gamma-CuCl semiconductor material has been identified as a candidate material for the fabrication of blue-UV optoelectronic devices on Si substrates due to its outstanding electronic, lattice and optical properties. However, CuCl thin films oxidise completely into oxyhalides of Cu II within a few days of exposure to air. Conventional encapsulation of thin gamma-CuCl by sealed glass at a deposition/curing temperature greater than 250 degrees C cannot be used because CuCl interacts chemically with Si substrates when heated above that temperature. In this study we have investigated the behaviour of three candidate dielectric materials for use as protective layers for the heteroepitaxial growth of gamma-CuCl on Si substrates: SiO2 deposited by plasma-enhanced chemical vapour deposition (PECVD), organic polysilsesquioxane-based spin on glass material (PSSQ) and cyclo olefin copolymer (COC) thermoplastic-based material. The optical properties (UV/Vis and IR) of the capped luminescent CuCl films were studied as a function of time, up to 28 days and compared with bare uncapped films. The results clearly show the efficiency of the protective layers. Both COC and the PSSQ layer prevented CuCl film from oxidising while Si02 delayed the effect of oxidation. The dielectric constant of the three protective layers was evaluated at 1 MHz to be 2.3, 3.6 and 6.9 for COC, Si02 and PSSQ, respectively. (c) 2005 Elsevier B.V. All rights reserved.