Hong Zhanglian

Synthesis in situ of 2,2′-dipyridyl-Tb(iii) complexes in silica gel

Abstracts are not published in this journal

Structural evolution and fluorescence properties of Tb3+-doped silica xerogels in the gel to glass conversion

The Tb3+-doped silica glasses were prepared by a sol-gel process with appropriate heat treatment. The structural changes during the gel to glass transition of Tb3+-doped silica xerogels and the effect on fluorescence properties of Tb3+ were studied in this paper. The results show that the doped silica glasses may be obtained after the xerogels are heat-treated at 800 °C for 24 h. During heat treatment at 400 °C, the residual organic molecules and most of the absorbed water molecules in silica xerogels are removed, and the SiO4 tetrahedral structural network forms and strengthens gradually with decreasing number of silanol (SiOH) groups. The fluorescence intensity of Tb3+ ions increases remarkably when the doped xerogel is heat-treated in the range 300–500 °C, and increases slowly above 500 °C(up to 800 °C). This observation leads to a conclusion that the radiative transitions of Tb3+ ion in the aqueous gels are quenched strongly by the high-frequency vibrations of OH groups from the coordinated water rather than physically absorbed water. The inhomogeneity in the site state of Tb3+ ions increases with rise in temperature of heat treatment, which broadens the emission bands of Tb3+ ions doped in silica glasses. Moreover, there will also be an additional interaction owing to the influence of the ligand field of the glasses, which makes the emission bands shift to red and produces Stark splitting of the Tb3+ ion energy levels.

Preparation and Luminescence Properties of Y2O3: Eu3+ Nanorods via Post Annealing Process

Abstract Yttrium oxide doped with europium has a great prospective for FED and PDP phosphor application. In present study, the precursor of yttrium oxide hydroxide nitrate nanorod, which was prepared via hydrothermal reaction route using PEG-6000 as template from the starting Y(NO 3 ) 3 and KOH reactant system, was used to prepare Y 2 O 3 :Eu 3+ nanorod via a post annealing process during which the precursor with adjustable shape and size was transformed to final Y 2 O 3 : Eu 3+ product. XRD, field emission scanning electron microscopy (FE-SEM) and photoluminescence spectra (PL) were used to characterize the crystalline, morphology and luminescence properties of as-formed Y 2 O 3 : Eu 3+ products synthesized at different post annealing temperatures, respectively. The results indicate that grain morphology of obtained Y 2 O 3 : Eu 3+ product was nanorod with a mean diameter of about 40 ∼ 60 nm and length of about 500 ∼ 700 nm, the nanorod structure and morphology of obtained Y 2 O 3 : Eu 3+ product maintained during post annealing process and the size varied slightly with different annealing temperatures. Pure cubic Y 2 O 3 : Eu 3+ phase was formed and the size was the smallest at annealing treatment of 500 °C. Under the annealing temperature below 500 °C its diameter increased with increasing annealing temperature, and remained in a stable size when the annealing temperature was above 500 °C. The PL spectra of excitation spectra of Y 2 O 3 : Eu 3+ product show that it exhibits excitation band located at about 395 and 468 nm, respectively. Above two excitation bands could be ascribed to the transition 4f-4f of Eu 3+ ions in the Y 2 O 3 host. On the other hand, the main emission peaks of the as-prepared products could be ascribed to the Eu 3+ ions transition from 5 D 0 to 7 F 2 . Furthermore, the luminescent intensity was improved about three times when the annealing temperature increased from 500 to 1000 °C.

Synthesis of Yttrium Oxide Nanocrystal via Solvothermal Process

Abstract Y 2 O 3 nanomaterials have been widely used in transparent ceramics and luminescent devices. Recently there are many studies focusing on controlling the size and morphology of Y 2 O 3 in order to obtain better materials performance. In present study, yttrium oxyhydroxide precursor was synthesized via a facile solvothermal process through the dissolution-recrystallization mechanism of Y 2 O 3 raw powders in the ethylenediamine solvent, then nanosized yttrium oxide crystal was prepared from the precursor through post heat treatment process. The effects of solvothermal treatment temperature, holding time, solvent kinds and post heat treatment parameters on crystalline structure, grain shape and size of nanocrystal were investigated by XRD, TEM and TGA-DTA measurements. TEM images reveal that the morphology of product after post heat treatment at 460 °C for 12 h is rice-like nanocrystal. XRD shows that this product is pure cubic Y 2 O 3 cphase. Present study reveals that high purity Y 2 O 3 with rice-like morphology can be easily prepared with average size around 30 nm under suitable post heat treatment parameters. In addition the effects of solvents such as water and ethanol etc. on the crystal structure and morphology were also investigated. It is suggested that dissolution-recrystallization process may be the main mechanism for the formation of nano-sized YOOH precursors under solvothermal reaction condition, and the ethylenediamine solvent is likely to play an important role in controlling the transformation process of yttria precursors to the Y 2 O 3 nanocrystal.

The influence of the matrix on the fluorescence properties of pyrene

The fluorescence properties of pyrene doped in silica xerogels by a sol-gel process and dissolved in ethanol in various concentrations were studied comparatively. With increasing gelation time the fluorescence spectra of pyrene doped in silica gels change greatly. Pyrene monomer excitation bands arise gradually with decreasing intensity of pyrene excimer excitation bands, which increases the intensity of the monomer emission and decreases that of the excimer emission. Compared with dissolving pyrene in ethanol, doping with pyrene in silica xerogels can increase the quenching concentration of pyrene enormously and thus increase the monomer fluorescence intensity of pyrene by a factor of approximately 20 with respect to that in ethanol solution. These changes can be explained by the modification of the pyrene surroundings. The pyrene molecules are isolated and absorbed in the tiny pores of the silica network steadily to avoid aggregate formation in silica xerogels.

Luminescence Characterization of Mg Doped Y2O2S:Ti Long Afterglow Phosphor

Abstract Y 1.94- x Mg x O 2 S:0.06Ti (0≤ x ≤0.10) phosphors with long afterglow were synthesized by solid state reaction route. The photoluminescence spectra, decay curves, thermoluminescent spectra and chromaticity coordinate curves were investigated. The results show that the luminescence intensity of Y 1.94- x Mg x O 2 S:0.06Ti (0≤ x ≤0.10) phosphors decrease gradually with increasing Mg 2+ ion content, and the shape of luminescence spectra and chromaticity coordinate change as well. Furthermore, two thermoluminescent peaks in single Ti-doped Y 2 O 2 S sample are found at 91.8 and 221.5 °C, respectively. Nevertheless, significant different spectra were found for the Mg, Ti co-doped Y 2 O 2 S samples that three thermoluminescence peaks appear at 52.3, 141.7 and 226.8 °C, respectively. These results indicate that the co-doped Mg ion changes the inherent trap depth of single Ti-doped Y 2 O 2 S: Ti phosphor, and induces simultaneously a new trap level in the Y 1.94- x Mg x O 2 S:0.06Ti phosphor. Based on the analysis of thermoluminescent spectra, photoluminescent spectra, decay curve and crystal structure defect, it was proposed that the varied structure defect and introduced new trap level by the doped Mg 2+ ions should be responsible for reducing luminescence intensity and varying color in the Y 1.94- x Mg x O 2 S:0.06Ti phosphor.