Tran Kim Anh

Luminescence, energy transfer, and upconversion mechanisms of Y 2 O 3 nanomaterials doped with Eu 3+ , Tb 3+ , Tm 3+ , Er 3+ , and Yb 3+ Ions

Luminescence, energy transfer, and upconversion mechanisms of nanophosphors (Y2O3:Eu3+, Tb3+, Y2O3:Tm3+, Y2O3:Er3+, Yb3+) both in particle and colloidal forms were studied. The structure, phase, and morphology of the nanopowders and nanocolloidal media were determined by high-resolution TEM and X-ray diffraction. It was shown that the obtained nanoparticles have a round-spherical shape with average size in the range of 4 to 20nm. Energy transfer was observed for Y2O3:Eu3+, Tb3+ colloidal and powders, upconversion transitions were observed for both Y2O3:Er3+ and Y2O3:Er3+, Yb3+ nanophosphors. The dependence of photoluminescence (PL) spectra and decay times on doping concentration has been investigated. The infrared to visible conversion of emission in Y2O3:Er3+, Yb3+ system was analyzed and discussed aiming to be applied in the photonic technology.

Luminescent nanomaterials containing rare earth ions for security printing

The high-efficiency luminescent nanomaterials with different emission wavelengths of red (YVO4:Eu3+), green (CePO4:Tb3+), ZnS:Mn2+ and YVO4:Eu3+;@SiO2 were successfully prepared with different concentrations of Mn and rare earth ions as active centres by chemical synthesis. Structure properties were studied. It was found that the particle size of our samples was in the range of 10-30 nm. Photoluminescent properties were studied under 325, 337, 365 and 370 nm excitations in order to apply in luminescent labels. The primary colour components are red and green emission making them very convenient and attractive for screen security printing systems. Hundreds of different labels with a size of 1-10 cm² were prepared by screen-printing as well as inkjet printing. By improving the Epson printer, commercial red, green and blue inks were used in the printing application. Screen and inkjet printing were deemed good methods for security printing. Our products were beautiful, high resolution and withstood tropical weather.

Energy transfer and dynamic luminescence of material containing rare earth ions used in X-ray medical imaging

Abstract LaOBr : Tb, Bi and BaFCl: Eu are two luminescence materials which show interesting optical properties like energy transfer and photostimulated luminescence. They are also well known materials for the intensifying screens used in X-ray medical imaging. Four polycrystalline LaOBr: Tb, Bi with different concentration of Bi and Tb as well as ten samples of BaFCl: Eu with different Eu concentration have been synthesized. Energy transfer between Bi and Tb will be investigated in detail for LaOBr: Tb,Bi. Nonexponential decays were observed. The time resolved luminescence spectra and decay time of BaFCl: Eu will be presented. The intensifying screens of BaFCl: Eu with different sizes were prepared. They were used in some hospitals of Viet Nam with short time X-ray exposure, low afterglow and are suitable in the tropical conditions.

Fabrication and optical characterization of multimorphological nanostructured materials containing Eu(III) in phosphate matrices for biomedical applications

EuPO4·H2O nanorods/nanoparticles with a rhabdophane-type hexagonal form have been successfully synthesized using microwave assisted co-precipitation. The effects of chemical composition and pH on the size, shape, morphology and luminescence properties have been investigated by powder X-ray diffraction, Field Emission Scanning Electron Microscopy (FESEM), and photoluminescence spectroscopy. The mean size of the nanorods is about 15–30 nm in diameter and 200–400 nm in length and the size of nanoparticles is 10–20 nm. A powdered sample of these EuPO4·H2O nanorods/nanoparticles emitted yellow-green light with narrow bands at 594, 619, 652, and 697 nm under UV-vis excitation. The surface effects of the built core–shell structure on the fluorescent properties, and the compatibility of the EuPO4·H2O nanomaterials with a biological system, have been studied to develop a new fluorescent label for biomedical imaging. The primary test results in using a EuPO4·H2O–Immunoglobulin G conjugate for recognizing the measles virus in a vaccine is presented.

Fabrication and optical characterisation of SiO2 opal and SU-8 inverse opal photonic crystals

High-quality photonic crystals of SiO2 spheres and air spheres are fabricated using self-assembling processes and infiltration method with thermal-assistant cell method. Their photonic band structures are characterised by reflectivity spectra measurements. It shows that the tunable optical stop bands are determined by refractive index contrast, diameter of spheres and angle of light illumination. The experimental results of reflectivity spectra agree very well with the results obtained by theoretical Bragg diffraction and photonic band calculations.

Fabrication and characterization of YVO4:Eu3+ nanomaterials by the micro-wave technique

Abstract Fabrication and characterization of YVO 4 :Eu 3+ nanophosphors prepared by microwave (MW) irradiation assisted soft template synthesis were reported. The effects of synthesis conditions such as different powers of MW irradiation, pH values and concentration of reaction materials on properties of nanophosphor were also investigated to obtain the controllable size, morphology and high luminescence efficiency. Morphology, crystalline structure, and optical properties were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and fluorescence spectroscopy, respectively. The results showed that YVO 4 :Eu 3+ nanophosphors were obtained by using diethyleneglycol (DEG) as soft template, with pH values in the range of 4 to 12, upon microwave irradiation from 300 to 900 W, at temperature of 80 °C. The high fluorescent YVO 4 :Eu 3+ nanocrystals obtained with size from 15 nm down to 8 nm are more effective to develop an ultrahigh sensitive fluorescent label for biomolecule, cell and tissue.

Synthesis and characterization of core/shell structured nanophosphors CePO4:Tb@LaPO4 by solvothermal method

Abstract Core/shell structured CePO4:Tb(III)@LaPO4 and CePO4:Tb(III) were successfully synthesized in tris(2–ethylhexyl) phosphate (TEHP) and diethylene glycol (DEG) solvents for comparison of the two techniques in open air and closed reaction vessel. Morphology and crystal structure of the core/shell nanophosphors were determined by using X-ray diffraction (XRD) and transmission electron microscopy (TEM), which showed that nanophosphors had diameter of about 5–10 nm with the monoclinic monazite phase. The nanophosphors obtained by close vessel procedure showed smaller size, more homogeneity and pure crystallite. The luminescent measurements were done upon the different excitation wavelengths in ultraviolet region and at room temperature to elucidate the influences of the used solvents and the reaction temperatures. It was found that CePO4:Tb@LaPO4 prepared by the close vessel synthesis showed the intensity of green band of the transfer from 5D4 to 7F5 energy level, which was strongly increased, and the luminescent decay time was 3.2 ms, which was longer than that of naked CePO4:Tb phosphor.

Fabrication and properties of high efficiency luminescent nanorods EuPO4·H2O by soft template method

Abstract Europium orthophosphate monohydrate (EuPO 4 ·H 2 O) nanorods with typical dimensions of about 10–30 nm in diameter and 300–500 nm in length were prepared by using the soft template method. The effects of using diethylene glycol (DEG) and polyethylene glycol (PEG) polymers as well as the pH values on the size, crystalline structure and morphology of EuPO 4 ·H 2 O nanorods were investigated. Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) data of the prepared samples were elucidated. The nanorods were highly uniform and their mean length was reduced by using DEG and PEG as soft template agents. For all prepared samples, the rhabdophane-type hexagonal EuPO 4 ·H 2 O was the dominated phase. The photoluminescence (PL) spectroscopy measurements of EuPO 4 ·H 2 O nanorods revealed that, under UV excitation, EuPO 4 ·H 2 O nanorods exhibited strong luminescence with narrow bands corresponding to the intra-4f transitions of 5 D 0 → 7 F j ( j =1, 2, 3, 4) of Eu 3+ ions. The peaks were found at 594 nm ( 5 D 0 → 7 F 1 ), 619 nm ( 5 D 0 → 7 F 2 ), 652 nm ( 5 D 0 → 7 F 3 ), and 697 nm ( 5 D 0 → 7 F 4 ), with the strongest emission at 594 nm.

Fabrication and properties of highly luminescent materials from Tb(OH)3@SiO2 and Tb(OH)3@SiO2:Eu3+ nanotubes

Luminescent nanomaterials with one-dimensional (1D) structures have attracted much attention due to their unique properties and potential applications in nanophotonics and nanobiophotonics. In this paper, we report a synthesis of terbium – hydroxide – at – silica Tb(OH)3@SiO2 and Tb(OH)3@SiO2:Eu3+ nanotubes. Terbium – hydroxide tubes were synthesized by soft template method. The size of the tubes can be controlled precisely and have outer diameters ranging from 80 to 120 nm, wall thickness of about 30 nm, and lengths ranging from 300 to 800 nm. To fabricate core/shell materials, the seed growth method is used. FESEM, X-ray diffraction, Raman spectra of Tb(OH)3 and Tb(OH)3@SiO2 nanotubes were investigated. The photoluminescence (PL) spectrum of Tb(OH)3 under 325 nm excitation consists of four main peaks at 488, 542, 582, and 618 nm. Furthermore, a preliminary suggestion for the mechanism of growth of the Tb(OH)3 nanotubes using the soft – template synthesis technique has been proposed. The PL intensity from Tb(OH)3@SiO2 or Tb(OH)3@SiO2:Eu3+ nanotubes is much stronger than that of Tb(OH)3.

Fabrication and upconversion emission processes in nanoluminophores NaYF4: Er, Yb and NaYF4: Tm, Yb

In this paper we present the new results of fabrication, characterisation and upconversion emission process of NaYF4 nanoparticles doped with Er3+ or Tm3+and Yb3+ as sensitiser. In order to fabricate α–, β–NaYF4:2%Er3+, 19%Yb3+and α–, β–NaYF4:2%Tm3+, 19%Yb3+ nanoparticles the soft template method in isopropylamine at 140C and diethylene glycol (DEG) at 180C has been used. The morphology, structures and emission properties were studied by X–ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and luminescence spectroscopy. The upconversion luminescence (UCL) spectra of α and β crystalline forms of NaYF4:2%Er3+, 19%Yb3+and NaYF4:2%Tm3+, 19%Yb3+ nanoparticles were investigated upon diode laser excitation at 976 nm. The strong emissions in the green and red spectral regions were observed upon this excitation. The spectral lines of the UCL could be assigned to the upconversion radiative transitions of the Er3+ or Tm3+ ions with Yb3+ sensitiser. The upconversion emission spectra dependent on laser excitation powers have been investigated in order to elucidate the upconversion emission paths which could take place. We found the significant influence of the type of nanocrystalline structure on the upconverting radiative transition mechanisms in NaYF4:2%Er3+, 19%Yb3+and NaYF4:2%Tm3+, 19%Yb3+ nanoparticles.