAlO2 and α-Al2O3 and their temperature-dependent optically stimulated luminescence (TA-OSL) characteristics in the temperature ranges of 25–350 °C. These nano-phosphors with the carbon concentration of 0.01 mol% exhibits high luminescent intensity for LiAlO2:C in the low dose range of 1 mGy-7 Gy and for α-Al2O3:C in the range of 100 mGy-1 kGy. Both these nano-phosphors are of polycrystalline in nature, having grain size 15–50 nm as confirmed by the X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM), respectively. The maximum TA-OSL intensities are observed at 125 °C for LiAlO2:C and 200 °C for Al2O3:C, and reveal the presence of deep defect centres. The Arrhenius analysis shows the activation energies Ea = 0.06 ± 0.02 eV for LiAlO2:C and Ea = 0.04 ± 0.01 eV, & Eb = 0.48 ± 0.07 eV for Al2O3:C. The TA-OSL and OSL characteristics are discussed with special reference to the medical and high radiation dosimetry. These compounds, LiAlO2:C and α-Al2O3:C, are non-toxic, robust and are potential candidates for reusable dosimetry.

Synthesis and characterisation of human serum albumin passivated CdTe nanocrystallites as fluorescent probe

The II–VI nanocrystallites (NCs) are well known as a great fluorescent probe, but one of the main problem is a toxic effect. Covering a semiconductor NCs by some materials or chemicals can reduce it, but change optical properties and functional characteristics of NCs. The potential ability of the CdTe NCs passivated by human serum albumin (HSA) to cancer cells bioimaging is examined. Performed research explored the interaction between the CdTe NCs and HSA, and fluorescence imaging efficiency of the NC–HSA bionanocomplex in comparison with the uncovered NCs. The secondary structure of the HSA is similar to the native form, which suggests a biocompatibility of the prepared bionanocomplex. The CdTe NCs located in osteosarcoma cancer cells show a high luminescence intensity. The light emission of the CdTe NCs connected with albumin is less than the pure NCs, but it is still satisfactory, and additionally have high resistance to photo-bleaching. It suggests that the CdTe NC–HSA bionanocomplex can be used as a fluorescent probe for cell labelling, tracking and other bioimaging applications.

Coordination Geometry‐Dependent Multi‐Band Emission and Atypically Deep‐Trap‐Dominated NIR Persistent Luminescence from Chromium‐Doped Aluminates

AbstractAn abnormal trap distribution and coordination geometry‐dependent multi‐band emission are discovered in chromium‐doped aluminates. The multi‐band and broadband persistent luminescence from 650–1100 nm peaking at 688 and 793 nm from Cr3+‐doped SrAl12O19 is systematically studied via structural and spectroscopic analysis. Solid state nuclear magnetic resonance allows the visualization of various coordination configurations in SrAl12O19, thus offering the possibility of tailoring the local geometry of the emission center to trigger the control of the spectral parameter. Deep tissue ex vivo and in vivo imaging in mice both demonstrate that multi‐band‐emissive SrAl12O19:Cr3+ shows superior, high‐quality near‐infrared (NIR) bio‐imaging in the biological transparency window compared to single band‐emissive (with emission only at 688 nm) SrAl2O4:Cr3+, although SrAl2O4:Cr3+ has a higher luminescent intensity and longer duration at 688 nm. Moreover, by measuring the thermoluminescence spectra the driving force of carrier release is discovered to be only from the deep trap (the depth is > 1 eV), which is different from the generally accepted shallow‐dependent afterglow‐emitting process. These findings pave the way for opening a vista of possible avenues for the enhancement of signal‐to‐noise ratio, the improvement of imaging quality, as well as the understanding of the trapping and de‐trapping process in long‐persistent phosphors.

Effect of W6+ dopant on the morphology and luminescence properties of NaLa(MoO4)2: Eu3+ phosphors

W6+ dopant on the NaLa(MoO4)2:Eu3+ solid solution phosphors with various shapes have been synthesized via the hydrothermal method without using any structural modifier and organic solvents. The morphology and luminescence properties of W6+ doped NaLa(MoO4)2:Eu3+ phosphors are obtained and characterized by SEM and PL/PLE spectra. Both morphology and luminescence properties are considered to manipulate by the mole ratio of W/Mo. By increasing the W6+ amount, particle shapes are changed from rice-shaped particles to spindle-shaped, cocoon-shaped, then to layers of octahedron-shaped. Under UV light excitation, all samples show bright red light due to the characteristic 4f-4f transitions of Eu3+. Tungstate and molybdate phosphors have higher luminescence intensity than that of tungstate and molybdate solid solution phosphors.

Emission-spectrum-shape-evolution of Eu2+ under the crystallization process of the host-Ca2AlMg0.5Si1.5O7

The Eu2+-doped phosphor has been regarded as one of potential luminescent materials, which show broad emission through 4f7(7S7/2)-4f6(7FJ)5d1 transition of Eu2+ activator strongly coupled with the host lattice. In addition, the emission spectra shape can be adjusted via changing the crystal-field of host, covalence, symmetry of the sites, coordination number of activator and so on. We employ a home designed preparation route to synthesize a monodisperse microsphere phosphor series sintered at different temperature and use a combination of structural, morphological and optical characterization techniques to understand the emission-spectrum-shape-evolution mechanism of Eu2+ in the gradual change of CAMS host. We observe that the intermediate CAMS: Eu2+ phosphor sintered at 1200 ℃ has the highest luminescent intensity and broader cover region of emission spectrum, while the intensity reduces and the cover region shrinks as the sintering temperature increasing from 1200 ℃ to 1400 ℃. The energy transfer aggravation and the cover region narrow with the sintering temperature increasing, which is closely related to the complete degree of the host crystal.

Luminescent biomimetic citrate-coated europium-doped carbonated apatite nanoparticles for use in bioimaging: physico-chemistry and cytocompatibility.

Nanomedicine covers the application of nanotechnologies in medicine. Of particular interest is the setup of highly-cytocompatible nanoparticles for use as drug carriers and/or for medical imaging. In this context, luminescent nanoparticles are appealing nanodevices with great potential for imaging of tumor or other targetable cells, and several strategies are under investigation. Biomimetic apatite nanoparticles represent candidates of choice in nanomedicine due to their high intrinsic biocompatibility and to the highly accommodative properties of the apatite structure, allowing many ionic substitutions. In this work, the preparation of biomimetic (bone-like) citrate-coated carbonated apatite nanoparticles doped with europium ions is explored using the citrate-based thermal decomplexing approach. The technique allows the preparation of the single apatitic phase with nanosized dimensions only at Eu3+ doping concentrations ≤0.01 M at some timepoints. The presence of the citrate coating on the particle surface (as found in bone nanoapatites) and Eu3+ substituting Ca2+ is beneficial for the preparation of stable suspensions at physiological pH, as witnessed by the ζ-potential versus pH characterizations. The sensitized luminescence features of the solid particles, as a function of the Eu3+ doping concentrations and the maturation times, have been thoroughly investigated, while those of particles in suspensions have been investigated at different pHs, ionic strengths and temperatures. Their cytocompatibility is illustrated in vitro on two selected cell types, the GTL-16 human carcinoma cells and the m17.ASC murine mesenchymal stem cells. This contribution shows the potentiality of the thermal decomplexing method for the setup of luminescent biomimetic apatite nanoprobes with controlled features for use in bioimaging.

Highly sensitive Eu3+ doped in sol-gel matrix optical sensor for the assessment of Ciprofloxacin in different real samples

The efficiency of excited-state interaction between Eu3+ doped in sol- gel matrix and the industrial product ciprofloxacin of (CFX) has been studied in different solvent and pHs. A high luminescence intensity peak at 617 nm of europium- ciprofloxacin complex at λex=365 nm in acetonitrile was obtained. The photophysical properties of the red emissive Eu3+ complex doped in sol-gel matrix have been elucidated, the europium was used as optical sensor for the assessment of ciprofloxacin in the pharmaceutical tablets and serum samples at pH 8.0 and λex = 365 nm with a concentration range of 5.0 ×10−9 - 1.0 ×10−6 mol L−1 for ciprofloxacin, correlation coefficient of 0.99 and detection limit of 1.65 ×10−9 mol L−1.

Precipitation and tunable emission of cesium lead halide perovskites (CsPbX3, X = Br, I) QDs in borosilicate glass

In prior work, fully inorganic perovskite nanocrystals of cesium lead halide (CsPbX3, X = Cl, Br, I), representing bright and tunable photoluminescence, have been synthesized using hot-inject approach and anion exchange reaction. Regrettably, the air instability and poor water resistant properties still hindered its application owing to their extremely fast reaction kinetics and easy anion exchange. Herein, we report a facile melting–quenching technique of CsPbX3 (X = Br, I) quantum dots (QDs) glass, and it also shows a tunable photoluminescence (520–698nm) controlled by the molar ratios of halide precursors. This melting–quenching CsPbX3 QDs glass exhibits high luminescent intensity, narrow photoluminescence (PL) emission, including the similar bandgap energies as CsPbX3 QDs solution. The chemical stability and tunable emission make perovskite QDs glass appealing for lighting display, particularly for warm lighting source, which realize the application of solid-state lighting for CsPbX3 QDs.

Near UV excitable Eu-doped alumina nanophosphors synthesized by the microwave assisted solvothermal technique

Europium doped alumina nanophosphors have been synthesized by the microwave assisted solvothermal technique. The dependence of the photoluminescence response and structural features of these nanophosphors on the europium content and annealing temperature has been characterized for a wide range of compositions and thermal treatments. The nanophosphors are composed of a mixture of nanocrystalline γ-Al2O3 and EuAlO3, in addition to an amorphous alumina phase. The relative quantities of each phase depend on both the europium content and the annealing temperature. High europium content and/or annealing temperature lead to larger fractions of EuAlO3 nanocrystals having with poor luminescence characteristics, while lower temperatures and europium contents result in the predominance of γ-Al2O3 nanocrystals and amorphous alumina, showing much more efficient luminescent emission. The luminescence spectra from all samples show the characteristic red emission peaks from the Eu3+ ion associated with inter-electronic energy level transitions. However, the excitation spectra in these nanophosphors are dominated, by the 7F0–5L6 transition (395 nm), as opposed to the dominant charge-transfer related band at ~260 nm commonly reported for this material. The highest luminescence intensity was obtained for nanophosphors doped with 7.5 at.% of Eu, annealed at 900 °C, which exhibits a quantum yield of 45% when excited with 395 nm light.

Kiwifruit-like Persistent Luminescent Nanoparticles with High-Performance and in Situ Activable Near-Infrared Persistent Luminescence for Long-Term in Vivo Bioimaging.

Persistent luminescence nanoparticles (PLNPs) have great potential for bioimaging because they can eliminate the tissue autofluorescence and improve the signal-to-noise ratio significantly. High-temperature calcination is a necessary process for the PLNPs to achieve high luminescence intensity and long afterglow time. However, high-temperature calcination usually results in uncontrollable morphology and poor homogeneity of PLNPs, which greatly limit their applications. Therefore, there is still a high demand to find a suitable method for synthesizing PLNPs with high luminescence intensity and long afterglow time while maintaining their monodispersed morphology. Herein, we report a facile silica template method to synthesize PLNPs with a kiwifruit-like structure that can tolerate high-temperature calcination. The as-prepared kiwifruit-like SiO2@ZnGa2O4:Cr3+@SiO2 PLNPs have enhanced near-infrared persistent luminescence, uniform morphology and size, and good biocompatibility. Moreover, the SiO2@ZnGa2O4:Cr3+@SiO2 PLNPs can be repeatedly activated by soft X-rays in situ and emit near-infrared persistent luminescence with long decay time, holding great potential for deep-tissue and long-term in vivo bioimaging. We believe that this study will open new perspectives for synthesizing high-performance PLNPs for optical imaging and diversified applications.

Luminescence and energy transfer in Dy3+/Eu3+ co-doped aluminosilicate oxyfluoride glasses and glass-ceramics

A series of oxyfluoride glasses with the composition SiO2–CaF2–Al2O3–CaO, doped with Dy2O3 (0.5–1 mol%) and Eu2O3 (0–4 mol%), have been prepared using the melt quenching method. The glass-ceramics have been obtained by heating the as-made glasses at 680 °C and 750 °C for 1 h. The glasses and the glass-ceramics were investigated using photoluminescence techniques in the near-UV and visible ranges, and differential thermal analysis (DTA) and x-ray diffraction (XRD) measurements were performed. The samples doped with 0.5 mol% Dy3+ were observed to have the highest luminescence intensity under 453 nm excitation compared to the samples doped with 1 mol% Dy3+ and the co-doped samples. The increased luminescence intensity could be caused by energy transfer between rare-earth (RE) ions and cross-relaxation of Dy3+ ions. Energy transfer from Dy3+ to Eu3+ ions in the glasses and the glass-ceramics was confirmed by excitation spectra and luminescence decay kinetics. The average luminescence lifetimes of the Dy3+ emission band at 575 nm under 453 nm excitation decrease with the addition of Eu3+ ions. Energy transfer in the glasses and the glass-ceramics was estimated to be in the range from 11% to 68%, depending on the RE ion concentration.

Sub-10 nm Water-Dispersible β-NaGdF4:X% Eu3+ Nanoparticles with Enhanced Biocompatibility for in Vivo X-ray Luminescence Computed Tomography.

As a novel molecular and functional imaging modality, X-ray luminescence computed tomography (XLCT) has shown its potentials in biomedical and preclinic applications. However, there are still some limitations of X-ray-excited luminescent materials, such as low luminescence efficiency, poor biocompatibility, and cytotoxicity, making in vivo XLCT imaging quite challenging. In this study, for the very first time, we present on using sub-10 nm β-NaGdF4:X% Eu3+ nanoparticles with poly(acrylic acid) (PAA) surface modification, which demonstrate outstanding luminescence efficiency, uniform size distribution, water dispersity, and biosafety, as the luminescent probes for in vivo XLCT application. The pure hexagonal phase (β-) NaGdF4 has been successfully synthesized and characterized by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM), and then the results of X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectrometry (EDX), and elemental mapping further confirm Eu3+ ions doped into NaGdF4 host. Under X-ray excitation, the β-NaGdF4 nanoparticles with a doping level of 15% Eu3+ exhibited the most efficient luminescence intensity. Notably, the doping level of Eu3+ has no effect on the crystal phase and morphology of the NaGdF4-based host. Afterward, β-NaGdF4:15% Eu3+ nanoparticles were modified with PAA to enhance the water dispersity and biocompatibility. The compatibility of in vivo XLCT imaging using such nanoparticles was systematically studied via in vitro cytotoxicity, physical phantom, and in vivo imaging experiments. The ultralow cytotoxicity of PAA-modified nanoparticles, which is confirmed by over 80% cell viability of SH-SY5Y cells when treated by high nanoparticle concentration of 200 μg/mL, overcome the major obstacle for in vivo application. In addition, the high luminescence intensity of PAA-modified nanoparticles enables the location error of in vivo XLCT imaging less than 2 mm, which is comparable to that using commercially available bulk material Y2O3:15% Eu3+. The proposed nanoparticles promote XLCT research into an in vivo stage. Further modification of these nanoparticles with biofunctional molecules could enable the potential of targeting XLCT imaging.

Investigation on the upconversion luminescence in Ho3+/Yb3+ co-doped Ba3Sc4O9 phosphor

A series of Ba3Sc4O9:Ho3+/Yb3+ phosphors were synthesized by a high-temperature solid-state reaction method. The phase purity and upconversion luminescence were characterized by X-ray diffraction and photoluminescence spectroscopy. The sintering temperature and doping concentrations were optimized to obtain the strongest emission intensity. Under 980nm laser diode excitation, the green (545nm, 5F4/5S2→5I8) and red (665nm, 5F5→5I8) emissions were observed. The cross-relaxation and back-energy-transfer processes play an important role to adjust the emission intensity ratio of Green/Red at different dopant concentrations. Based on the energy level diagrams, the energy transfer mechanisms are investigated in detail according to the analysis of pump power dependence and luminescence decay curves. The upconversion luminescence properties of the phosphor were evaluated and the results show good color monochromaticity and relatively high upconversion luminescence intensity. The Ba3Sc4O9:Ho3+/Yb3+ can be a good candidate for green upconversion material in display fields and fluorescent labeling.

High near-infrared transmittance, high intense orange luminescence in vanadium doped indium oxide (V: In2O3) thin films deposited by electron beam evaporation

The V (5wt.%) doped In2O3 (V: In2O3) thin films with the thickness of 50–150nm were deposited on to glass substrate by electron beam evaporation technique and the deposited films were annealed at 200°C in air for 2h. The annealed films were characterized by structural, electrical, optical and photoluminescence properties. X-ray diffraction (XRD) pattern shows that the film is an amorphous nature. The negative sign of the Hall coefficient indicates the n-type conductivity. Experimental results show that the resistivity and transmittance of the films are strongly influenced by film thickness and post deposition annealing. A minimum resistivity of 6.22×10−3Ωcm, a carrier concentration of 5.23×1019cm−3, a Hall mobility of 19.21cm2V−1s−1 and a figure of merit of 1.04×10−4Ω−1 are observed for the film with thickness of 150nm. After annealing the films, the average transmittance is enhanced up to 84% in the near infrared region. The blue-shift of optical band gap is found to increase from 1.62 to 2.25eV with increasing the thickness, whereas the refractive index decreases from 2.92 to 2.64. Structural disorder was observed from the Urbach’s tail. A prominent and high intense orange emission is achieved at room temperature, which may be attributed to oxygen deficiencies or intrinsic defects.

Dynamic monitoring of p53 translocation to mitochondria for the analysis of specific inhibitors using luciferase-fragment complementation.

Intracellular protein translocation plays a pivotal role in regulating complex biological processes, including cell death. The tumor suppressor p53 is a transcription factor activated by DNA damage and oxidative stress that also translocates from the cytosol into the mitochondrial matrix to facilitate necrotic cell death. However, specific inhibitors of p53 mitochondrial translocation are largely unknown. To explore the inhibitors of p53, we developed a bioluminescent probe to monitor p53 translocation from cytosol to mitochondria using luciferase fragment complementation assays. The probe is composed of a novel pair of luciferase fragments, the N-terminus of green click beetle luciferase CBG68 (CBGN) and multiple-complement luciferase fragment (McLuc1). The combination of luciferase fragments showed significant luminescence intensity and high signal-to-background ratio. When the p53 connected with McLuc1 translocates from cytosol into mitochondrial matrix, CBGN in mitochondrial matrix enables to complement with McLuc1, resulting in the restoration of the luminescence. The luminescence intensity was significantly increased under hydrogen peroxide-induced oxidative stress following the complementation of CBGN and McLuc1. Pifithrin-μ, a selective inhibitor of p53 mitochondrial translocation, prevented the mitochondrial translocation of the p53 probe in a concentration-dependent manner. Furthermore, the high luminescence intensity made it easier to visualize the p53 translocation at a single cell level under a bioluminescence microscope. This p53 mitochondrial translocation assay is a new tool for high-throughput screening to identify novel p53 inhibitors, which could be developed as drugs to treat diseases in which necrotic cell death is a major contributor.

Novel CsPbI3 QDs glass with chemical stability and optical properties

Bright and tunable photoluminescence properties for cesium lead halide (CsPbX3) quantum dots (QDs) hinder its application due to their easy degradation in humid and high temperature conditions. Here, we present a simple approach to fabricate a novel CsPbI3 QDs in zinc borosilicate glass through a conventional melting–quenching technique. CsPbI3 QDs glass exhibits high luminescent intensity, tunable narrow-band emission, including the same bandgap energies and emission spectra as CsPbI3 QDs solution, but the quantum yield and decay time show a reduction for the structure defect and electron-hole consist in CsPbI3 QDs glass. Moreover, different heat-treated temperature effect the luminescence of CsPbI3 QDs glass. Absorption and photoluminescence spectra demonstrate that 540°C is the ideal heat-treated temperature for CsPbI3 QDs glass. Consequently, this novel and stable CsPbI3 QDs glass reveals the promising candidate for all-inorganic perovskite in display and solid-state warm lighting source.

Lanthanide Fluorobenzoates as Bio-Probes: a Quest for the Optimal Ligand Fluorination Degree.

The thorough study of fluorinated benzoates of lanthanides (Eu, Tb, Nd, Er, Yb, Gd, La, Lu) is reported. Their composition in single crystal and powder state revealed two predominant structural motifs. An in-depth luminescence study has been performed on the reported fluorobenzoates, showing, that terbium and europium complexes in solid state possess high luminescence intensity with the quantum yield of up to 69 %. High solubility in most organic solvents, as well as in water, combined with the high luminescence intensity in water solution and non-toxicity allowed the testing of europium complexes as bioprobes in cellulo. Among all tested fluorobenzoates, europium 2-fluorobenzoate dihydrate combined the best luminescent properties, thermodynamic stability, aqueous solubility, and non-toxicity, and was shown to be a viable bio-marker.