Se has been sorbed into the pore system of Cu2+-ion exchanged Y zeolite to investigate the effect of transition metal countercations on the structure and electronic properties of the incorporated semiconductor. Results from anomalous x-ray scattering experiments at the Se K-absorption edge and Raman measurements show the formation of isolated, strongly disordered Se-x chains (x --> infinity) with an intrachain bond length of 2.39 Angstrom. The difference pair correlation function T-Se(r) exhibits a short-range pair correlation at 3.30 Angstrom, which is attributed to specific Cu2+-Se-x interactions. The optical spectrum of the composite is characterized by a strong absorption band around 400 nm with a shoulder at 450 nm and an optical band gap of 2.09 eV. The strong Cu2+-Se-x correlation is explained by charge transfer from the Se-x chains to the cations, and the formation of band gap states is postulated to account for the unusually long intrachain bond length and the remarkably small band gap.