CuGaSe2 thin films have been prepared by rapid thermal processing of stacked elemental layers on different substrates. The film homogeneity across the depth and the influence of the substrate used have been investigated mainly by means of photoluminescence spectroscopy. The photoluminescence spectra could be divided into five spectral ranges: emissions from Ga-rich phases (above 1.75 eV), band edge emissions (1.72 eV), emissions involving shallow levels (V-Cu, V-Se), a broad donor-acceptor-pair transition (1.4-1.55 eV), and emissions from deep levels (below 1.4 eV). All films grown from the conventional precursor stack showed inhomogeneities, which could be avoided by modifications of the precursor stack. Investigations on the growth on different substrates revealed the best crystalline properties for films grown on sapphire. In contrast to films grown on floating glass the difference in quality to CuGaSe2 on Mo was rather small. This underlines the suitability of Mo-coated floating glass as cheap substrates for thin-film solar cells.