The sol-gel process

which is mainly based on an inorganic polymerization reaction

is a chemical synthesis method initially used for the preparation of inorganic materials such as glasses and ceramics.The mild characteristics offered by the sol-gel process allow the introduction of organic molecules inside an inorganic network.Inorganic and organic components can then be mixed at the nanometric scale

in virtually any ratio leading to so called hybrid organic inorganic nanocomposites.These hybrids are extremely versatile in their composition

processing and the related optical and mechanical properties.Sol-gel derived silica gel(aerosol or serogel) is of great importance based on its wide applications in optics

catalysts

sensors and solar energy collectors.Organic dyes and rare earth ions have been incorporated into the microporous silica gel

which is generally considered to possess an optically inert framework.However

the sol-gel derived silica gel is not optically inert

but optically active

i.e.

it shows lminescence usder UV excitation.Of particular interest and importance is that

a new class of stable and efficient white photoluminescent silicate materials has been obtained from an alkoxysilane and a carboxylic acid through sol-gel route.Other related report is the sol-gel derived undoped usea cross linked organic inorgels which display strong blue light emission.In this paper

undoped SiO

2

xerogels were prepared by the sol-gel method under various preparation conditions and compositions by using tetracthoxysilane(TEOS)and (3-aminopropyl) triethoxysilane(APS)

orgaic acid (CH

3

COOH)and in orgagic acids (HCl

HNO

3

H

2

SO

4

) as the main precursor.Luminescence spectra were used to characterize the resulted SiO

2

xerogels.Under the excitation of 365nm all the xerogels exhibit strong luminescence in the blue region

but the emission intensity and position depend on the starting precureor compositions to a large extent.Suitable amount of polyethylene glycol(PEG500 and PEG10000)in the SiO

2

xerogels can enhance the emssion intensity.Additionally

the emission intensity of the hybrid xerogels in creases with heat treatment temperature in the range of ambient to 200℃

and vacuum condition is also able to enhance the emission intensity.