Doped CaF2 Nanocrystals Research Articles

A membrane biosensor based on colour differences encoded upconversion silica nanoparticles for multiplex nucleic acids detection

Upconversion luminescent nanomaterials provide a powerful tool for multiplex nucleic acids detection simultaneously. However, the conventional encoding methods based on emission spectrum or intensity have limitations due to spectral overlap and cross-relaxation quenching among various activators. Herein, we present a facile method for the preparation of high-capacity upconversion luminescent coding nanoparticles by multiple regulating the synthesis kinetics of lanthanide ions doped CaF2 nanocrystals in mesoporous silica nanotemplets (named C@S). The secondary growth of nanocrystals with different lanthanide ions inside mesopores has a similar performance to that of core/multi-shell-structured upconversion nanoparticles prepared through complicated processes. The textural properties and chemical conformations are maintained after repeated recombination, which is beneficial for reproducible multiplex bioassays. A membrane biosensor is constructed using various probe-modified C@S and a flexible graphene oxide-coated film to detect and identify multiple molecular species in one sample. The colour differences of encoded C@S derived from CIE-L*a*b* colour coordinate system are applied to quantify the divergence of upconversion luminescence for the first time, which allows the upconversion nanoparticles with similar spectra and luminescence colours to be used in the same multiplex detection platform and avoids subjective judgement. This work opens new opportunities for upconversion luminescent materials in the field of automatic high-throughput detection.

Lanthanide-doped upconversion glass–ceramic photocatalyst fabricated from fluorine-containing waste for the degradation of organic pollutants

Fluorine-containing waste is one kind of hazardous waste characteristic by hard disposal and utilization, it is an attractive way to prepare for fluoride-based luminescent matrix. In this work, to realize the high value-added utilization of fluorine-containing waste and reduce cost of the raw materials for preparation near-infrared (NIR) glass–ceramic (GC) photocatalyst, the pure fluoride of luminescent matrix was replaced by introducing fluorine-containing waste. The waste contained NIR GC photocatalyst was synthesis by the method of facile in-situ etching of an upconversion GC with HCl, which possesses core–shell structure, where the GC micro-powder including optically active centers lanthanides doped CaF2 nanocrystals are displayed as the core, and the BiOCl is as the superficial coating. The upconversion emission performance of CaF2 based luminescent matrix in photocatalyst is not weakened with HCl etching. NIR GC photocatalyst has high methyl orange and enrofloxacin degradation rate of 86 % and 82 % over 180 min after NIR light irradiation, respectively. The UV–Vis–NIR photocatalytic activity was enhanced degradation rate (93 % in 15 min) of enrofloxacin compared with those of commercial P25 and BiOCl. In addition, the photocatalyst had stable photocatalytic activity and it also can be regenerated. The study provided references for high value-added utilization fluorine-containing waste.

Europium (II)-Doped CaF2 Nanocrystals in Sol-Gel Derived Glass-Ceramic: Luminescence and EPR Spectroscopy Investigations.

The remarkable properties of Eu2+-activated phosphors, related to the broad and intense luminescence of Eu2+ ions, showed a high potential for a wide range of optical-related applications. Oxy-fluoride glass-ceramic containing Europium (II)-doped CaF2 nanocrystals embedded in silica matrix were produced in two steps: glass-ceramization in air at 800° with Eu3+-doped CaF2 nanocrystals embedded followed by Eu3+ to Eu2+ reduction during annealing in reducing atmosphere. The broad, blue luminescence band at 425 nm and with the long, weak tail in the visible range is assigned to the d → f type transition of the Eu2+ located inside the CaF2 nanocrystals in substitutional and perturbed sites, respectively; the photoluminescence quantum yield was about 0.76. The X-ray photoelectron spectroscopy and Electron paramagnetic spectroscopy confirmed the presence of Eu2+ inside the CaF2 nanocrystals. Thermoluminescence curves recorded after X-ray irradiation of un-doped and Eu2+-doped glass-ceramics showed a single dominant glow peak at 85 °C related to the recombination between F centers and Eu2+ related hole within the CaF2 nanocrystals. The applicability of the procedure can be tested to obtain an oxy-fluoride glass-ceramic doped with other divalent ions such as Sm2+, Yb2+, as nanophosphors for radiation detector or photonics-related applications.

Luminescence and photoionization of X-ray generated Sm2+ in coprecipitated CaF2 nanocrystals.

We report photoluminescence and photoionization properties of Sm2+ ions generated by X-irradiation of nanocrystalline CaF2:Sm3+ prepared by coprecipitation. The nanocrystals were of 46 nm average crystallite size with a distribution of ±20 nm and they were characterised by XRD, TEM and SEM-EDS. At room temperature, the X-irradiated sample displayed broad electric dipole allowed Sm2+ 4f55d (A1u) → 4f6 7F1 (T1g) luminescence at 725 nm that narrowed to an intense peak at 708 nm on cooling to ∼30 K. The narrow f-f transitions of Sm3+ were also observed. The X-irradiation-induced reduction of Sm3+ + e- → Sm2+ as a function of X-ray dose was investigated over a very wide dynamic range from 0.01 mGy to 850 Gy by monitoring the photoluminescence intensities of both Sm2+ and Sm3+ ions. The reverse Sm2+ → Sm3+ + e- photoionization can be modelled by employing dispersive first-order kinetics and using a standard gamma distribution function, yielding an average separation of 13 Å between the Sm2+ ions and the hole traps (e.g. oxide ion impurities). The present results point towards potential applications of Sm doped CaF2 nanocrystals in the fields of dosimetry and X-ray imaging.

Synthesis of an efficient lanthanide doped glass-ceramic based near-infrared photocatalyst by a completely waterless solid-state reaction method.

A novel efficient near-infrared photocatalyst of oxyfluoride glass-ceramic (Er3+/Yb3+-CaO-Al2O3-SiO2-CaF2)/TiO2 was synthesized by a simple solid-state reaction method, with optically active center (Er3+/Yb3+) doped CaF2 nanocrystals in glass-ceramic micro powders and nanosized anatase TiO2 as the superficial coating. This near-infrared photocatalyst preparation method has a high production efficiency with no wastewater generated.

Structure and optical properties of transparent Er3+-doped CaF2–silica glass ceramic prepared by controllable sol–gel method

Transparent Er3+-doped CaF2–silica glass ceramics were prepared by the direct physical introduction of Er3+ doped CaF2 nanocrystals into acid-catalyzed sol–gel silica glass. The physical methods of ball milling, ultrasonic baths, and stirring were investigated to disperse Er3+ doped CaF2 nanocrystals in the silica sols. The CaF2–silica sol mixture went through gelation and heat-treatment to form Er3+-doped CaF2–silica glass ceramics. The morphology of Er3+ doped CaF2 in silica glass did not change after heat-treatment at 600°C for 10h. The experimental results showed that Er3+ doped CaF2 in the glass ceramic prepared with the assistance of ball milling possesses the best dispersity and homogeneity. The highest in-line transmittance of the glass ceramic reached up to 85% in visible region. Glass ceramic exhibits efficient up-conversion emissions corresponding to the Er3+:4F9/2→4I15/2 transition and long lifetime of 4F9/2 level (1.73ms) under 980nm excitation.

Ce3+ sensitized bright white light emission from colloidal Ln3+ doped CaF2 nanocrystals for the development of transparent nanocomposites

Intense white light emissions are observed from colloidal single component Ce3+/Ce3+/Ce3+/Ce3+-doped CaF2 nanocrystals and their transparent nanocomposites.

Morphology and photoluminescence properties of Er3+-doped CaF2 nanocrystals patterned by laser irradiation in oxyfluoride glasses

Lines with Er3+-doped CaF2 nanocrystals were patterned by laser irradiations in aluminoborosilicate-based oxyfluoride glasses. The morphology and dispersion state of CaF2 nanocrystals were examined from transmission electron microscope (TEM) observations combined with focused ion beam sample preparations. The size of CaF2 nanocrystals present in the region close to the center of lines was larger than that in the region close to the edge of lines. Micro-photoluminescence (PL) spectra for the line part showed clear emissions corresponding to the f–f transitions of Er3+ ions, and the correlation between the morphology and dispersion state of CaF2 nanocrystals and PL properties (intensity and degree of the Stark splitting) of Er3+ ions incorporated into in CaF2 nanocrystals was clarified. The formation mechanism of CaF2 nanocrystals in the laser irradiated part was discussed from the temperature distribution model.

Spectroscopic ellipsometry investigations of Eu-doped oxy-fluoride glass and glass-ceramics

Oxyfluoride glass-ceramics in the system SiO2–Al2O3–CaF2–EuF3 containing Eu3+-doped CaF2 nanocrystals were produced by using controlled crystallization of melt-quenched glass. X-ray diffraction and scanning electron microscopy data have revealed the formation of CaF2 nanocrystals of about 50nm size. The Eu3+-dopant ions act as the nucleating agent necessary to initiate the crystallization process. The refractive index is higher in the glass ceramics than in the initial glass and varies as the annealing time increases. Two competitive processes are responsible for this behavior, the crystallization of the CaF2 phase and the decrease of the glass ceramic mass density.

Morphology and optical properties of Mg and Sr doped CaF2 nanocrystals

Magnesium (Mg) and Strontium (Sr) doped Calcium fluoride nanocrystals were synthesized by co-precipitation method. The cubic structure of the samples was confirmed by Powder X-ray diffraction. The average crystallite size of Mg doped samples was found to be ~25nm whereas in Sr doped one it was ~35nm. The morphological features revealed that the nanocrystals were agglomerated, crispy and porous. The as-prepared samples showed the presence of hydroxyl groups. The optical absorption spectrum of as-prepared Mg doped samples showed a strong absorption band peaked at ~233nm whereas the Sr doped one showed a prominent absorption peak at 248nm. A strong PL emission was observed at ~300nm in Mg doped samples. However, the Sr doped samples showed two prominent emissions at ~345 and 615nm.

New transparent glass–ceramics containing large grain Eu3 +:CaF2 nanocrystals

Transparent glass–ceramics containing Eu3+ doped CaF2 nanocrystals were prepared. The microstructural evolution of the samples was studied with DTA, X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). After heat-treatment at 560°C for 10h, the precipitated CaF2 crystallites in the sample were 60–90nm in size and dispersed equally in the amorphous phase. The high transparency of glass–ceramics was mainly ascribed to the small difference of refractivity index between CaF2 and the parent glass (⊿nD≈0.05). The luminescent properties of parent glass and glass–ceramics were also estimated to confirm the incorporation of Eu3+ into the precipitated CaF2 phase.

Nanoparticles size effects in thermoluminescence of oxyfluoride glass-ceramics containing Sm3+-doped CaF2 nanocrystals

Oxyfluoride glass-ceramic in the system SiO2–Al2O3–CaF2–SmF3 containing Sm3+-doped CaF2 nanocrystals in the range from 15 to 150 nm size were produced by using the controlled ceramization of the precursor glass. The incorporation of the Sm3+-dopant ion in the glass ceramic creates new electron-trapping centers and thermoluminescence (TL) method has been used in order to trace their evolution during glass ceramization. The 370 °C TL peak observed in precursor glass has been assigned to the recombination of the electrons released from the Sm2+-traps in the amorphous glass network. In the glass-ceramic sample containing nanocrystals with about 15 nm size the new weak TL peaks at 270, 290, and 310 °C were attributed to the recombination of the electrons released from the Sm2+-traps located mainly at the surface of the CaF2 nanocrystals. In the glass-ceramic sample containing nanocrystals with about 150 nm size, the new TL peaks at 232, 270, and 302 °C size have been assigned to the recombination of the electrons released from the Sm2+-traps located inside the CaF2 nanocrystals.

Two‐Dimensional Mapping of Er3+ Photoluminescence in CaF2 Crystal Lines Patterned by Lasers in Oxyfluoride Glass

The laser‐induced crystallization method is applied to an oxyfluoride glass with the composition of 41.5SiO2–21.3Al2O3–4.8CaO–12.6NaF–16.4CaF2–2.9NiO–0.5ErF3 (mol%), and the lines consisting of CaF2 nanocrystals (diameter: ∼20 nm) are patterned on the glass surface. It is found from micro‐photoluminescence (PL) spectra of Er3+ ions that Er3+ ions are incorporated into CaF2 nanocrystals formed by laser (continuous‐wave Yb:YVO4 fiber laser with a wavelength of 1080 nm) irradiations. Two‐dimensional mappings of the PL intensity for the 4S3/2→4I15/2 transition of Er3+ ions are measured for the surface and cross section of the patterned lines. It is found that two phases giving different PL intensities are formed in the laser‐irradiated region, suggesting that the center part of the laser‐irradiated region consists of Er3+‐doped CaF2 nanocrystals and the surrounding of the center part gives the fluoride ion rich coordination state for Er3+ ions. The formation mechanism of Er3+‐doped CaF2 nanocrystals is related to the temperature distribution of the laser‐irradiated region.

Optical spectroscopy and confocal fluorescence imaging of upconverting Er3+-doped CaF2 nanocrystals

Up-conversion emission and confocal fluorescence imaging of Er3+-doped CaF2 nanocrystals were investigated using infrared excitation. At Er3+ concentrations less than 2.8mol%, green emission was dominant while red prevailed at higher concentrations. The simultaneous green and red emission and change in relative intensities is explained with a mechanism utilizing concepts of TPA, ESA, ET, and CR processes.