Search results for "Amorphous solid"
showing 10 items of 622 documents
Structural inhomogeneity of Ge-doped amorphous SiO2 probed by photoluminescence lifetime measurements under synchrotron radiation.
2007
We report a study of the photoluminescence (PL) time decay of the B-type center, characterized by an optical absorption band peaked at similar to 5.2 eV and two related PL bands peaked at similar to 3.2 eV and similar to 4.3 eV, in sol-gel Ge-doped a- SiO2 under excitation by synchrotron radiation. Measurements were carried out by excitation in UV and in vacuum-UV (VUV), and were performed in the temperature range from 8 K up to 300 K in order to isolate the effects of the intersystem-crossing process, proposed to link the two emission bands of the center. Repeating the time decay measurement at several emission energies falling inside the 4.3 eV band, we have observed a variation of the PL…
Luminescence and Raman Detection of Molecular Cl2 and ClClO Molecules in Amorphous SiO2 Matrix
2017
The support from the Latvian Research Program project IMIS 2 (L.S., K.S.) and Latvian Science Council Grant 302/2012 (A.S.) is acknowledged. K.K. was partially supported by the Collaborative Research Project of Materials and Structures Laboratory, Tokyo Institute of Technology. H.H. was supported by the MEXT Element Strategy Initiative to form research cores.
Diffusive equilibrium properties of O2 in amorphous SiO2 nanoparticles probed via dependence of concentration on size and pressure
2014
An experimental study on the diffusive equilibrium value of interstitial O2 in silica nanoparticles was carried out on samples with average particles diameter 40, 14, and 7 nm. The investigation was performed by measuring the concentration of interstitial O2 by Raman and photoluminescence techniques. The dependence of diffusive equilibrium concentration on pressure and temperature was investigated in the pressure range from 0.2 to 76 bar and in the temperature range from 98 to 244 °C. The equilibrium concentration of interstitial O2 follows Henry’s law at pressures below 13 bar whereas a departure from this model is observed at higher pressures. In particular, O2 concentration saturates abo…
Isotope Effect on the Infrared Photoluminescence Decay of Interstitial Oxygen Molecules in Amorphous SiO2
2009
The decay constants of the a1Δg(v=0)→X3Σg-(v=0) infrared photoluminescence (PL) of isotopically-labeled oxygen molecules 16O18O and 18O2 dissolved in the interstitial voids of a-SiO2 are ~1.7 and ~2.5 times larger than that of 16O2. This difference originates from the isotope shift in the energy of the nonradiative transitions from the a state to the vibronic levels of the X ground state. Calibration of the PL quantum yield using the measured decay constants is essential to measure the correct concentration of isotopically-labeled interstitial O2.
The evolution of the fraction of Er ions sensitized by Si nanostructures in silicon-rich silicon oxide thin films
2009
Photoluminescence (PL) and time-resolved PL experiments as a function of the elaboration process are performed on Er-doped silicon-rich silicon oxide (SRO:Er) thin films grown under NH(3) atmosphere. These PL measurements of the Er(3+) emission at 1.54 microm under non-resonant pumping with the Er f-f transitions are obtained for different Er(3+) concentrations, ranging from 0.05 to 1.4 at.%, and various post-growth annealing temperatures of the layers. High resolution transmission electron microscopy (HRTEM) and energy-filtered TEM (EFTEM) analysis show a high density of Si nanostructures composed of amorphous and crystalline nanoclusters varying from 2.7 x 10(18) to 10(18) cm(-3) as a fun…
Exchange between interstitial oxygen molecules and network oxygen atoms in amorphousSiO2studied byO18isotope labeling and infrared photoluminescence …
2011
Amorphous ${\mathrm{SiO}}_{2}$ ($a$-${\mathrm{SiO}}_{2}$) thermally annealed in an oxygen atmosphere incorporates oxygen molecules (O${}_{2}$) in interstitial voids. When the thermal annealing is performed in $^{18}\mathrm{O}$${}_{2}$ gas, interstitial $^{18}\mathrm{O}$${}_{2}$ as well as interstitial $^{16}\mathrm{O}$$^{18}\mathrm{O}$ and $^{16}\mathrm{O}$${}_{2}$ are formed due to the oxygen exchange with the $a$-${\mathrm{SiO}}_{2}$ network. The ${a}^{1}{\ensuremath{\Delta}}_{g}(v=0)\ensuremath{\rightarrow}{X}^{3}{\ensuremath{\Sigma}}_{g}^{\ensuremath{-}}(v=1)$ infrared photoluminescence band of interstitial ${\mathrm{O}}_{2}$ was utilized to quantitatively analyze the oxygen exchange, t…
Tuning of ZnO 1D nanostructures by atomic layer deposition and electrospinning for optical gas sensor applications
2015
We explored for the first time the ability of a three-dimensional polyacrylonitrile/ZnO material—prepared by a combination of electrospinning and atomic layer deposition (ALD) as a new material with a large surface area—to enhance the performance of optical sensors for volatile organic compound (VOC) detection. The photoluminescence (PL) peak intensity of these one-dimensional nanostructures has been enhanced by a factor of 2000 compared to a flat Si substrate. In addition, a phase transition of the ZnO ALD coating from amorphous to crystalline has been observed due to the properties of a polyacrylonitrile nanofiber template: surface strain, roughness, and an increased number of nucleation …
Photoluminescence of Carbon Dots Embedded in a SiO2 Matrix
2016
Abstract We synthetized carbon dots by a pyrolitic method, and studied their photoluminescence in aqueous environment and upon trapping in a solid matrix. To this aim, we devised a facile procedure allowing to embed the dots in amorphous SiO2, without the need of any pre-functionalization of the nanoparticles, and capable of yielding a brightly photoluminescent monolith. Experimental data reveal a remarkable similarity between the emission properties of carbon dots in water and in SiO2, suggesting that the chromophores responsible of the photoluminescence undergo only weak interactions with the environment. Time-resolved photoluminescence data reveal that the typical photoluminescence tunab…
Interstitial O2 distribution in amorphous SiO2 nanoparticles determined by Raman an Photoluminescence spectroscopy
2013
The O2 content and emission properties in silica nanoparticles after thermal treatments in oxygen rich atmosphere have been investigated by Raman and photoluminescence measurements. The nanoparticles have different sizes with average diameter ranging from 7 up to 40 nm. It is found that O2 concentration in nanoparticles monotonically increases with nanoparticles size. This finding is independent on the measurement technique and evidences that oxygen molecules are not present in all the nanoparticles volume. This dependence is interpreted on the basis of a structural model for nanoparticles consisting of a core region able to host the oxygen molecules and a surface shell of fixed size and fr…
Optical properties of ultrathin Al2O3/ZnO nanolaminates
2015
Abstract Because of their high resistance against ultraviolet and high energy particles, ultrathin amorphous nanolaminates can be very attractive for aerospace application. Here we report on the optical and structural properties of ultrathin Al2O3/ZnO nanolaminates deposited by Atomic Layer Deposition. Structural properties of nanolaminates were studied by GIXRD and AFM. Optical characterization was performed by transmittance, spectroscopic ellipsometry and photoluminescence (PL) spectroscopy. Regression analysis of ellipsometric spectra has shown that absorption peak decreases and blue shifted with the decrease of bilayer thickness in the stack. On the basis of the analysis of structural a…