Organic–inorganic hybrid glasses of selective optical transmission

Organic–inorganic hybrid glasses were obtained by the sol–gel method using as starting materials tetraethoxysilane (TEOS) and the gel modifier, diethoxydimethylsilane (DEDMS). The effect of various molar ratios of DEDMS and TEOS on the quality of gels has been determined. It has been found that transparent gels can be obtained only at the molar ratio DEDMS:TEOS ⩽1. To determine the effect of DEDMS addition on the structure and microstructure of silica gel derived from TEOS, FTIR spectra of gels were measured and the porous structure was examined. From FTIR data it follows that DEDMS accelerates polycondensation reaction already at 40°C; the evidence of it is the loss of the band at 950 cm−1 characteristic for Si–OH groups in the spectra of gels modified by DEDMS. The examinations of porous structure of gels showed that DEDMS causes some reduction of the specific surface area of gels and small increase of the dimensions of pores. The organic dye (2′,7′ dichlorofluorescein) was introduced into both, silica gel and organically modified (DEDMS) silica gel. The optical absorption in the ultra-violet and visible wavelengths of hybrid glasses as well as the thermal stability of colour up to 200°C were determined. The colour derived from the 2′,7′ dichlorofluorescein depended in the first place on the thermal treatment parameters and was stable to 100°C; heating of gels to 200°C reduced the colour intensity. Any effect of DEDMS addition on the optical absorption of gels containing organic dye was not observed.