Optical Phonons in SiO2 Sol–Gel Derived Colored Glasses Doped with Cu and Fe

Abstract

Optical phonons in SiO2 samples prepared by the sol‐gel method and colored by doping with Fe and Cu were studied using X‐ray diffraction, electron spin resonance and infrared spectroscopy. The vibration modes in pure and Cu‐ or Fe‐doped glasses are investigated as a function of doping concentration and annealing temperature. It is found that the heat treatments in air atmosphere have a remarkable influence on the width of the stretching absorption bands related to the asymmetric vibrations in the SiO2 matrix. A simple description of the different types of vibration modes in the quasilinear Si–O–Si chain is given and correlated with the characteristics of the phonon bands observed. A relation between the bandwidth of these modes and the change in the phonon scattering rate caused by the Cu or Fe doping is established. Based on this model, the percentage of Cu incorporated on the Si sites into SiO2 matrix was calculated. The behavior of the vibration spectra in Fe‐doped glasses is different and it indicates less incorporation of this element into the SiO2 matrix.

Raman study of copper and iron oxide particles embedded in an SiO2 matrix

“…This result agrees with other reports. 5,22 The air oxidation of metallic copper has been reported before and the results are similar to those reported here, in the sense that heat treatment for 1 h at about 300°C produces the formation of copper oxides, with no prior phase formation. 29 In the sol-gel samples, higher annealing temperatures are needed to obtain these oxides and at certain treatment temperatures and copper concentrations a copper silicate is formed.…”

“…This band is associated with the symmetric A 1 bond stretching mode of [NO 3 ] ž radicals forming copper nitrate particles; this could indicate that some of the copper is still present in the form of nitrate. 22 The last statement above is also supported by the xray diffraction data for the same samples whose Raman spectra are similar to that shown in Fig. 1.…”

Structure of heat-treated sol-gel SiO2 glasses containing silver

“…In samples heat treated at 300°C, the nitrate is decomposed. Then most of the nitrogen evolves in the form of nitrogen oxides, 12 and the XRD pattern shows only weak diffraction lines identified with the silver nitrite (AgNO 2 , number 4). In this pattern, the broad band due to the amorphous SiO 2 is still present.…”

Investigation of metal-induced low-temperature crystallization of SiO/sub 2/ sol-gel glass containing Ag

“…This structure is achieved in bulk samples prepared from starting solution with an enhanced hydrolysis. Our previous data [5,6] show that the powder samples prepared with the P3 and P4 solutions have an amorphous structure that is closer to the cristobalite, and therefore is easier to crystallize into that phase. Some authors have also pointed out the resemblance between the structures of hsed silica and the cristobalite [7].…”

“…Si02 bulk samples and coatings containing silver were prepared using the traditional sol-gel method [4,5], with the starting solution composed of tetraethyl-orthosilicate (TEOS), water and ethanol. The ethanol to TEOS molar ratio was 4: 1 in all samples, and four water to TEOS molar ratios were used: 3.33, 5, 7.5 and 11:1, hereafter these values will be referred as P1, P2, P3 and P4, respectively.…”