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

Infrared Photoluminescence of Nd-Doped Sesquioxide and Fluoride Nanocrystals: A Comparative Study

Lanthanide ions possess various emission channels in the near-infrared region that are well known in bulk crystals but are far less studied in samples with nanometric size. In this work, we present the infrared spectroscopic characterization of various Nd-doped fluoride and sesquioxide nanocrystals, namely Nd:Y2O3, Nd:Lu2O3, Nd:Sc2O3, Nd:YF3, and Nd:LuF3. Emissions from the three main emission bands in the near-infrared region have been observed and the emission cross-sections have been calculated. Moreover, another decay channel at around 2 μm has been observed and ascribed to the 4F3/2→4I15/2 transition. The lifetime of the 4F3/2 level has been measured under LED pumping. Emission cross-sections for the various compounds are calculated in the 1 μm, 900 nm, and 1.3 μm regions and are of the order of 10−20 cm2 in agreement with the literature results. Those in the 2 μm region are of the order of 10−21 cm2.

Tailoring defect structure and dopant composition and the generation of various color characteristics in Eu3+ and Tb3+ doped MgF2 phosphors

A novel approach to generate a wide range of color characteristics such as near white, yellow, orange and red in MgF₂, by proper tailoring of the defect structure and varying the composition of Eu³⁺ and Tb³⁺ dopant ions have been presented here. It has been observed from positron annihilation lifetime spectroscopy (PALS) study that various defect centers such as mono vacancies and their cluster forms exist in the system, whose amount varies upon varying the dopant ion's composition. The experimentally observed positron lifetime values of the defect centers also matched well with the theoretically calculated lifetime values using the MIKA-DOPPLER package. It has been found that a few vacancies or defect centers act as color centers, while the cluster vacancies change the local symmetry of the rare earth ion by inducing more distortion surrounding them thereby resulting in different emission characteristics in the photoluminescence (PL) study. The defect-related host emission in combination with the green and red emission from Tb³⁺ and Eu³⁺ ions generated near-white-light in some of the compounds, while other compounds showed a variety of other color characteristics due to the Tb³⁺ → Eu³⁺energy transfer dynamics. The various defect-related emissions, the role of the defect-related trap state in the decay kinetics and the energy-transfer dynamics were also understood by analyzing the electronic structure using HSE06 hybrid functional calculation.

Unraveling the site-specific energy transfer driven tunable emission characteristics of Eu3+ & Tb3+ co-doped Ca10(PO4)6F2 phosphors

In this study we have explored Ca₁₀(PO₄)₆F₂ as host to develop a variety of phosphor materials with tunable emission and lifetime characteristics based on Eu³⁺ and Tb³⁺ as co-dopant ions and the energy transfer process involved with them. The energy transfer from the excited state of Tb³⁺ ion to the ⁵D₀ state of Eu³⁺ makes it possible to tune the colour characteristics from yellow to orange to red. Further, such energy transfer process is highly dependent on the concentration of Eu³⁺ and Tb³⁺ ions and their site-selective distribution among the two different Ca-sites (CaO₉ and CaO₆F) available. We have carried out DFT based theoretical calculation for both Eu³⁺ and Tb³⁺ ions in order to understand their distribution. It was observed that in cases of co-doped sample, Tb³⁺ ions prefer to occupy the Ca2 site in the CaO₆F network while Eu³⁺ ions prefer Ca1 site in the CaO₉ network. This distribution has significant impact on the lifetime values and the energy transfer process as observed in the experimental photoluminescence lifetime values. We have observed that for the 1^st series of compounds, wherein the concentration Tb³⁺ ions are fixed, the energy transfer from Tb³⁺ ion at Ca2 site to Eu³⁺ ion at Ca1 site is dominating (Tb³⁺@Ca2 → Eu³⁺@Ca1). However, for the 2^nd series of compounds, wherein the concentration Eu³⁺ ions are fixed, the energy transfer process was found to occur from the excited Tb³⁺ ion at Ca1 site to Eu³⁺ ions at both Ca1 and Ca2 (Tb³⁺@Ca1 → Eu³⁺@Ca1 and Tb³⁺@Ca1 → Eu³⁺@Ca2). This is the first reports of its kind on site-specific energy transfer driven colour tunable emission characteristics in Eu³⁺ and Tb³⁺ co-doped Ca₁₀(PO₄)₆F₂ phosphor and it will pave the way for the future development of effective colour tunable phosphor materials based on a single host and same co-dopant ions.

Various site specific energy transfer (ET) process such as Tb³⁺@Ca2 → Eu³⁺@Ca1, Tb³⁺@Ca1 → Eu³⁺@Ca2 and Tb³⁺@Ca1 → Eu³⁺@Ca1 were explored in Eu³⁺ and Tb³⁺ co-doped Ca₁₀(PO₄)₆F₂ phosphor, which are responsible for tunable colour characteristics.

Enhancing the static green up-conversion luminescence of NaY(MoO4)2:Yb/Er microcrystals via an annealing strategy for anti-counterfeiting applications

The majority of the fabrication procedures of lanthanide-doped materials involve thermal treatment that often results in crystallite regrowth, stabilizing the specific crystal structure and resulting in luminescence enhancement. The efficiency and intensity of up-conversion luminescence are closely related to the structure and synthesis process of the materials. Herein, well-crystallized and pure tetragonal NaY(MoO4)2 microcrystals with a uniform octahedral shape have been successfully synthesized via an environmentally friendly hydrothermal method, followed by annealing treatment. The phases, structures, morphologies, and compositions of the synthesized products annealed at 500-1000 °C remain unchanged, indicating high thermal stability. Furthermore, the NaY(MoO4)2:Yb3+/Er3+ microcrystals exhibit strong green emission when irradiated using infrared (980 nm) or ultraviolet (378 nm) wavelengths. Upon 980 nm excitation, up to 37-fold luminescence enhancement is achieved when the samples are annealed at about 700 °C. Interestingly, the high colour purity of the strong green emission is not only independent of the dopant concentration and heat treatment temperature, but it is also independent of the excitation conditions, including power and wavelength, and this makes it particularly suitable as a green safety signal light and luminescent security ink in paintings. As-prepared safety inks with NaY(MoO4)2:Yb3+/Er3+ microcrystals were used for visual fingerprint recognition printed on A4 paper with three-level fingerprint security features, significantly increasing the difficulty of illegal imitation and enhancing the levels of anti-counterfeiting.

Lanthanide ion-doped silica nanohelix: a helical inorganic network acts as a chiral source for metal ions

We demonstrate that lanthanide ions doped in nanometrical silica helices with a chirally arranged siloxane network without any organic mediates show induced chiroptical properties such as circular dichroism and circularly polarized luminescence.

Multimodal PSSMA-Functionalized GdF3 : Eu3+ (Tb3+ ) Nanoparticles for Luminescence Imaging, MRI, and X-Ray Computed Tomography

Biocompatible poly(4-styrenesulfonic acid-co-maleic acid)-stabilized GdF₃  : Eu³⁺ (Tb³⁺ ) nanoparticles were obtained by a one-step coprecipitation method in ethylene glycol or water. The particles are very small (3 nm), have a narrow size distribution, and were detectable by fluorescence, magnetic resonance, and X-ray contrast imaging. These properties allow multimodal imaging, which has prospective applications in the simultaneous and detailed detection of diseased tissues.

Rapid and quantitative detection of urinary Cyfra21-1 using fluorescent nanosphere-based immunochromatographic test strip for diagnosis and prognostic monitoring of bladder cancer

Bladder cancer is a common malignant tumour with high recurrence rate. Cytokeratin 19 fragments (Cyfra21-1) in urine has been regarded as a promising biomarker for the prognosis and diagnosis of bladder cancer due to the relevance of its high urinary level to the bladder cancer patients. However, currently detection methods of Cyfra21-1 have their limits, such as complicated steps, limited sensitivity or unsatisfying specificity. In this study, we developed a novel time-resolved fluoroimmuno test strip by using europium chelate microparticle (Eu-CM). Detection was performed in simple steps by carrying drops of sample into the well of the test strip, waiting for 15 min and inserting the strip into a fluorescence strip reader for quantitation. The standard curve equation of the test strip was y = 0.0177x + 0.01 (R² = .9993). In the analysis of human urine samples (n = 115), it demonstrated a good performance (accuracy: CV < 10%, AUC: 0.989). With the cut-off value of 81 ng/mL, the sensitivity and specificity for bladder cancer were 92.86 and 100%, respectively. In comparison to ELISA and electrochemiluminescence methods, the Eu-CM based time-resolved fluoroimmuno test strip provided a rapid, sensitive and reliable method for monitoring bladder cancer. It may be applied as a non-invasive approach for in point-of-care for bladder cancer detection.

Synthesis, functionalization and properties of uniform europium-doped sodium lanthanum tungstate and molybdate (NaLa(XO4)2, X = Mo,W) probes for luminescent and X-ray computed tomography bioimaging

A one-pot simple procedure for the synthesis of uniform, ellipsoidal Eu³⁺-doped sodium lanthanum tungstate and molybdate (NaLa(XO₄)₂, X  = W, Mo) nanophosphors, functionalized with carboxylate groups, is described. The method is based on a homogeneous precipitation process at 120 °C from appropriate Na⁺, Ln³⁺ and tungstate or molybdate precursors dissolved in ethylene glycol/water mixtures containing polyacrylic acid. A comparative study of the luminescent properties of both luminescent materials as a function of the Eu³⁺ doping level has been performed to find the optimum nanophosphor, whose efficiency as X-ray computed tomography contrast agent is also evaluated and compared with that of a commercial probe. Finally, the cell viability and colloidal stability in physiological pH medium of the optimum samples have also been studied to assess their suitability for biomedical applications.

Polyvinylpyrrolidone Nanofibers Encapsulating an Anhydrous Preparation of Fluorescent SiO₂⁻Tb3+ Nanoparticles

A novel anhydrous preparation of silica (SiO₂)-encapsulated terbium (Tb³⁺) complex nanoparticles has been investigated. The SiO₂-Tb³⁺ nanoparticles are incorporated in electrospun polyvinylpyrrolidone hybrid nanofibers. Transmission electron microscopy confirms that Tb³⁺ complexes are uniformly and stably encapsulated in or carried by nanosilica. The influence of pH on the fluorescence of Tb³⁺ complexes is discussed. The properties, composition, structure, and luminescence of the resulting SiO₂⁻Tb³⁺ hybrid nanoparticles are investigated in detail. There is an increase in the fluorescence lifetime of SiO₂⁻Tb³⁺ nanoparticles and SiO₂⁻Tb³⁺/polyvinylpyrrolidone (PVP) hybrid nanofibers compared with the pure Tb³⁺ complexes. Due to the enhanced optical properties, the fluorescent hybrid nanofibers have potential applications as photonic and photoluminescent materials.

Synthesis and Rational design of Europium and Lithium Doped Sodium Zinc Molybdate with Red Emission for Optical Imaging

Highly efficient fluorescent and biocompatible europium doped sodium zinc molybdate (NZMOE) nanoprobes were successfully synthesized via Polyol method. Non-radiative defect centres get reduced with Li+ co-doping in NZMOE nanoprobes. XRD spectra and Rietveld refinement confirmed successful incorporation of lithium ion and crystallinity was also improved with Li+ co-doping. The shape of phosphor is rod shaped, as determined by TEM. Significant enhancement in photoluminescence intensity was observed with 266, 395 and 465 nm excitations. Profound red emission was recorded for 5 at% Li+ co-doped NZMOE nanoprobes with 266 nm excitation. It shows high asymmetry ratio (~15), color purity (94.90%) and good quantum efficiency (~70%). Judd Ofelt parameters have been calculated to measure intensity parameters and radiative transition rates. In order to measure biocompatibility of the nanoprobes, cytotoxicity assays were performed with HePG2 cells. The fluorescence emitted from phosphor material treated HePG2 cells was also measured by Laser Scanning Confocal Microscopy. The bright red fluorescence in HePG2 cells treated with very low concentration (20 μg/ml) of phosphor material indicates that it could be a promising phosphor for biological detection or bio-imaging.

Lifetime-Encoded Infrared-Emitting Nanoparticles for in Vivo Multiplexed Imaging

Advanced diagnostic procedures are required to satisfy the continuously increasing demands of modern biomedicine while also addressing the need for cost reduction in public health systems. The development of infrared luminescence-based techniques for in vivo imaging as reliable alternatives to traditional imaging enables applications with simpler and more cost-effective apparatus. To further improve the information provided by in vivo luminescence images, the design and fabrication of enhanced infrared-luminescent contrast agents is required. In this work, we demonstrate how simple dopant engineering can lead to infrared-emitting rare-earth-doped nanoparticles with tunable (0.1-1.5 ms) and medium-independent luminescence lifetimes. The combination of these tunable nanostructures with time-gated infrared imaging and time domain analysis is employed to obtain multiplexed in vivo images that are used for complex biodistribution studies.

Enhanced red luminescence and improved crystallinity in NaEu(WO4)2 phosphors: an electron beam irradiation study

Band gap engineering in NaEu(WO₄)₂ red phospors via dose-dependent EB irradiation: a new strategy for improving fluorescence intensity.

NaGd(MoO4)2 nanocrystals with diverse morphologies: controlled synthesis, growth mechanism, photoluminescence and thermometric properties

Pure tetragonal phase, uniform and well-crystallized sodium gadolinium molybdate (NaGd(MoO4)2) nanocrystals with diverse morphologies, e.g. nanocylinders, nanocubes and square nanoplates have been selectively synthesized via oleic acid-mediated hydrothermal method. The phase, structure, morphology and composition of the as-synthesized products are studied. Contents of both sodium molybdate and oleic acid of the precursor solutions are found to affect the morphologies of the products significantly, and oleic acid plays a key role in the morphology-controlled synthesis of NaGd(MoO4)2 nanocrystals with diverse morphologies. Growth mechanism of NaGd(MoO4)2 nanocrystals is proposed based on time-dependent morphology evolution and X-ray diffraction analysis. Morphology-dependent down-shifting photoluminescence properties of NaGd(MoO4)2: Eu(3+) nanocrystals, and upconversion photoluminescence properties of NaGd(MoO4)2: Yb(3+)/Er(3+) and Yb(3+)/Tm(3+) nanoplates are investigated in detail. Charge transfer band in the down-shifting excitation spectra shows a slight blue-shift, and the luminescence intensities and lifetimes of Eu(3+) are decreased gradually with the morphology of the nanocrystals varying from nanocubes to thin square nanoplates. Upconversion energy transfer mechanisms of NaGd(MoO4)2: Yb(3+)/Er(3+), Yb(3+)/Tm(3+) nanoplates are proposed based on the energy level scheme and power dependence of upconversion emissions. Thermometric properties of NaGd(MoO4)2: Yb(3+)/Er(3+) nanoplates are investigated, and the maximum sensitivity is determined to be 0.01333 K(-1) at 285 K.

Luminescence and luminescence quenching of highly efficient Y2Mo4O15:Eu(3+) phosphors and ceramics

A good LED phosphor must possess strong enough absorption, high quantum yields, colour purity, and quenching temperatures. Our synthesized Y₂Mo₄O₁₅:Eu³⁺ phosphors possess all of these properties. Excitation of these materials with near-UV or blue radiation yields bright red emission and the colour coordinates are relatively stable upon temperature increase. Furthermore, samples doped with 50% Eu³⁺ showed quantum yields up to 85%, what is suitable for commercial application. Temperature dependent emission spectra revealed that heavily Eu³⁺ doped phosphors possess stable emission up to 400 K and lose half of the efficiency only at 515 K. In addition, ceramic disks of Y₂Mo₄O₁₅:75%Eu³⁺ phosphor with thickness of 0.71 and 0.98 mm were prepared and it turned out that they efficiently convert radiation of 375 and 400 nm LEDs to the red light, whereas combination with 455 nm LED yields purple colour.