We investigated a-C:H films deposited by dual electron cyclotron resonance radio frequency plasma-enhanced chemical vapour deposition (PECVD) by optical absorption and electron spin resonance (ESR) spectroscopy. We show that the variation of the density of paramagnetic centers obtained from ESR spectroscopy can be directly correlated to the low energy part of the optical absorption spectrum revealed by photothermal deflection spectroscopy (PDS). A simple analysis of the low energy part of the optical absorption spectrum is proposed, which allows an assessment of the density of states at the Fermi level. We interpret this result in terms of intraband transitions of localized defects situated far from the pi-pi* band tails, which dominate the higher energy part of the optical absorption spectrum. (c) 2004 Elsevier B.V. All Rights Reserved.