Kantisara Pita

Influence of annealing atmosphere and temperature on photoluminescence of Tb3+ or Eu3+-activated zinc silicate thin film phosphors via sol–gel method

Abstract Thin films of Zn 2 SiO 4 :Tb 3+ or Eu 3+ were deposited on silicon wafers by a sol–gel method. The films exhibited prominent green or red photoluminescence, due to the sharp and strong intra-4f n -shell electronic transitions. The thermogravimetric analysis curve shows a remarkable weight loss in the temperature range 50–400 ° C , and a slow loss at higher temperature. The increases in fluorescence intensity and decay lifetimes of rare-earth ions sensitive to microstructure and chemical components are attributed to OH removal, nano-crystallite formation and the increased surface roughness by treatment of temperature. Strongly enhanced photoluminescence was observed in samples annealed at 950 °C in a nitrogen atmosphere.

Luminescent properties of rare-earth ion doped yttrium silicate thin film phosphors for a full-colour display

In this paper, we report our results on the sol–gel preparation and spectral properties of (RExY1−x)2SiO5 (RE3+ = Eu3+, Tb3+, Ce3+, x = 0.005, 0.01, 0.02, 0.03 and 0.05) thin films. Effects of annealing temperatures on the thin films structure and optical properties, including luminescence, decay kinetics and CIE colour coordinates have been investigated. Upon exposure to the UV source, films containing Eu3+ and Tb3+ have exhibited bright red- and green-phosphorescent colours, due to the prominent transitions of 5D0→7F2 at 613 nm of Eu3+ and 5D4→7F5 at 543 nm of Tb3+ arising because of the intra-4f n electronic transitions, respectively. The photoluminescence spectrum of (CexY1−x)2SiO5 film mainly shows a broader emission band at 488 nm, which originates from the 5d→4f electron transitions of Ce3+. Luminescence mechanisms of these phosphor thin films have been discussed in detail.

Effects of composition and structure on spectral properties of Eu3+-doped yttrium silicate transparent nanocrystalline films by metallorganic decomposition method

Abstract Transparent thin films of (Eu x Y 1− x ) 2 SiO 5 and (Eu x Y 1− x ) 2 Si 2 O 7 ( x =0.005∼0.05) have been prepared using a metallorganic decomposition sol–gel process. A strong room temperature red emission with predominant wavelength at 614 nm, corresponding to the 5 D 0 → 7 F 2 intra-4f n electric transition of Eu 3+ , has been observed as a function of the annealing temperature. Correlations were observed between optical properties and film structures. As a consequence, a great change in luminescence and CIE coordinates of Eu 3+ -doped Y 2 SiO 5 at high temperature around 1050 °C was attributed to phase transformation of nanocrystalline films. Upon exposure to the UV source, these thin films have shown bright red-phosphorescent color with excellent color saturation.

Surface modified silica mesoporous films as a low dielectric constant intermetal dielectric

Silica mesoporous films with low dielectric constant were successfully fabricated by a multiple-step sol–gel process. Various surface modifications were conducted to make the surface of the films hydrophobicity, which was proved very effective to maintain the low dielectric properties of the films. The basic properties of the silica films were evaluated by atomic force microscopy, specular x-ray reflectivity, Fourier transform infrared, and thermal gravimetric and differential thermal analysis. An inherent low dielectric constant of around 2.0 was realized for about 56% porosity of the silica film with pore size less than 40 nm and the leakage current was at a level of 10−6 A/cm2 after two months of fabrication. Preliminary results of the silica films prepared here present a very positive prospective to intermetal dielectric applications.

The effect of TEOS/MTES ratio on the structural and dielectric properties of porous silica films

This paper presents the results of the characterization of porous silica films used as intermetal dielectrics. The films were fabricated via sol-gel process using tetraethyl orthosilicate (TEOS) and methyltriethoxysilane (MTES) as precursors with acid and base as catalysts. Several advanced techniques such as transmission electron microscopy, specular X-ray reflectivity, Fourier transform infrared spectroscopy, nitrogen adsorption, thermal gravimetric, and differential thermal analysis have been employed to obtain information on the structural properties of the films and reaction mechanisms involved in the sol-gel process of such dielectrics. The characterization results show the effects of the TEOS/MTES ratio on the development of the porosity, pore size, and pore interconnectivity of the films, which reflects the influence of different mechanisms of hydrolysis and condensation of silica precursors in different pH conditions and the existence of covalently bonded organic ligands on the pore structure. An inherently low dielectric constant of around 2.0 was realized for about 60% porosity in the silica films. The pore sizes were less than 10 nm with majority of pores being closed-cells.

Room temperature deposition of p-type arsenic doped ZnO polycrystalline films by laser-assist filtered cathodic vacuum arc technique

The use of combined filtered cathodic vacuum arc (FCVA) technique and laser ablation to fabricate high-quality As doped ZnO (ZnO:As) films at room temperature is proposed. This is possible because FCVA technique is capable of realizing high-quality undoped ZnO films with extremely high resistivity (i.e., extremely low concentration of Zn interstitials) at low deposition temperature. In addition, laser ablation allows the generation of As plume to react with Zn ion species and O2 inside the FCVA chamber to form ZnO:As films. It was shown that high-quality p-type ZnO:As film with a resistivity of 0.05Ωcm, a mobility of 2cm2∕Vs, and a hole concentration of 4×1019cm−3 was obtained at room temperature by using the proposed deposited technique. X-ray photoemission spectroscopy analysis has indicated that complex of As substitutional Zn induces two Zn vacancies (i.e., AsZn–2VZn complex), which is likely to be the defect contributing to the formation of shallow acceptor lever inside the ZnO:As films. Furthermore,...

Synthesis of organically modified mesoporous silica as a low dielectric constant intermetal dielectric

Silica mesoporous films with low dielectric constant were successfully fabricated by a multiple step sol-gel process. The employment of inorganic/organic precursors proved very useful in preventing the film from cracking. The acid/base two-step catalysis could adjust the refractive index or porosity of the silica films effectively and easily. The basic properties of the silica films were evaluated by transmission electron microscopy, specular x-ray reflectivity, Fourier transform infrared spectroscopy, and thermal gravimetric and differential thermal analysis. An inherently low dielectric constant of around 2.0 was realized for about 57% porosity in the silica film with a pore size less than 10 nm. The leakage current was at a level of 10−6 A/cm2 one month after fabrication. The dependencies of the dielectric properties of the films on the relative amount of the components in the starting solution and on the processing temperature were investigated in detail. Preliminary results of the silica films prepar...

Visible red random lasing in Y2O3:Eu3+/ZnO polycrystalline thin films by energy transfer from ZnO films to Eu3+

Visible red random lasing centered at ∼611 nm has been observed in Y2O3:Eu3+/ZnO films at room temperature. Using a 355 nm laser source to excite the ZnO films, ultraviolet (UV) random lasing has been observed. The UV lasing spectrum can be tuned to overlap strongly with the F70-L56 excitation spectrum of Eu3+ ions centered at ∼394 nm by controlling the pump power, leading to very efficient radiative energy transfer from the ZnO films to Eu3+ ions. As a result, a red random lasing centered at ∼611 nm corresponding to the D50-F72 transition of Eu3+ ions was observed.

Defect-induced photoluminescence from tetraethylorthosilicate thin films containing mechanically milled silicon nanocrystals

In this work, the unique synthesis of mechanically milled silicon nanocrystals (Si nc) embedded in tetraethylorthosilicate (TEOS) thin films is reported. A series of Si nc, with sizes ranging from 10to25nm, have been synthesized using mechanical milling. For both the milled Si nc and milled Si nc embedded in TEOS thin film, infrared absorption and photoluminescence results show that the photoluminescence (PL) is not a consequence of quantum confinement, amorphous Si component, or Si–OH or Si–H bonds. The defects, such as nonbridging oxide hole centers (NBOHCs), in amorphous SiO2 are probably the dominant mechanism for the PL of milled Si nc embedded in TEOS thin films. In addition, PL excitation results reveal oxidation-induced strain between the interfaces of milled Si nc∕SiO2 has also generated a new luminescence center. This luminescence center is similar to the NBOHCs attributed to interfacial strain.

Low optical loss germanosilicate planar waveguides by low-pressure inductively coupled plasma-enhanced chemical vapor deposition

This Letter reports on the preparation and properties of germanium-doped silica thin films by a new technique namely inductively coupled plasma-enhanced chemical vapor deposition (ICP-CVD). 13.56 MHz ICP was generated inside the chamber upon the supplying of 1 KW r.f. power at 2.5 Pa. The Films have been deposited on Si-wafers from the tetraethoxysilane, tetramethoxygermane and oxygen system at 400 °C. The behaviors of ∼200 and ∼240 nm UV absorptions under different treatment conditions comprising annealing temperatures and excimer laser exposure have been systematically investigated. A low propagation loss of ∼0.1 dB/cm at 1550 nm has been achieved.