BaYF5 Nanocrystals Research Articles

Structure, morphology, photonconversion and energy transfer characteristics of Er3+/Yb3+:BaYF5 nanocrystals synthesized by hydrothermal method for photovoltaics

Lanthanide doped nanocrystalline fluoride optical materials have been explored for diverse applications in the solar energy harvesting, industry, medical, forensic and biological fields because of high photoluminescence quantum yield and low phonon energy. In this manuscript, Er3+/Yb3+:BaYF5 nanocrystals were synthesized by hydrothermal process. These nanocrystals were investigated through X-ray diffraction (XRD), SEM/TEM, Raman, quantum yield, photoluminescence upconversion (UC) and downconversion (DC) studies. XRD patterns exhibited the cubic phase and no phase deviation with the addition of Er3+ and Yb3+ ions. The TEM images illustrate the cubic-like morphologies of the obtained nanocrystals. Raman spectrum unveils the characteristic vibrational bands with an intense band at 498 cm−1, which is considered the phonon energy of the BaYF5 matrix. Under 488 nm excitation, the near infrared (NIR) emission of Er3+ increases up to 5 mol% and then decreases for a 10 mol% doped sample. Photoluminescence DC quantum yield of Er3+/Yb3+:BaYF5 sample is measured by using integrating sphere in the visible region under 488 nm (Xe flash lamp) excitation, is 4.25%. Under 900 nm laser excitation, intense NIR emissions at 978 and 1550 nm corresponding to Yb3+ (2F5/2 → 2F7/2) and Er3+ (4I13/2 → 4I15/2) ions, respectively, were observed. With the increase of Yb3+ concentration, the NIR emissions of both Er3+ and Yb3+ increase to 5 mol% and then decrease to 10 mol%. The strength of green UC emission of Er3+ decreases with increase of Er3+ concentration, whereas it enhances with the rise of Yb3+ concentration under 980 nm laser excitation. Two-photon UC process is confirmed as the slopes of the green, and red intensities are 2 and 2. These nanocrystals exhibit intense UC and DC emissions under 980 nm and 480 nm, respectively, which can be suitable for improving the efficiency of solar cells.

Er3+‐Yb3+ ions doped fluoro‐aluminosilicate glass‐ceramics as a temperature‐sensing material

AbstractThe transparent Er3+‐Yb3+‐doped fluoro‐aluminosilicate glass‐ceramic (GC) was prepared by melt‐quenching. The crystal phase, morphology, and up‐conversion (UC) luminescence of as‐produced GC were characterized by X‐ray diffraction, scanning electron microscopy, and fluorescence spectrophotometry, respectively. The results show that BaYF5 nanocrystals were uniformly distributed in the glass matrix of the as‐produced GC. When the as‐produced GC was subjected to heat treatment, the crystallinity was increased, but the crystal identity remains unchanged. Such heat‐treatment doubled the intensity of the UC luminescence, and this enhancement was ascribed to the increased incorporation of both Er3+ and Yb3+ ions into the lower phonon energy environment of BaYF5 nanocrystals. Furthermore, the heat‐treated GC was stable against further crystallization, and consequently its UC luminescence was stable at the application temperature. The heat‐treated GC was found to possess an outstanding temperature‐sensing capability.

Deciphering the role of temperature in Li+ co-dopant occupancy in BaYF5:Yb3+,Er3+ up-converting nanocrystals and its structure-property relationship.

Precision engineering of defects in luminescent nanoscale crystalline materials with lesser controls to design is an area of interest in engineering materials with desired properties. Li+ co-doped BaYF5 nanocrystals were engineered, and temperature as controls for determining the co-dopant occupancies in the host lattice is studied. An observed enhancement in the up-conversion photoluminescence results from the co-dopant occupancy at Ba2+ sites via substitution through the hot injection method, whereas for samples prepared using co-precipitation, photoluminescence quenching was observed, which can be correlated with the Li+ occupancy at the interstitial site near Er3+ and also due to the incorporation of OH-. The crystal lattice deformation as a result of doping and the mechanism for the observed enhancement/quenching of luminescence are studied using x-ray diffraction, x-ray photoelectron spectroscopy, and energy transfer mechanism. Cytotoxicity assay and photoluminescence studies of the synthesized nanocrystals confirm that the material is biocompatible.

Structure, morphology and optical characterization of Dy3+-doped BaYF5 nanocrystals for warm white light emitting devices

The barium yttrium fluoride BaYF5 nanocrystalline powders doped with different concentrations of Dy3+ ions have been synthesized via a hydrothermal method and studied their structural, morphological, thermal, vibrational, and optical properties. These nanopowders have been crystallized in a single phase of the tetragonal structure with the average size of around 30 nm having spherical shape in morphology. Upon excitations at 350 and 387 nm, Dy3+ -doped BaYF5 nanocrystals exhibit strong blue and yellow emissions ascribed to the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions, respectively. Decay curves of the 4F9/2 level of Dy3+ ion in BaYF5 nanocrystals exhibit non-exponential nature due to the dipole-dipole interaction between Dy3+ ions, confirmed by Inokuti-Hirayama model. The quantum yield for these nanocrystals have been found to be increased from 4.64% to 11.61% as the concentration of Dy3+ ions increases from 1.0 mol% to 2.0 mol% and then decreased to 10.68% as the dopant concentration increased to 5.0 mol%. Moreover, color coordinates and correlated color temperatures have been evaluated as a function of concentration and excitation wavelength and found to be in the warm white light region for all Dy3+ concentrations.

A facile synthesis of water-soluble BaYF5:Ln3 + NCs with excellent luminescent properties as promising contrast agent for dual-modal bioimaging

Monodisperse, water-dispersible lanthanide (Ln3+)-doped BaYF5 nanocrystals (NCs) are synthesized through a fast, facile and environmentally–friendly microwave-assisted modified polyol process with polyethyleneimine as the surfactant. The TEM images illustrate the sphere-like and flower-like morphologies of the obtained NCs. Intense multicolor down conversion (DC) luminescence is also achieved in Ce3+/Ln3+ (Ln=Tb, Dy) doped BaYF5 NCs. Then, upon excitation at 980nm, upconversion (UC) luminescent properties of BaYF5:Yb3+/Ln3+ (Ln=Er, Tm, Ho) NCs and energy transfer between Yb3+ and Ln3+ are systematically surveyed. Furthermore, a layer of SiO2 is coated on the surface of the NCs and the methyl thiazolyl tetrazolium (MTT) assays are performed to test the cytotoxicity of BaYF5:Ln3+ NCs. Due to the X-ray absorption property of Ba element, a proof-of-concept CT imaging with BaYF5:Ln3+ NCs is conducted. These results indicate that the obtained NCs have great potential as optical/CT bioprobe.

Upconversion luminescence in BaYF5, BaGdF5 and BaLuF5 nanocrystals doped with Yb3+/Ho3+, Yb3+/Er3+ or Yb3+/Tm3+ ions

Nanomaterials based on BaREF5 fluorides (where RE = Y, Gd and Lu), doped with lanthanide ions Yb3+/Ln3+ (Ln3+ = Er, Ho or Tm) were synthesized by microwave assisted hydrothermal method. The method of synthesis, structural and morphological properties are reported and discussed. The products obtained showed visible upconversion luminescence excited by the laser light of wavelength of 975 nm as a consequence of energy transfer between Yb3+ and remaining Ln3+ dopant ions. Their spectroscopic properties were characterized on the basis of excitation and emission spectra. Also luminescence decays and emission power dependences are presented and analysed. The materials compared revealed differences in their structural properties, reflected in their spectroscopic characteristics. The most intense luminescence was recorded for BaLuF5 based materials which exhibited upconversion also as water colloids.

Site selective spectroscopy in BaYF5:RE3+ (RE = Eu, Sm) nano-glass–ceramics

Trivalent rare-earth (RE=Eu, Sm) doped transparent nano-glass–ceramics comprising BaYF5 nanocrystals were successfully obtained by appropriate heat-treatment of the corresponding precursor sol–gel glasses. Their structural and spectroscopic properties were investigated and compared with those for Eu3+-doped-BaYF5 nanocrystals prepared by a solvothermal method. X-ray Diffraction, Transmission Electron Microscopy and Energy Dispersive X-ray Spectroscopy measurements confirmed the distribution of BaYF5 nanocrystals in the glass matrix, presenting a cubic phase structure with space group Fm-3m. In order to achieve a further structural characterization, the luminescence properties of the Eu3+ and Sm3+ dopants were also used as sensitive probes. The reduction in the emission intensities of hypersensitive transitions 5D0→7F2 and 4G5/2→6H9/2 for Eu3+ and Sm3+ ions respectively, along with time-resolved measurements, confirm the distribution of a significant fraction of RE ions into the fluoride nanocrystal environment. These results suggest that BaYF5 nano-glass–ceramics doped with Eu3+ or Sm3+ can be considered as potential red-emitting phosphors for the development of white LEDs under near UV excitation.

Microwave-assisted synthesis and down- and up-conversion luminescent properties of BaYF5:Ln (Ln = Yb/Er, Ce/Tb) nanocrystals

Hydrophilic BaYF5 nanocrystals have been prepared via a facile and fast microwave-assisted method at low temperature without the assistance of template reagents. The Yb3+/Er3+, Ce3+/Tb3+ doped BaYF5 nanocrystals could be dispersed well in water and alcohol. BaYF5:Ce3+/Tb3+ nanocrystals show bright green luminescence. The existence of the Ce3+ ions can dramatically enhance the luminescence intensity of the Tb3+ ions, due to the efficient energy transfer from Ce3+ to Tb3+ ions. More importantly, when doped with Yb3+/Er3+ ions, the BaYF5 nanocrystals show bright red upconversion luminescence.

Luminescence properties of Pr3+-doped transparent oxyfluoride glass–ceramics containing BaYF5 nanocrystals

Transparent oxyfluoride glass–ceramics containing BaYF5 nanocrystals were successfully synthesized by appropriate heat-treatment on the SiO2–Al2O3–Na2O–BaF2–Y2O3–Pr6O11 precursor glass. The structure and luminescence properties of the precursor glass and glass–ceramics were investigated by DSC, XRD, TEM, optical transmission, photoluminescence, decay time and radioluminescence spectra. The XRD results indicate that the BaYF5 nanocrystals can percitated in the precursor glass and the sharper emission peaks of Pr3+ in glass ceramic suggests that Pr3+ ions are incorporated into the BaYF5 nanocrystals. The higher the heat-treatment temperature is, the more the Pr3+ ions are centered into BaYF5 nanocrystals, which results in the optimal concentration of Pr3+ in glass ceramic changes on heat-treatment temperature. It is notable that the emission intensity of both photoluminescence and radioluminescence for 0.1mol% Pr3+ in the glass ceramic (GC665) are stronger than those in the precursor glass. The mechanism of enhanced luminescence is also discussed.

Synthesis and Structural Probing of Eu3+ Doped BaYF5 Nano‐Crystals in Transparent Oxyfluoride Glass‐Ceramics

Transparent oxyfluoride glass‐ceramics containing Eu: BaYF5 nano‐crystals in the newly developed SiO2–K2CO3–BaF2–YF3–Sb2O3 glass system are synthesized by melt quenching method followed by optimized ceramization process. The X‐ray diffraction, transmission electron microscopy, and field emission scanning electron microscopy confirmed the precipitation of tetragonal BaYF5 nano‐crystals in glass matrix. The coexistence of Eu2+ and Eu3+ ions in both glass and glass‐ceramics are ascertained from their emission and excitation spectra. The in situ formation of divalent europium (Eu2+) along with Eu3+ during high temperature synthesis under ambient atmosphere is explained through optical basicity model. The Eu3+ emission from upper excitation states (5D3−1) and reduced asymmetry ratio (R = IED/IMD) in glass‐ceramics have established the dopant ion incorporation into fluoride nano‐crystalline environment. The observed luminescence properties of Eu:BaYF5 are compared with that of Eu:BaYF5 nanocrystals containing transparent glass‐ceramics and their marked differences are discussed.

Controllable and white upconversion luminescence in BaYF5:Ln3+(Ln = Yb, Er, Tm) nanocrystals

BaYF5:Yb3+, Er3+, Tm3+ nanocrystals have been successfully synthesized via a hydrothermal process. SEM and TEM images indicate that the size of the nanocrystals is about 20 nm. Under the excitation of a 980 nm single-wavelength diode laser, BaYF5:Er3+ nanocrystals give strong green upconversion (UC) emission centered at 523 and 541 nm, which is assigned to 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions of Er3+, respectively. When Yb3+ is codoped in BaYF5:Er3+, red emission around 652 nm can be observed in the emission spectrum. This emission can be assigned to the 4F9/2 → 4I15/2 transition of Er3+. The intensity ratio of the green luminescence to the red luminescence decreases with increasing Yb3+ concentration in BaYF5:Yb3+, Er3+ nanocrystals. The blue UC emissions of BaYF5:Yb3+, Tm3+ nanocrystals appeared near 464 and 480 nm and are assigned to the 1D2 → 3F4 and 1G4 → 3H6 transitions of Tm3+, respectively. Based on the generation of red, green, and blue emissions, the BaYF5:Yb3+, Er3+, Tm3+ nanocrystals can produce different colors, including white, by controlling the doping concentration of Yb3+ in the BaYF5 nanocrystals. The BaYF5:40%Yb3+, 0.5%Er3+, 0.5%Tm3+nanocrystals show proper intensities of blue, green, and red emissions, which result in the production of white light (CIE: x = 0.346, y = 0.336).

Ethylenediaminetetraacetic acid (EDTA)-controlled synthesis of multicolor lanthanide doped BaYF5 upconversion nanocrystals

Here lanthanide-doped tetragonal nanocrystals of BaYF5 with strong near infrared-to-visible multicolor upconversion emissions have been controllably synthesized by a hydrothermal method. Opposite to well-established NaYF4 nanocrystals, we found that the sizes of the BaYF5 nanocrystals increase in proportion to that of the molar ratios of EDTA to lanthanide nitrates and decrease as the pH value of the precursor solution increases in presence of EDTA. These findings reveal that the nucleation process of BaYF5 nanocrystals is governed by the pH-sensitive chelating ability of EDTA with both Ba2+ and Ln3+. Additionally, it was found that single wavelength laser excitation of 980 nm can induce strong red, green, and blue upconversion emissions in BaYF5 nanocrystals doped with 18%Yb3+/2%Er3+, 18%Yb3+/2%Ho3+, and 18%Yb3+/2%Tm3+, respectively. Furthermore, after a facile surface poly(acrylic acid) ligand exchange reaction, such multicolor nanoparticles can be transferred into water and multiple other solvents for applications in biology and materials science.

Hydrothermal Synthesis, Cubic Structure, and Luminescence Properties of BaYF5:RE (RE = Eu, Ce, Tb) Nanocrystals

BaYF5 nanocrystals with a mean size of about 24 nm have been prepared via a facile hydrothermal method without the assistance of any surfactant for the first time. The structure investigation reveals that the as-synthesized BaYF5 nanocrystals are cubic structures instead of the reported tetragonal structures found via a Rietveld refinement method with GSAS, a Rietveld refinement package. The XRD and SEM analyses demonstrate that the size and morphology of the products are insensitive to the variation of experimental conditions. The photoluminescence properties of the Eu3+, Ce3+, and Tb3+ single-doped as well as Ce3+-Tb3+ codoped BaYF5 nanocrystals were characterized. The results reveal that the existence of the Ce3+ ions can dramatically enhance the emission intensity of the Tb3+ ions, due to an efficient energy transfer from the Ce3+ to Tb3+ ions in the BaYF5:Ce3+,Tb3+ nanocrystals. The critical energy transfer distance between the Ce3+ and Tb3+ ions was calculated by methods of concentration quenching a...

Synthesis of LiYF<SUB>4</SUB>, BaYF<SUB>5</SUB>, and NaLaF<SUB>4</SUB> Optical Nanocrystals

This paper reports the synthesis of high quality LiYF4, BaYF5, and NaLaF4 nanocrystals by high-temperature co-decomposition of precursors in organic solvents. Their bulk counterparts have long been used as efficient luminescent hosts for various applications including lasers, upconversion fluorescence, and quantum cutters. The particles were characterized using TEM, XRD, dynamic light scattering (DLS), and fluorescence spectrometry. Trifluoroacetic acid (CF3COOH) and the reaction temperature were crucial for the formation of NaLaF4 and LiYF4 nanoparticles. NaLaF4 was not formed without using CF3COOH, only LaF3 and NaF mixture was formed. NaLaF4 nanoparticles were obtained only when CF3COOH was added in the reaction solution and the temperature was > or =330 degrees C. For the synthesis of LiYF4,, in the absence of CF3COOH in the reaction, a mixture of YOF and LiYF4 nanoparticles was formed. Pure LiYF4 particles were obtained only until CF3COOH was added in the reaction at 340 degrees C or above. The nanoparticles were easily dispersed in organic solvents include hexane, toluene, and chloroform and formed transparent colloidal solutions. The ease of doping of these as-synthesized host nanoparticles for designed optical properties was assessed. The LiYF4, BaYF5, and NaLaF4 nanoparticles, co-doped with 20% Ytterbium (Yb) and 2% Erbium (Er), showed bright upconversion fluorescence upon 980 nm NIR excitation, confirming the high quality of as-synthesized nanoparticles. These nanoparticles are potential candidates for nano-optical devices, thin films, telecommunication, and bio-probes.