Effects of pressure on the optical absorption and photoluminescence of Wöhler siloxene

We have investigated the effect of hydrostatic pressure (P5 GPa) on optical absorption and photoluminescence spectra of Wöhler siloxene (Si6O3H6, as prepared) at T=300 K. The absorption edge energy near 2.75 eV decreases linearly with pressure at a rate of -30 3 meV/GPa. For the position of the maximum of the green luminescence band we find a similar pressure coefficient (dE/dP=-24 3 meV/GPa). The intensity of the green luminescence shows a reversible decrease with increasing pressure. The pressure dependence of interlayer and intralayer lattice constants has been determined by x-ray powder diffraction. The observed changes in optical transition energies are discussed in the framework of a semiempirical quantum-chemical calculation of the electronic structure of siloxene.