In this paper, we report the obtention of gadolinium oxide doped with
europium (Gd2O3:Eu+3) by thermal decomposition
of the Gd(OH)3:Eu3+ precursor prepared by the microwave
assisted hydrothermal method. These systems were analyzed by
thermalgravimetric analyses (TGA/DTA), X-ray diffraction (XRD), structural
Rietveld refinement method, fourrier transmission infrared absorbance
spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM) and
photoluminescence (PL) measurement. XRD patterns, Rietveld refinement analysis
and FT-IR confirmed that the Gd(OH)3:Eu3+ precursor
crystallize in a hexagonal structure and space group P6/m, while the Gd2O3:Eu3+ powders annealed in range of 500°C and 700°C crystallized in a cubic
structure with space group Ia-3. FE-SEM images showed that Gd(OH)3:Eu3+ precursor and Gd2O3:Eu3+ are composed by
aggregated and polydispersed particles structured as nanorods-like morphology.
The excitation spectra consisted of an intense broad band with a maximum at 263
nm and the Eu3+ ions can be
excitated via matrix. The emission spectra presented the characteristics
One-dimensional nanomaterials, such as nanotubes, nanowires, nanobelts or nanoribbons have attracted much interest in the past decade due to their physical properties and potential applications in nanotechnology fields [
The demand for efficiency and high resolution waveguides, lamps and other optical devices has also stimu- lated the discovery of new luminescent materials with superior properties. Thus, there has been a tremendous interest in the subject of materials science for the development of new luminescent materials. The improved performance of display requires high-quality phosphors for sufficient brightness and long-term stability. To en- hance the luminescent characteristics of phosphors, extensive research has been carried out on rare-earth acti- vated oxide phosphors due to their superiority in color purity, chemical and thermal stabilities [
In particular, the gadolinium oxide doped with Eu3+ (Gd2O3:Eu3+) exhibits a strong paramagnetic behavior (S 1/4 72) as well as strong UV and cathode-rays have also been observed in the lanthanide (Sm3+, Er3+) doped Gd2O3 excited luminescence, which are useful in biological fluorescent label, contrast agent, and display appli- cations [
Europium ion in a trivalent state is one of the most studied rare earth element because of the simplicity of its emission spectra and due to the wide application as red phosphor in color TV screens. Eu3+ f-f transitions are sensitive to its local environment. The monitoring of different concentrations of the Eu3+ content into a ceramic material is very interesting in understanding the nature of the lattice modifiers as well as the degree of or- der-disorder into its crystalline structure. The most intense f-f transition is the
A variety of preparation methods have been developed to reduce the reaction temperature and achieve a small particle size of high quality Gd2O3:Eu3+ phosphors [
Microwave heat processing has been successfully applied for the preparation of micro or nanosized inorganic materials [
In the present work, we investigated the photo-physical properties of Gd2O3: Eu3+ phosphors obtained by the thermal decomposition in range of 500˚C and 700˚C of the Gd(OH)3:Eu3+ precursor prepared by the microwave assisted hydrothermal method. These materials were structured and microstructurally analyzed by means of X-ray diffraction (XRD), Rietveld refinement method, fourrier transmission infrared absorbance spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM). The photo-physical properties were investigated through the excitation and emission spectra of the Eu3+ ion as well as lifetime measurements.
The synthesis of the precursors was performed using the following procedure: In a typical synthesis, 1.8 g of Gd2O3 and 0.018 g of Eu2O3 were dissolved in 3.0 mL of the HNO3 solution. After the formation of a clear solu- tion, this solution was kept under constant heating until complete evaporation of the acid. Then 80 mL of dis- tilled water were added to the solution and stirred for 30 min at room temperature. After that, an aqueous KOH (2.0 M) solution was added until the pH of solution was adjusted to be in the range of 12 giving rise to a col- loidal precipitates. After stirring for about 30 min, the resultant solution was transferred to a Teflon lined stain- less autoclave. This autoclave was then sealed and placed into a microwave system (MH) using 2.45 GHz mi- crowave radiation with maximum power of 800 W. The MH conditions were kept at 140˚C for 1 minute. The white powders obtained (Gd(OH)3:Eu3+) were collected, washed with water and ethanol, and then dried at 60˚C for 8 h under atmospheric air in a conventional furnace.
The Gd2O3:Eu3+ powders were obtained from thermal decomposition of the Gd(OH)3:Eu3+ precursors. These precursor powders were placed in ceramic crucibles and heated in a microwave sintering furnace at 500˚C, 550˚C, 600˚C, 650˚C and 700˚C for 5 min under an ambient atmosphere using a heating rate of 5˚C/min pro- ducing white powders denoted as Gd2O3:Eu3+.
The Gd(OH)3:Eu3+ and Gd2O3:Eu3+ powders were structurally characterized by X-ray diffraction (XRD) in nor- mal routine and Rietveld routine using a Rigaku-DMax/2500PC (Japan) with Cu-Kα radiation (λ = 1.5406 Å) and in the 2θ range from 10˚ to 130˚ with a scanning rate of 0.02˚/min. Fourier Transmission Infrared absorbance spectroscopy (FT-IR) analysis were taken in a FT-IR Bruker model EQUINOX spectrophotometer in range of 500 and 4000 cm−1. Crystals morphologies were verified using a Scanning Electron Microscope (Jeol JSM-6460LV microscope). Photoluminescence (PL) was measured with a Thermal Jarrel-Ash Monospec 27 monochromator and a Hamamatsu R446 photomultiplier. The 350.7 nm exciting wavelength of a krypton ion laser (Coherent Innova) was used, with the nominal output power of the laser power kept at 200 mW. All the measurements were taken at room temperature. The excitation and emission spectra of the Gd2O3:Eu3+ powders were measured in a Jobin Yvon-Fluorolog 3 spectrofluorometer at room temperature using a 450 W xenon lamp as excitation energy source. Lifetime data of the Eu3+
In summary, the obtained results showed that the Gd(OH)3:Eu3+ (precursor) was synthesized by the microwave assisted hydrothermal method in a short period of time (30 minutes). After heated treated from 500˚C to 700˚C,
Emission spectra of Gd2O3:Eu3+ samples calcined at 500˚C, 550˚C, 600˚C, 650˚C and 700˚C, lex = 263 nm
Decay curves and lifetime of the 5D0 → 7F2 transition characteristic of the Eu3+ of the Gd2O3:Eu3+ nanorods heat treated at 500˚C, 550˚C, 600˚C, 650˚C and 700˚C (lex = 612 nm and lem = 612 nm)
the XRD patterns and Rietveld refinement and FT-IR analyses indicated the formation of Gd2O3:Eu3+ powders which crystallizes in a cubic structure of crystalline Gd2O3 and space group Ia-3. No secondary phases related to the Eu3+ ions were detected indicating that these ions were incorporated to the hydroxide and oxide matrixes in the analyzed powders. FE-SEM images indicated that the Gd(OH)3:Eu3+ precursor and Gd2O3:Eu3+ powders are composed by several aggregated particles with nanorods-like morphology, which sizes are in the range of 8 and 20 nm. Eu3+ emission and excitation spectra pointed out that the emission in the Gd2O3:Eu3+ powders comes from the energy transfer from the Gd-O and
The authors acknowledge the financial support of the Brazilian research financing institutions: CNPq (INCTMN), CAPES and FAPESP (CEPID). A special thanks for Maria Fernanda Cgnin de Abreu.
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