Optical investigation of the quasi two-dimensional monophosphate tungsten bronzes KxP4W8O32 (x = 0 - 1.57)S. Haffner, M. Dressel, D. Groult and C. SchlenkerEur. Phys. J. B, 24 2 (2001) 167-175DOI: https://doi.org/10.1007/s100510170004