Photoluminescent properties of MCM-41 molecular sieves

The photoluminescence of as-synthesized and calcined siliceous as well as aluminosilicate MCM-41 molecular sieves was examined at 350, 300, 250 and 200 nm. The observation of high energy emission bands (hv>2.5 eV) from the as-synthesized siliceous MCM-41 suggests the presence of oxygen related defect sites similar to those found in amorphous silica. Examination of corresponding excitation spectra does not rule out this possibility. Upon calcination, the intensity of the photoluminescent signal decreases dramatically. Little decrease in photoluminescence intensity is observed for the calcined aluminosilicate MCM-41 molecular sieve. The intensity of the emission of the aluminosilicate MCM-41 appears to be correlated to the presence of framework aluminum (i.e. large amounts of aluminum incorporated into the framework generate a large photoluminescence signal). (C) 1998 Elsevier Science B.V.