Chu-Chi Ting

Structural evolution and optical properties of TiO2 thin films prepared by thermal oxidation of sputtered Ti films

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 ⩾ 550 °C without going through an anatase-to-rutile transformation. Instead, an additional crystalline Ti2O phase was detected at 550 °C only. An increase in the oxidation temperatures ranging between 700 and 900 °C led to an increase in both the refractive index and absorption coefficient, but a decrease in the band gap energy (Eg). 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.

Preferential growth of thin rutile TiO2 films upon thermal oxidation of sputtered Ti films

Abstract Thin rutile TiO 2 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 TiO 2 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 TiO 2 . However, for the amorphous and low crystalline Ti films, orientation of the crystallites evolved in the resulting TiO 2 film tends to be randomly distributed. The extent of preferential crystal growth of TiO 2 (200) plane can be enhanced by decreasing the annealing temperature or the thickness of Ti film.

Effects of yttrium codoping on photoluminescence of erbium-doped TiO2 films

Er3+–Y3+ codoped TiO2 films were prepared on a fused silica substrate by the sol–gel process. The effect of Y3+ codoping on the ∼1.54 μm 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(∼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.

Comparison of visible fluorescence properties between sol–gel derived Er3+–Yb3+ and Er3+–Y3+ co-doped TiO2 films

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+–Yb3+ co-doped TiO2 system. For Er3+ (5 mol%)–Y3+ co-doped TiO2 samples, the relative intensity ratio (IR/IG) rapidly decreases with the increase of Y3+ concentration above 10 mol%. On the contrary, the relative intensity ratio (IR/IG) 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.

Physical characteristics and infrared fluorescence properties of sol–gel derived Er3+–Yb3+ codoped TiO2

Er3+–Yb3+ codoped TiO2 films were prepared on fused silica by sol–gel processes. The Yb3+ codoping effect on the physical characteristics and ∼1.54 μm photoluminescence (PL) properties of Er3+-doped TiO2 films was investigated. Maximum ∼1.54 μm PL intensity occurs in Er3+ (5 mol %)–Yb3+(30 mol %) codoped TiO2 samples annealed at 700 °C. However, when the concentration of Yb3+ ions is more than 30 mol %, the back energy transfer effect from Er3+ to Yb3+ will deteriorate the ∼1.54 μm 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 %)...

Fluorescence enhancement and structural development of sol–gel derived Er3+-doped SiO2 by yttrium codoping

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 ∼1.54 µm photoluminescence (PL) intensity occurs in the sample with Er3+ (10 mol%)–Y3+ (50 mol%) codoped and annealed at 985 °C. 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 ∼20 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.

P‐79: Engineered Surface with Improved Luminous Efficiency of Phosphor Powder for Plasma Planar Back Light

Simple microwave irradation escalating the luminance efficiency for the commercial phosphor powders is reported. Geometrical variation of the particles from irregular to spherical shape is simultaneously achieved, encouraging an efficient screen-printed phosphor deposition. Particle size reduction following the microwave surface modification gives consdierably improved luminescence efficiecy.

Fluorescence Properties of Sol-gel Derived Er3+-doped TiO2-Al2O3 Composite Thin Films

The photoluminescence (PL) emission from the first excited state (4I13/2) to the ground state (4I15/2) in Er3+ occurs at the wavelength 1.54 µ m, a standard telecommunication wavelength of silica-based optical fibers. Both PL intensity and FWHM spectral width will increase with more Er3+ doping. In the present study, the sol-gel spin coating process was used to prepare the Er3+-doped TiO2-Al2O3 composite thin films. With increasing Al2O3 content, the phase transformation of amorphous to anatase states was delayed in the composite films. The incorporation of Er3+ ions reduces the amount of aluminum sites in the 4-fold coordination and increases the 5-fold coordination. Furthermore, it was found that the PL intensity could be enhanced with the increasing of Al2O3 addition in the Er+3-doped TiO2-Al2O3 composite films.

Structural and Physical Characterization of Erbium-doped TiO2-based Planar Waveguide Amplifiers

The TiO2-Y2O3 systems can offer the densified host matrix with a controllable refractive index ranging from 2.1 to 2.3. Sol-gel method is used to synthesize the erbium-doped TiO2-based Y2O3 precursor solution in this work. It was found that higher Y3+-doped concentration will reduce the refractive index of composite films. When Er2O3 additive was more than 10 mol%, Er3+ ions cluster effect reduced the photoluminescence (PL) intensities in erbium-doped TiO2-Y2O3 films. Furthermore, with increasing Y2O3 addition, an amorphous matrix was formed and enhanced the efficiency of PL.