Wang Minquan

Luminescence of Bi3+ ions and energy transfer from Bi3+ ions to Eu3+ ions in silica glasses prepared by the sol-gel process

Abstract Luminescence of Bi3+ ions and energy transfer from Bi3+ ions to Eu3+ ions in silica glasses prepared by the sol-gel process have been investigated. The results showed that the excitation band of Bi3+ ions corresponds to the 1 S 0 → 1 P 1 transition and emission spectra consists of a single broad band without structure centred at 395 nm, which corresponds to 3 P 1 → 1 S 0 transition. When a small amount of Bi3+ ions was introduced to 1 mol% Eu3+ ions the doped silica gel glass emission intensity of Eu3+ ions got significantly stronger, which suggests very efficient energy transfer from Bi3+ ions to Eu3+ ions. It can be assigned to significant energy overlap between the emission band of the Bi3+ ion and the excitation band of the Eu3+ ion. However, due to a larger energy overlap between emission and excitation bands of Bi3+, when Bi3+ ion concentration in silica gel glasses was more than 0.5 mol% the probability of energy transfer between Bi3+ ions increased rapidly and the probability of energy transfer from Bi3+ ions to Eu3+ ions decreased relatively. As a consequence, the sensitized effectiveness of the Bi3+ ion on the emission spectrum of the Eu3+ ion drastically decreased with increasing Bi3+ ion concentration.

Research on fluorescence spectra and structure of single-phase 4SrO.7Al2O3 :Eu2+ phosphor prepared by solid-state reaction method

In the view of material physical chemistry, the solid-state reaction process and phase-forming rule of 4SrO·7Al2O3 have been studied. It is verified that 3SrO·Al2O3 which is rich in strontium is formed firstly at ≈1000°C, and with the calcining temperature going up to 1300°C gradually, aluminates rich in strontium change to the rich in aluminum in turn. In other words, strontium aluminates are found in the order from 3SrO·Al2O3, SrO·Al2O3 to 4SrO·7Al2O3 and SrO·6Al2O3, and the aluminate is 4SrO·7Al2O3, which exists steadily at 1300°C. The synthesis conditions of single-phase 4SrO·7Al2O3 are determined, and the data of X-ray powder diffraction and lattice structure of 4SrO·7Al2O3, which crystallizes in the orthorhombic Pmma space group with a=24.765A, b=8.478A and c=4.882A are presented. Also the differences of fluorescence spectrum between phosphor 4SrO·7Al2O3:Eu2+ and phosphor SrO·Al2O3:Eu2+are discussed. And the reliable basis is provided for the synthesis and determination of the new blue–green phosphor 4SrO·7Al2O3:Eu2+ with high efficiency.

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 fluorescence properties of nanocomposites of amorphous silica glasses doped with lanthanide(III) benzoates

Abstract Lanthanide(III) benzoate complexes are decomposed by a few drops of HCl and, thus, cannot be doped in amorphous silica glasses prepared by the acidic (HCl) hydrolysis of tetraethoxysilane (TEOS). This work presents a novel technique of homogeneous doping these complexes in silica gel glasses. Eu(III) (or Tb(III)) and benzoic acid are co-introduced in sol-gel precursor solutions with suitable pH. The nano-scale Eu(III) (or Tb(III)) benzoate complexes are confirmed to form in amorphous silica glass through controlled gelation and drying. The fluorescence spectra of Eu(III) (or Tb(III)) in nanocomposites and the energy transfer efficiencies between Eu(III) (or Tb(III)) and benzoate are studied.

In situ synthesis and fluorescence characterization of 2,2′-dipyridyl-Eu(III) complex in silica xerogel prepared by the sol-gel process

Abstract The complex of Eu(III) with 2,2′-dipyridyl is decomposed by water, and thus cannot be doped in gel glasses prepared by the sol-gel process. This paper presents a novel technique of homogeneous doping of the 2,2′-dipyridyl-Eu(III) complex in silica gel glass. By codoping of 2,2′-dipyridyl and Eu(III) in silica xerogel, an in situ complex of Eu(III) with 2,2′-dipyridyl is synthesized in the transparent monolithic gel glass by suitable heat treatment. Compared with a sample undergoing no heat treatment, the fluorescence intensity of Eu(III) in the xenogel heated at 100°C for 24 h increases by a factor of about ten due to the formation of the in situ 2,2′-dipyridyl-Eu(III) complex. From the fluorescence spectrum, it is suggested that the in situ complex may be Eu(C 10 H 8 N 2 )Cl 3 ·4H 2 O.

Tunable Solid-State Dye Laser with Narrow Linewidth Operation

Tunable radiation with a linewidth of 0.014?nm was obtained in Rhodamine?B, Rhodamine?6G, Perylene orange and Pyrromethene?567-doped GPTMS solid-state dye materials using intracavity grating dispersive oscillation. The solid dye samples were specially designed in the way in which they are gelling, drying and ageing between two anti-reflection coated disks, thus without any mechanical and optical processing. The conversion efficiency of 4.6% and the tunable range of 40?nm from 589-629?nm have been achieved in Rhodamine?B-doped samples. The broadband lasing of 4.4?nm and 54% slope efficiency were also demonstrated in the experiment.

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.

Dimerization of zinc tetrasulfophthalocyanine in sol–gel process

Abstract The issue of dimerization is vital in determining the optical properties of dye-doped sol–gel materials and metallophthalocyanine offers an excellent opportunity to characterize dimmers from monomers because of their identified absorption bands. In this paper, zinc tetrasulfophthalocyanine (ZnTSPc) was encapsulated in silica–xerogel matrix by sol–gel technique. Dimerization of ZnTSPc was studied using UV–Vis optical absorption spectra, correlated with various stages of the sol–gel process. The results show that in the composites ZnTSPc concurrence in forms of monomer and dimmer, and dimerization behaves differently in the sol, gel and xerogel stages. Reasons are given from the change of the microenvironment of the composites in which ZnTSPc existed.

Encapsulation of aromatic oxygen palladium phthalocyanine in silica xerogel and its optical limiting property

Abstract Metallophthalocyanines (MPc) exhibit, among many useful properties, the ability to protect sensors against short, intense pulse deleterious to efficient sensor operation. For the successful application of this optical limiting property, an important issue is the incorporation of MPc molecules in a matrix to fabricate a solid state system. We report here the study of different concentrations of aromatic oxygen palladium phthalocyanine (ArOPdPc) encapsulated in silica xerogel obtained by the sol–gel technique. The resulted composites were transparent and homogeneous with the required optical limiting properties. The trapping effect was confirmed by the characteristic absorption bands of ArOPcPd in the UV–Vis spectra. The optical limiting properties of the composites were measured at 532 nm with 8 ns pulses. The results showed that the composites had obviously optical limiting effect, owing to the existing of large amount of monomers and the introduction of palladium atom in the cavity of phthalocyanine ring.