Local modification of Eu3+ ions doped in SnO2- and Al2O3-SiO2 glasses was investigated using a femtosecond laser pulse. SnO2 nanocrystals were successfully precipitated in transparent glasses by irradiation with an 800-nm femtosecond laser. Upon laser irradiation, the Sn atoms were activated to react with oxygen, resulting in the formation of SnO2 nanocrystals. The precipitated SnO2 crystals grew up to ca. 5 nm size by the Joule-heating effect of the laser. The fluorescence intensities of the codoped-Eu3+ ions were enhanced higher than 100 times that of the glass without nanocrystals by exciting with the energy corresponding to the absorption edge of the SnO2 nanocrystals, the energy of which is effectively transferred to the Eu3+ ions. Near-infrared to visible up-converted fluorescence was observed in the Eu+3 ions doped in the Al2O3-SiO2 glasses during femtosecond laser irradiation. The dependence of the intensity of the Eu3+-emission on the pump power reveals that the three-photon excitation is dominant in the up-conversion process. These glasses can provide a bright prospect for their optical applications.
The persistent spectral hole-burning phenomenon was investigated for Sm2+ ions-doped Al2O3-SiO2 glasses prepared by the sol-gel method. The efficiency of hole-burning, burned at low temperature ~77K, was proportionally increased with the content of OH groups surrounding the rare-earth ions. The proposed mechanism for hole-burning was the optically activated rearrangement of the OH bonds surrounding the rare-earth ions. The burned-hole was thermally refilled and erased above ~200 K. On the other hand, the glasses obtained by heating in H2 gas or irradiating with x-rays showed PSHB up to room temperature. When heated in H2 gas, the H2 molecules react with oxygen ions to form H2O. Removal of the generated H2O causes the number of oxygen ions surrounding rare-earth ions to decrease, resulting into the reduction of the ions. The hole burning in the H2-treated glasses was performed by the electron transfer between the rare-earth ions and the trapping centers. In contrast, in the x-ray irradiated glass, it was concluded that the rear-earth ions are deuced into the divalent state by electron transfer from the oxygen defect center. The hole defect centers are trapped in oxygen ions bound with Al3+ ions. The spectral hole burning of the x-ray irradiated glasses could be burned by the reverse reaction of the reduction of the rare-earth ions. A short distance between the Sm2+ and oxygen defect centers brought a high-speed hole burning, that is, 30 times faster than in a similar H2 gas treated glass.
Dynamical Faraday rotation measurements with pulsed magnetic fields up to ~16 T have been carried out to investigate magnetic interactions between Tb3+ ions in highly Tb2O3-concentrated borate glasses (25-40mol%). These glasses were completely paramagnetic around room temperature, while a cooling down below 100 K began to produce antiferro-couplings of magnetic moments (J = 6) of Tb3+ ions in local areas of the glasses due to the superexchange interactions via oxygen atoms. The modification of the magnetic structure by doping with divalent manganese ions increased the magnetic correlation temperature. It will be also given that a novel glass matrix of 5B2O3-3Ga2O3-3SiO2-P2O5 has been developed in order to increase Tb2O3 content up to 40 mol.% in glasses.
Al2O3-SiO2 glasses doped with Sm3+ ions were prepared using sol-gel method, in which the Sm3+ ions were reduced into Sm2+ by heaing in H2-gas or irradiating with x-ray. When heated in H2 gas, the H2 molecules react with oxygen ions to form H2O. Removal of the generated H2O causes the number of oxygen ions surrounding Sm3+ to decrease, resulting into the resuction of the Sm3+ ions. in contrast, in the x-ray irradiated glass, it is concluded that the Sm3+ ions are reduced into Sm2+ by electron transfer from the oxygen defect center. The hole defect centers are trapped in oxygen ions boound with Al3+ ions. The spectral hole burning of the x-ray irradiated glasses could be burned by the reverse reaction of the reduction of Sm3+ ions, that is, the electron transfer from the excited Sm2+ into the surrounding oxygen. A short distance between the Sm2+ and oxygen defect centers brings fast hole burning. On the other hand, the hole burning in the H2-treated glasses was performed by the electron transfer between the Sm2+ and the trapping center such as Sm3+.
Persistent spectral hole burning (PSHB) spectra were observed at room temperature in Eu3+ ions-doped glasses treated with either H2 gas or X-ray. The Eu3+-doped Al2O3-SiO2 glasses were prepare by sol-gel process. The glasses were heated at 500 to 800 degrees C in H2 gas, and irradiated with x-ray. The PSHB spectra were burned on the 7F0 yields 5D0 transition of the Eu3+ ions. The hole depth increased with increasing heat treatment time and is maximum for the samples heated at 600 degrees C for 1h. In the x-ray-irradiated glasses, the PSHB spectra were observed at room temperature for the first time, to our knowledge, and the hole depth increases with increasing irradiation time. In the x-ray-irradiated glasses, no fluorescence was observed form the Eu3+ ions. A novel. Model for hole burning is proposed on the basis of the excitation of the Eu3+ ions and subsequent hole trapping in the oxygen- defect centers of the Al-O polyhedra.
Recently, we have successfully incorporated gold nanoclusters into silica matrix by a sol-gel technique, where the synthesis of gold clusters was conducted in presence of PVP. In this paper, we report linear and nonlinear optical properties of the polymer-blocked gold clusters in silica matrix. The Au/SiO2 glass were characterized by transverse electron microscopy (TEM), x-ray diffraction (XRD), and Mie-Drude analysis of linear absorption spectra. The hydrophilic polymer, exhibiting the strong metal-polymer interaction which stemmed from the lone pair from the nitrogen with the metal particles, prohibited the flocculation and growth of gold clusters in gel-glass transition. The degenerate four-wave mixing experiment was performed to obtain the nonlinear susceptibility (chi) (3), which was evaluated to be 1.7 X 10-9 esu, in consistent with a theoretical value expected from hot electron contribution.
Room temperature persistent spectral hole burning (PSHB) was observed in Sm2+ and Eu3+-doped Al2O3- SiO2 glasses prepared by a sol-gel method. The glasses were obtained by heating the gels in hydrogen gas and the spectral hole was burned in the excitation spectrum of the 7F0 yields 5D0 transition of the Sm2+ and Eu3+ ions. The depth of the hole burned at 77 K decreased with increasing the cycling temperature. The decrease in the hole-depth is due to the thermal relaxation of the burnt-state of OH bonds surrounding the rare-earth ions. The depth of hole burned in the Sm2+-doped glass heated in 20 percent H2-80 percent N2 gas exhibited the PSHB at room temperature. We considered that the electron transfer between the rare-earth ions and the Al-related defect centers acts for hole burning.
We demonstrate a sol-gel method for preparing Eu3+ and Sm2+ ions-doped glasses exhibiting persistent spectral hole burning at high temperature. Glasses having the composition of Eu3+ or Sm2+-doped Al2O3-SiO2 have been prepared by the hydrolysis of metal alkoxides and heating at 800 degree(s)C in air or hydrogen gas atmosphere, respectively. The persistent spectral hole burning is measured within the 7F0-5D0 transition band. For the glasses containing OH bonds, the hole is formed by the photoinduced rearrangement of the OH bonds surrounding the Eu3+ or Sm2+ ions, and is thermally refilled and erased above approximately 200 K. On the other hand, the glasses heated in hydrogen gas show the hole spectra above approximately 200 K. The hole depth is independent of the temperature and is approximately 7 and 15% of the total intensity at room temperature for the Eu3+ and Sm2+ ions-doped glasses, respectively. The proposed mechanism is the electron transfer between the rare-earth ions and the defect centers related with Al3+ ions in glass network.
Sm2+-doped glasses in the system of Al2O3-SiO2 were prepared by the sol-gel processing of metal alkoxides and the reaction with H2 gas at 800 degrees Celsius, of which hole burning properties were investigated. Sm3+ ions-containing glasses prepared by a sol-gel method were reacted with H2 gas to form the Sm2+ ions. Fluorescence line narrowing spectra of the 5D0 yields 7F1 transition were analyzed to study the local structure surrounding the Sm2+ ion. It is concluded that the Sm2+ ions are closely coordinated with nine oxygens of the AlO6 group in aluminosilicate glasses and the addition of Al3+ ions into glass induces an increase in the coordination number of the Sm2+. The fluorescence intensity of the Sm2+ and Sm3+ ions considerably increases in glasses containing more than 5 mol% Al2O3. The holes were burned in the 7F0 yields 5D0 line of the Sm2+ ions using a DCM dye laser at 77 K. The hole depth increased with increasing the laser irradiation time, reaching up to approximately 15% of the total intensity within a few hundred seconds. The hole width was 3 cm-1 full width at half maximum at 77 K and increased with increasing temperature.
Ge nanocrystal-embedded SiO2 glasses were successfully prepared by a sol-gel process. The glasses synthesized through hydrolysis of Si(OC2H5)4 and GeCl4 were heated in the presence of hydrogen at 400 to 700 degree(s)C, in which Ge4+ ions were reduced to precipitate nanosized Ge crystals. Glasses doped with Ge nanocrystals of a diameter of approximately 5 nm showed the optical absorption edge at approximately 2.5 eV and a strong room temperature photoluminescence with peaks at 2.35, 2.15 eV and weak at 1.85 eV. Large Ge crystals precipitated by heating above 800 degree(s)C showed no photoluminescence.
We have successfully incorporated Sm2+ ions into alumino-silicate glasses using a sol-gel method. The gels synthesized through hydrolysis of Si(OC2H5)4, Al(OC4H9)3, and SmCl3(DOT)6H2O were heated in air, followed by heating in the presence of hydrogen, in which samarium ions were reduced from the trivalent to divalent state. Glasses incorporated with Sm2+ showed an intense emission with peaks at 683, 700, and 725 nm due to 5D0 yields 7F0,1,2 transitions, respectively, of the Sm2+ ions. Decay time was estimated to be 0.6 msec.
Microcrystalline CdTe-doped glasses were prepared by heating the gels in H2-N2 atmosphere. When heated in H2-N2 gas, Te ions were reduced into Te2-, which reacted with Cd2+, ions to form CdTe crystals. The size of CdTe crystals was about 3.5 nm in radius, which was controlled by changing the conditions of gel synthesis. The optical absorption edge energies were reciprocally proportional to the square of the crystal radius.
The sol-gel process has been applied successfully to the preparation of small-particle-size ZnS, CdS
or PbS-doped silica glasses with a significant quantum size effect. Gels prepared through the
hydrolysis of complex solutions of Si(0C2H5)4 and acetate of Zn, Cd or Pb were heated at 500 to 900°C,
then reacted with H2S gas to form fine microcrystals doped glasses. From X-ray diffraction analyses
and transmission electron mlcrographs, these crystals were cubic ZnS, hexagonal CdS and cubic PbS
crystal, respectively, and their sizes were 2 to 8 nm in diameter. In the optical absorption spectra, the
absorption edge exhibited a blue shift compared with those of the bulk sulfides crystals. Size
dependence of energy shift was discussed in relation to size quantization of electron-hole in
microcrystals. The nonlinearity was estimated to be 1.5 x i0O esu for 2% CdS doped glass.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.