Browsing by Author "Ting, CC"

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Comparison of visible fluorescence properties between sol-gel derived Er3+-Yb3+ and Er3+-Y3+ co-doped TiO2 films
(2003-06-23)
Chen, SY
;
Ting, CC
;
Hsieh, WF
;
材料科學與工程學系
;
光電工程學系
Both Er3+-Yb3+ and Er3+-Y3+ co-doped TiO2 films were prepared on fused silica by sol-gel processes. The effect of doping concentration upon the up-conversion fluorescence of Yb3+-Er3+ and Er3+-Y3+ co-doped TiO2 systems will be focused in this investigation. Although the influence of Yb3+ and Y3+ ions on the structural of Er3+-TiO2 host material is almost the same, different up-conversion emissions are observed. Both Er3+-doped and Er3+-Y3+ co-doped TiO2 films exhibit the up-conversion emission with green and red light. However, much stronger intensity of red light relative to green light is observed for the Er3+-Y3+ co-doped TiO2 system. For Er3+ (5 mol%)-Y3+ co-doped TiO2 samples, the relative intensity ratio (I-R/I-G) rapidly decreases with the increase of Y3+ concentration above 10 mol%. On the contrary, the relative intensity ratio (I-R/I-G) increases with increasing Yb3+ concentration for Er3+(5 mol%)-Yb3+ co-doped TiO2 samples. The up-conversion emission in the Er3+-Y3+ co-doped TiO2 system belongs to a two-photon absorption up-conversion process. However, the overall up-conversion efficiency in the Er3+-Yb3+ co-doped TiO2 system could be contributed from the complicated mechanisms. (C) 2003 Elsevier Science B.V. All rights reserved.
Effects of yttrium codoping on photoluminescence of erbium-doped TiO2 films
(2001-12-01)
Ting, CC
;
Chen, SY
;
Hsieh, WF
;
Lee, HY
;
材料科學與工程學系
Er3+-Y3+ codoped TiO2 films were prepared on a fused silica substrate by the sol-gel process. The effect of Y3+ codoping on the similar to1.54 mum photoluminescence (PL) properties of Er3+-doped TiO2 films are investigated. Enhancement of PL properties due to Y3+ codoping by a factor of 10 for intensity and of 1.5 for the full width at half maximum in comparison with the Er3+-Al3+ codoped SiO2 system has been observed in the film annealed at Er3+:Y3+:Ti4+=5:30(similar to 50):100. Extended x-ray absorption fine structure measurements show that the local chemical environment of Er3+ ions in the Er3+-Y3+ codoped TiO2 films is similar to that in Er2O3. The average spatial distance between Er3+ ions is enlarged due to the partial substitution of Y3+ for Er3+ ions in the Er2O3-like local structure. It is believed that the more intense PL emission of the Er3+-Y3+ codoped TiO2 films can be attributed to the better dispersion and distorted local structure of Er3+ ions in the TiO2 host matrix by yttrium codoping. (C) 2001 American Institute of Physics.
Fluorescence enhancement and structural development of sol-gel derived Er3+-doped SiO2 by yttrium codoping
(2002)
Chen, SY
;
Ting, CC
;
Li, CH
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材料科學與工程學系
;
Department of Materials Science and Engineering
Er3+-Y3+ codoped SiO2 powdered bulks were prepared by a sol-gel process. The effect of Y3+ codoping on the fluorescence properties and structural development of Er3+-doped SiO2 is investigated. The maximum similar to1.54 mum photoluminescence (PL) intensity occurs in the sample with Er3+ (10 mol%)-Y3+ (50 mol%) codoped and annealed at 985 degreesC. This can be attributed to the competition between the content of hydroxy groups and Er site symmetry. Improvement of optimum PL properties due to Y3+ codoping by a factor of similar to20 for intensity and 1.8 for the full width at half maximum (57 nm) was obtained in comparison with the Er3+-doped SiO2 system. Extended X-ray absorption fine structure analysis shows that the local chemical environment of Er3+ ions in the Er3+-Y3+ codoped SiO2 is similar to that in Er2O3. The average spatial distance between Er3+ ions is enlarged due to a partial substitution of Y3+ for Er3+ ions in the Er2O3-like local structure, which results in a reduction of the concentration quenching effect.
Influence of ligand groups in Ti precursors on phase transformation and microstructural evolution of TiO2 thin films prepared by the wet chemical process
(2001-06-01)
Ting, CC
;
Chen, SY
;
材料科學與工程學系
;
Department of Materials Science and Engineering
TiO2 thin films prepared by metalorganic decomposition (MOD-TIO,) and sol-gel processes (SG-TiO2) were investigated in terms of the anatase-to-rutile phase transformation and microstructural evolution. It was found that the chemical reactivity of the ligand groups initially coordinated on the titanium precursor plays a decisive role in the structure development of as-deposited SG- and MOD-TiO2 films. MOD-TiO2 films consist of small aggregated particles and therefore, tend to coalesce together to form an inhomogeneous microstructure during the anatase-to-rutile phase transformation. On the other hand, SG-TiO2 films consist of uniform large particles that tend to grow homogeneously. MOD-TiO2 films showed a higher crystallization temperature than the SG-TiO2 films but the temperature of the anatase-to-rutile phase transformation is much lower in MOD- (approximately 775 degreesC) as compared to SG-TIO, films (approximately 930 degreesC). The activation energy (Q) was estimated as 524 and 882 kJ/mol for the MOD- and SG-TIO, films, respectively, The lower transformation temperature and activation energy in MOD-TiO2 films were due to smaller grain size and more potential nucleation sites existing in the un-transformed MOD-TiO2 film structure, which can accelerate the rate of anatase-to-rutile transformation.
Physical characteristics and infrared fluorescence properties of sol-gel derived Er3+-Yb3+ codoped TiO2
(2003-08-01)
Ting, CC
;
Chen, SY
;
Lee, HY
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Er3+-Yb3+ codoped TiO2 films were prepared on fused silica by sol-gel processes. The Yb3+ codoping effect on the physical characteristics and similar to1.54 mum photoluminescence (PL) properties of Er3+-doped TiO2 films was investigated. Maximum similar to1.54 mum PL intensity occurs in Er3+ (5 mol %)-Yb-3+ (30 mol %) codoped TiO2 samples annealed at 700degreesC. However, when the concentration of Yb3+ ions is more than 30 mol %, the back energy transfer effect from Er3+ to Yb3+ will deteriorate the similar to1.54 mum PL efficiency. Extended x-ray absorption fine structure measurements show that the average spatial distance between Er3+ ions is slightly decreased due to the partial substitution of Yb3+ for Er3+ ions in the local structure. The Yb3+ ion in the Er3+-Yb3+ codoped TiO2 samples not only plays the role of disperser but is also a sensitizer of the Er3+ ion. This dual effect leads to larger PL intensity in the Er3+-Yb3+ codoped TiO2 system in comparison with Er3+-Y3+ codoped TiO2 samples. Compared with SiO2 films with Er3+ (5 mol%)-Yb3+ (30 mol %) codoped and annealed at optimal temperature of 985degreesC, the Er3+ -Yb3+ codoped TiO2 film obtains better PL properties at lower annealing temperature. (C) 2003 American Institute of Physics.
Preferential growth of thin rutile TiO2 films upon thermal oxidation of sputtered Ti films
(2002-01-01)
Ting, CC
;
Chen, SY
;
Liu, DM
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Thin rutile TiO2 films with (200) preferred orientation were fabricated by thermal oxidation of sputtered Ti metal films on a fused silica substrate. Experimental results indicate that the preferential crystal growth of (200)-oriented TiO2 is determined by the competition between surface free energy and strain energy. The highly crystalline Ti film with (002) orientation has a greater tendency to promote the growth of (200)-oriented TiO2 However, for the amorphous and low crystalline Ti films, orientation of the crystallites evolved in the resulting TiO2, film tends to be randomly distributed. The extent of preferential crystal growth of TiO2 (200) plane can be enhanced by decreasing the annealing temperature or the thickness of Ti film. (C) 2002 Elsevier Science B.V All rights reserved.
Structural evolution and optical properties of TiO2 thin films prepared by thermal oxidation of sputtered Ti films
(2000-10-15)
Ting, CC
;
Chen, SY
;
Liu, DM
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A dense rutile TiO2 thin film was synthesized by the thermal oxidation of a sputtered titanium metal film in ambient air. The effects on optical properties of TiO2 films of the crystal structure and microstructural evolution at various oxidation temperatures were investigated. The Ti films transformed into single-phase rutile TiO2 at temperatures greater than or equal to 550 degrees C without going through an anatase-to-rutile transformation. Instead, an additional crystalline Ti2O phase was detected at 550 degrees C only. An increase in the oxidation temperatures ranging between 700 and 900 degrees C led to an increase in both the refractive index and absorption coefficient, but a decrease in the band gap energy (E-g). According to the coherent potential approximation model, the band gap evolution of the oxidized films was primarily attributed to the electronic disorder due to oxygen deficiency at a higher oxidation temperature rather than the presence of an amorphous component in the prepared films. (C) 2000 American Institute of Physics. [S0021-8979(00)07920-2].