YPO4 Nanocrystals Research Articles

In Situ Crystallization of SiO Spherical Nanocrystals in Optical Fibers

Extreme synthesis conditions can lead to discover materials and phenomena that are unknown under standard synthesis laboratory conditions. The particularities of the optical fiber fabrication, such as extreme temperatures, quenching heat treatments and the pressure generated during fiber drawing, among others, can be leveraged to explore novel phenomena at the nanoscale when optical fibers are engineered by nanoparticle doping. In this work, we demonstrate that starting from tetragonal cubic-shaped YPO4 nanocrystals contained into a silica-based optical fiber core, with a silica-based glass composition slightly modified with Ge P, and Al, it is possible to nucleate isolated spherical-shaped SiO nanocrystals by controlling fiber drawing temperature. This work demonstrates the existence of crystalline SiO, discussing the possible formation mechanism in detail, which addes new knowledge to silicon oxide family. Moreover, we show the suitability of using SiO nanocrystals for fabricating Rayleigh scattering enhanced optical fibers that can be applied for distributed sensing applications.

Towards REPO4 nanocrystal-doped optical fibers for distributed sensing applications

Rayleigh scattering enhanced nanoparticle-doped optical fibers, for distributed sensing applications, is a new technology that offers unique advantages to optical fiber community. However, the existing fabrication technology, based on in situ grown alkaline earth nanoparticles, is restricted to few compositions and exhibit a great dependence on many experimental conditions. Moreover, there is still several uncertainties about the effect of drawing process on the nanoparticle characteristics and its influence on the scattering enhancement and the induced optical loss. In this work, we shed light on all these issues that prevent the progress in the field and demonstrate the suitability of doping optical fibers with YPO4 nanocrystals for developing tunable Rayleigh scattering enhanced nanoparticle-doped optical fibers. An exhaustive 3D microstructural study reveals that their features are closely linked to the fiber drawing process, which allow the size and shape engineering at the nanoscale. In particular, the YPO4 nanocrystals preserve their features to a large extent when the optical fibers are drawn below 1950 °C, which allows obtaining homogeneous nanocrystal features and optical performance. Fabricated fibers exhibit a tunable enhanced backscattering in the range of 15.3–54.3 dB, with respect to a SMF-28 fiber, and two-way optical losses in the range 0.3–160.7 dB/m, revealed by Optical Backscatter Reflectometry (OBR) measurements. This allows sensing lengths from 0.3 m up to more than 58 m. The present work suggests a bright future of YPO4 nanocrystals for distributed sensing field and open a new gate towards the incorporation of other rare-earth orthophosphate (REPO4) nanocrystals with pre-defined characteristics that will overcome the limitations of the current in situ grown alkaline earth-based technology.

Unveiling Structural Insights into Nanocrystal-Doped Optical Fibers via Confocal Raman Microscopy.

An in-depth characterization of nanoparticle-doped optical fibers is crucial to understand the potential new functionalities of the engineered glass and thus their applicability fields. The high temperatures of the manufacturing process strongly affect the nanoparticle features, and therefore, their analysis is necessary after fiber drawing. However, the difficulties associated with the use of atomic resolution microscopies to analyze the nanoparticle features in the fiber core, mainly related to sample preparation and expensive costs, usually prevent their study. In this work, we overcome some of those limitations and demonstrate, for the first time, the suitability of structurally and microstructurally studying in detail nanocrystals contained in a fiber core of ∼10 μm by combining confocal Raman microscopy, Rayleigh light-scattering microscopy, and scanning electron microscopy (SEM). A thorough study of cubic-shaped and rod-shaped YPO4 nanocrystals contained in optical fibers reveals their crystallization in tetragonal (t) and monoclinic (m) structures, respectively. The symmetric (ν1) and asymmetric stretching (ν3) Raman modes display a different and remarkable red shift as particle size decreases in both types of nanocrystals, which in the case of the cubic-shaped nanocrystals is fitted to an exponential function along with a Raman peak broadening. Moreover, their Raman dependence vs temperature is evaluated up to 600 °C, observing a phonon softening that follows a linear behavior, which is discussed in detail. These findings add new insights to pure m-YPO4, which was unknown to date, and the REPO4 family and open up new avenues that can be extrapolated to other nanostructures incorporated into optical fiber cores, which will advance progress in the field of nanoparticle-doped optical fibers.

Hydrothermal synthesis and tunable luminescence of YPO4:Eu2+/Eu3+, Tb3+ nanocrystals

The homogeneous and well crystallized rare earth ions RE3+ (RE = Eu, Tb) doped YPO4 and YPO4·0.8H2O nanocrystals (NCs) are synthesized by a simple hydrothermal route. The samples are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectroscopy. The results indicate that the pH value of precursor affects the phase composition and surface morphology of the final product. The results of XPS indicate that both Eu2+ and Eu3+ co-exist in YPO4 NCs, implying that the self-reduction from Eu3+ to Eu2+ takes place with the absence of reducing agents, charge compensation reagents and charge carrier trapping processes. In addition, YPO4:Eu and YPO4·0.8H2O:Eu samples exhibit strong and bright blue and red emission. According to PL spectroscopy, the blue emission is originated from host lattice and Eu2+ ion luminescence and red emission from Eu3+. YPO4:Tb, Eu samples can be effectively excited at 355 nm. An energy transfer phenomenon appears between Tb3+ and Eu3+. It is interesting that by changing the concentration of Tb3+, white phosphor from Y0.90PO4:0.04 Tb, 0.06Eu NCs are successfully obtained. Moreover, the Y0.90PO4:0.04 Tb, 0.06Eu has excellent thermal stability. These results indicate that the combination of defect and rare earth luminescence in YPO4:Tb, Eu NCs can produce tunable luminescence color, which may have potential applications in fields such as solid-state lighting and field emission displays.

Cubic-Shaped and Rod-Shaped YPO4 Nanocrystal-Doped Optical Fibers: Implications for Next Generation of Fiber Lasers

Engineering silica optical fibers by nanoparticle doping is a promising technology that allows the introduction of new functionalities and extends their applicable fields. However, the knowledge gap about the impact of the extreme fabrication temperatures on the nanoparticle features prevents field progress. Herein, we demonstrate that the particularities of fiber fabrication, such as fast-heating rates and quenching heat treatments, can be leveraged to explore unlikely phenomena at the nanoscale under standard laboratory conditions. Tetragonal cubic-shaped and monoclinic rod-shaped YPO4 nanocrystals are in situ nucleated in a silica-based fiber core glass, slightly modified with Ge and P, which shows for the first time, the possibility of doping optical fibers with this type of nanostructures, in terms of shape, composition, and structure of the nanocrystals. Structural and anisotropic differences allow engineering differently their shape and composition in the fiber core by tailoring the drawing temperature, as revealed by a thorough study consisting of scanning electron microscopy (SEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), electron energy loss spectroscopy (EELS), and high-resolution transmission electron microscopy (HRTEM). This work demonstrates, for the first time, the possibility of doping optical fibers fabricated by modified chemical vapor deposition (MCVD) with anisotropic nanostructures, as well as the stability of the monoclinic YPO4 phase. These findings open up new avenues to study shape-dependent properties of rare-earth orthophosphate (REPO4) nanostructures in optical fibers which will allow incorporating unprecedented functionalities and will have an impact in several fields of application, such as fiber lasers and optical fiber amplifiers, among others.

Thermally-induced structural phase transition in rare earth orthophosphate nanocrystals for highly sensitive thermal history paints

It was demonstrated that he temperature-driven irreversible structural phase transformations in the Eu3+ activated LaPO4, La0.5Y0.5PO4, and YPO4 nanocrystals can be used for the thermal history measurements over the 200oC-1000oC temperature range. Increase of the temperature caused significant changes in the Eu3+ local surroundings and, in consequence modified the intensity and the emission spectra. We showed that the intensity ratio of Eu3+ 5D0→ 7F2 to 5D0→7F1 emissions may serve as a highly-sensitive indicator of the highest temperature to which the nanocrystals were exposed to. The relative sensitivity of Y0.5La0.5PO4:2 %Eu3+ based thermal history paint was as high as 0.8 %/°C at 1000 °C. The thermal history surface map of the square steel plate covered with Y0.5La0.5PO4:2 %Eu3+ paint, heated locally at one of the corner is obtained as proof-of-concept experiment. The proposed ratiometric readout strategy facilitates measurement and enhances the accuracy of thermal history analysis.

Tunable luminescence between Stark levels of Pr3+:YPO4 nanocrystals by different crystal phase

We report time-resolved second-order fluorescence between Stark levels of 1D2 and 3H4 in Pr3+:YPO4 nanocrystals with different crystal phase. Both intensity ratios of transition peaks between Stark levels and fluorescence lifetimes are modulated by phase composition and dressing effect. We have found that the maximum excitation peak shifts from yellow to orange-red region with continuous phase transformation from hexagonal phase to tetragonal phase, which is attributed to different multi-phonon relaxation rate induced by O–H group in hexagonal phase. The fluorescence lifetimes and intensity ratios of splitting peaks in time domain have also been effectively modulated by choosing excitation frequencies to resonate with different Stark levels. Both wavelength and time tunable luminescence has potential applications in biological labeling, imaging and solid state display devices.

Approaches to contactless optical thermometer in the NIR spectral range based on Nd3+ doped crystalline nanoparticles

The fluorescence kinetics and spectral intensity ratio (FIR) methods for contactless optical temperature measurement in the NIR spectral range with Nd3+ doped YAG micro- and YPO4 nanocrystals are considered and the problems are revealed. The requirements for good temperature RE doped crystalline nanoparticles sensor are formulated.

White Light Emission Characteristics of Tb3+/Sm3+ Co-Doped Glass Ceramics Containing YPO4 Nanocrystals

The Tb3+/Sm3+ single-doped and co-doped glasses and glass ceramics containing YPO4 nanocrystals have been synthesized by melt quenching method. The structural and luminescent properties of these glass specimens were investigated. Under 375 nm wavelength excitation, the emission spectra combined with blue, green and red bands were observed, which achieved the white light emission. Moreover, the energy transfer between Tb3+ and Sm3+ ions was validated by decay lifetime measurement and energy level diagram. The color coordinates (x = 0.333, y = 0.333), correlated color temperature (5595 K) and the color rendering index (Ra=80.5) indicated that the glass ceramics were considered to be good lighting source. Hence, the YPO4-based Tb3+/Sm3+ co-doped glass ceramics can act as potential matrix materials for white light-emitting diodes under ultraviolet excitation.

Luminescent properties of Ce3+/Tb3+co-doped glass ceramics containing YPO4 nanocrystals for W-LEDs

Ce3+/Tb3+ co-doped transparent glass ceramics containing YPO4 nanocrystals were prepared using high temperature melting method, and their structural and luminous properties were investigated. XRD analysis and TEM images confirmed the existence of YPO4 nanocrystals in glass ceramics. The transmission spectra proved that the glass ceramics specimens still maintained a high transparency. Then the excitation and emission spectra of the Ce3+ and Tb3+ single-doped and co-doped glass and glass ceramics were discussed, which proved that the glass ceramics had better luminescent properties. Under the near ultraviolet (331 nm) excitation, the broadband emission located at 385 nm was observed which was ascribed to 5d→2F5/2 and 2F7/2 transition of Ce3+ ions. Several characteristic sharp peaks centered at 489, 543, 578 and 620 nm originated from the 5D4 to 7FJ (J=6, 5, 4, 3) of Tb3+ ions. The decay time of Tb3+ ions at 543 nm and the relevant energy levels of Ce3+ ions and Tb3+ ions illustrated the transfer process from Ce3+ ions to Tb3+ ions. The best CIE chromaticity coordinate of the glass ceramics specimen was calculated as (x=0.3201, y=0.3749), which was close to the NTSC standard values for white (x=0.333, y=0.333). All the results suggested that the YPO4-based Ce3+/Tb3+ co-doped glass ceramics could act as potential luminescent materials for white light-emitting diodes.

Up-conversion luminescence of Yb3+ and Er3+ doped YPO4, LaPO4 and GdPO4 nanocrystals

In this article we report a comparison of structural and up-conversion (UC) luminescence properties of three compounds used as hosts for Yb3+ and Er3+ ions: YPO4, LaPO4 and GdPO4 phosphates. A co-precipitation method connected with annealing at 900°C was used in order to synthesize nanocrystalline REPO4:Yb3+,Er3+ materials (RE=Y, La, Gd). The X-ray diffraction patterns collected for the prepared materials indicated their high crystallinity and phase purity for the wide range of used dopants concentrations (0.25–7.5% of Er3+ and 5–30% of Yb3+ ions). Transmission electron microscopy images showed small nanocrystal sizes: around 20nm for YPO4-based products, 30–50nm for LaPO4 or 40–150nm for GdPO4-based materials. The nanomaterials prepared showed yellow UC under 980nm laser irradiation, which was assigned to Er3+ electronic transitions. The optimal dopants concentration were determined, giving the highest UC intensity: 25% of Yb3+ ions (or 20% in the case of LaPO4) and 1% of Er3+ ions. Also the mechanism of observed UC was analyzed. Two- and three-photon excitation and energy transfer between Yb3+ and Er3+ were confirmed. The effect of crystal cell volume on the green to red ratio of Er3+ UC and the presence of Er3+–Er3+ energy transfer were found.

Enhancement of Luminescence of YPO<sub>4</sub>:Eu<sup>3+</sup>,Yb<sup>3+</sup> Nanophosphor Synthesized by Hydrothermal Method

YPO4 nanowires (NWs) and nanoparticles (NPs) have been synthesized by hydrothermal methods respectively in the absence and presence of EDTA. The Eu3+ and Yb3+ codoped YPO4 NWs and NPs prepared directly from hydrothermal systems show efficient red down-conversion luminescence (DL) and upconversion luminescence (UL) at room temperature without further annealing process. EDTA plays a critical role in controlling the morphologies of YPO4 nanocrystals in hydrothermal systems and enhances both the DL and UL intensities of Eu3+ by the factor of 100%. Monodispersed Eu3+ and Yb3+ codoped YPO4 NPs will be a new candidate for application in infrared displays and biological labels.

Laser heating of the Y_1-xDy_xPO_4 nanocrystals

We propose a novel material prepared by microwave-hydrothermal treatment, the tetragonal xenotime-type yttrium orthophosphate YPO4 nanocrystals doped by different concentrations of Dy3+. It may be suitable for laser-induced local heating of cancer tumors for hyperthermia. We heated a powder consisted of the nanoparticles by focused quasi-CW laser irradiation at different wavelengths in the near IR spectral range fitting the transparency window of biological tissues. The local temperature on the surface of the powder in the place of irradiation increases linearly with increasing laser power and increasing the Dy3+ concentration. At the same time the efficiency of local heating Φ = ΔT / (P f) (ΔT is a local temperature increase, f is an oscillator strength of absorption transition, and P is the quantity of laser power) is proportional to the energy of the initially excited electronic level. The proposed method allows for high rates of heating and cooling. The laser power used for heating was rather low, tens of milliwatts that together with short heating time to required temperature may result in extremely low doses of laser irradiation for heating.

Hidden local symmetry of Eu3+ in xenotime-like crystals revealed by high magnetic fields

The excellent optical properties of europium-doped crystals in visible and near infrared wavelength regions enable them to have broad applications in optoelectronics, laser crystals and sensing devices. The local site crystal fields can affect the intensities and peak positions of the photo-emission lines strongly, but they are usually difficult to be clarified due to magnetically degenerate 4f electronic levels coupling with the crystal fields. Here, we provide an effective way to explore the hidden local symmetry of the Eu3+ sites in different hosts by taking photoluminescence measurements under pulsed high magnetic fields up to 46 T. The zero-field photoluminescence peaks split further at high magnetic fields when the Zeeman splitting energy is comparable to or larger than that of the crystal field induced zero-field splitting. In particular, a magnetic field induced crossover of the local crystal fields has been observed in the GdVO4:Eu3+ crystal, which resulted from the alignment of Gd3+ magnetic moment in high magnetic fields; and a hexagonally symmetric local crystal fields was observed in the YPO4 nanocrystals at the Eu3+ sites characterized by the special axial and rhombic crystal field terms. These distinct Zeeman splitting behaviors uncover the crystal fields-related local symmetry of luminescent Eu3+ centers in different hosts or magnetic environments, which are significant for their applications in optics and optoelectronics.

Structural phase and morphology control of tetragonal and hexagonal YPO4:Eu nanoflakes for tunable luminescence properties

Eu3+-doped tetragonal and hexagonal YPO4 nanocrystals with different phase structures and morphologies were successfully synthesized by a solvothermal method. It was found that the pH value is a crucial factor in determining the phase structures and their morphologies of YPO4:Eu nanocrystals. The crystal structure and the properties of the Eu3+-doped YPO4 nanocrystals were characterized by XRD, SEM, TEM, UV–Vis spectroscopy.

Down- and up-converting dual-mode YPO4:Yb(3+),Tb(3+) nanocrystals: synthesis and spectroscopic properties.

Tetragonal YPO4 nanocrystals doped with Yb(3+) and Tb(3+) ions were synthesized by 900 °C annealing of precursors obtained with a co-precipitation method in the presence of glycerine. These materials exhibited intense green luminescence under ultraviolet excitation and up-conversion emission from the (5)D3 and (5)D4 Tb(3+) excited states after irradiation with near infrared light (λ = 980 nm). The structure and morphology of the products were analysed by recording X-ray diffraction patterns and transmission electron microscopy images. The obtained nanomaterials were single-phased with spherical shaped nanocrystals that had an average size of 18 ± 3 nm. The spectroscopic properties of YPO4:Yb(3+),Tb(3+) nanocrystals were investigated based on their excitation and emission spectra. The time-resolved luminescence traces were measured, and the luminescence lifetimes of Tb(3+) and Yb(3+) ions were calculated. The most effective dopant concentrations were determined to be 5% Yb(3+) and 15% Tb(3+), which exhibited the most intense ultraviolet excited emission and up-conversion. Because the integral intensity was observed to be dependent on the power of the pumping laser, a cooperative energy transfer (CET) mechanism underlying the observed up-conversion was proposed.

Luminescent Properties of Eu-Doped Transparent Glass-Ceramics Containing YPO4 Nanocrystals

Eu-doped transparent glass–ceramics containing YPO4 nanocrystals were prepared, and their structural and luminescent properties were investigated. Excited by 365 nm light, the precursor glass and glass–ceramics all emit an intense broad blue emission ascribing to 5d–4f transition of Eu2+ as well as characteristic sharp red emissions of Eu3+. The prominent Stark splitting, low forced electric dipole 5D0→7F2 transition and long decay lifetimes of Eu3+ emission demonstrated that Eu3+ had entered into YPO4 nanocrystals, while Eu2+ still reside in glass matrix. Our results indicate that YPO4-based glass–ceramics doped with lanthanide ions may find application in photonics.

Highly Enhanced Photoluminescence from YVO4:Eu3+@YPO4 Core/Shell Heteronanostructures

Novel YVO4:Eu3+@YPO4 core/shell heteronanostructures with enhanced photoluminescence (PL) are proposed in this paper. They were readily formed by hydrothermal epitaxial growth of YPO4 onto YVO4:Eu3+nanocrystals because YPO4 and YVO4 have the same crystal structure and similar lattice parameters. Characterizations by means of X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy prove that the as-synthesized products were not a mixture of YVO4:Eu3+ and YPO4 nanocrystals or YV1−xPxO4:Eu3+ (0 < x < 1) solid solutions, but YVO4:Eu3+@YPO4 core/shell heteronanostructures. The heteronanostructures exhibited much stronger PL than the YVO4:Eu3+ nanocrystals under the same conditions; the optimal heteronanostructures with a YPO4/YVO4:Eu3+ ratio of 1:6 yield a PL intensity 44% higher than that of the YVO4:Eu3+ nanocrystals. The YVO4:Eu3+@YPO4 heteronanostructures have some distinct advantages such as high degree of lattice matching between YVO4 and YPO4. Finally, we discuss the me...

Synthesis, structural and luminescence properties of Dy3+-doped YPO4 nanocrystals

Abstract Dy3+-doped YPO4 nanocrystals were synthesized by combustion method with urea as a fuel calcined at 600 °C. The as-prepared samples were characterized by X-ray diffraction (XRD), transmission electron micrograph (TEM) and photoluminescence (PL) spectroscopy. The obtained YPO4 nanocrystals appeared to be spherical with some agglomeration and their sizes ranged from 30 to 50 nm. The luminescence intensities were found to be strongly dependent on the concentration of Dy3+ ion and the additional quantities of urea.