Nguyen Vu

Nanomaterials containing rare-earth ions Tb, Eu, Er and Yb: preparation, optical properties and application potential

This paper focuses on preparation, optical properties and application potential of some nanomaterials based on Y2O3:Eu,Tb,Er,Yb and SiO2–TiO2 and SiO2–ZiO2 doped with Er and Yb. Y2O3 nanophosphors are prepared by the combustion method with different doped concentrations. The nanocrystal size of Y2O3:Eu is from 4.4 to 72.2 nm depending on the technology condition. The luminescent spectra, up-conversion and lifetimes were measured and compared. The influence of the technological conditions on the luminescent properties was investigated in detail. The energy transfer effect was studied by the luminescent spectra and the lifetimes in the temperature dependence for the samples with rare-earth concentrations of 5 mol%, The relative concentration between Eu and Tb is 8/2 for energy transfer from Tb to Eu. The SiO2–TiO2 and SiO2–ZiO2 thin films containing Er rare-earth ion were prepared by the sol–gel technique. Optical properties were investigated and the influence of the Er concentration on the luminescent spectra as well as the influence of the Ti concentration on the refractive index of thin films was presented.

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.

Preparation and optical properties of one dimensional nano hydroxides and oxides

The Yttrium hydroxide nanotubes and nanorods as well as the ZnO nanorods and nanowires were prepared by different methods. Y(OH)3 nanotubes and nanorods were synthesized by polyol — mediation via the metastable precursor YCl3, PEG and were studied by FE SEM and XRD. The influence of the polymer molecular weights of PEG and the temperature were studied in detail. These results show that the first stage is nanorods, then it is followed by the formation of nanotubes. The outer diameter of the tubes is about 150 nm to 600 nm and interior hollow is in the range between 100 nm to 300 nm. The length of the rods and the tubes is up to several micrometers. We have found that the synthesis temperature, reaction rate and molecular weight of PEG induce the change in shape of obtained nanotubes from a cylindrical to a hexagonal appearance. The growth process of the nanotubes may be performed through three stages: first complexing the PEG polymer with Y(NO3)3, then hydrolysis for formating Y(OH)3 nanorods and finally diffusion-controlled developing of Y(OH)3 nanotubes. The ZnO nanorods were prepared by Chemical Vapor Deposition (CVD) and Metal Organic Chemical Vapor Deposition (MOCVD) method, respectively. Aligned growth of ZnO nanorods has been successfully prepared. The nanorods have the diameters of about 50 nm and the length of about 1.12 micrometers. The influence of the temperature is investigated. The luminescent spectra (excited by Cd-He laser at 325 nm) of ZnO nanorods at 10 K- 300 K was measured and investigated. The sharp peak is assigned to an exciton bound to a neutral donor.

Preparation, optical properties and structure of Y/sub 2/O/sub 3:Eu and Y/sub 2/O/sub 3/:Tb,Eu nanophosphors

Y₂0₃:Eu powder was prepared with varying concentrations of Eu of 3,5 and 7 mole %, and Y₂0₃:Tb,Eu (y=0.95, Eu+Tb=0.05) with mole ratios of Eu/Tb of 7/3,8/2, 9/1, by the combustion method. The luminescent intensity, the decay time of Eu, Tb and the energy transfer between Tb and Eu in the Y₂0₃:Eu,Tb powder were studied. For Y₂0₃:Eu at different annealing conditions, the average particle sizes were from 4.4nm to 2.2nm. The luminescent intensity of Y₂0₃:Eu, Tb nanophosphors is a maximum in the case of a mole ratio of Eu/Tb of 8/2. The influence of the preparation conditions on the optical and structural properties was investigated.