We report of parameters by which one can construct dielectric functions of Cd-1-xMgxTe alloy films for any composition x (0less than or equal to x less than or equal to0.43) in the energy range 1.5-6.0 eV using the parametric semiconductor model. The parametric model describes analytically the dielectric functions of semiconductor materials as a sum of Gaussian-broadened polynomials and provides a reasonably accurate representation. The dielectric function spectra we used as a basis were obtained on films with Mg compositions x = 0.00, 0.23, 0.31 and 0.43, with overlayer effects minimized by chemical etching. The appearance of well-defined interference-oscillation patterns below the E-0 bandgap and the excellent separation of the E-2 peaks confirm that the dielectric functions constructed in this work represent the best room-temperature optical responses of Cd-1-xMgxTe alloys (0.00 less than or equal to x = 0.4) from 1.5 to 6.0 eV to date. (C) 2004 Elsevier B.V. All rights reserved.