Impact of proton irradiation on photoluminescent properties of C-doped ZrO2 films prepared by ALD

Amorphous C-doped zirconia thin films grown by ALD technique on fused silica substrates have high transmittance and significant photoluminescence (PL) capacity suitable for application as a transparent material to convert high energy into lower energy photons as well as an optical sensor of radiation. Due to carbon doping, zirconia films present three main PL transitions: Transition I and II at λem = 450 nm (λexc = 200 and 270 nm), related to sp3 and sp2 C–C bonds, and Transition III at λem = 450 nm (λexc = 300 nm) that can be assigned to C[dbnd]O bonds which introduce n levels in the π- π* gap. Protons with energy of 100 keV and two values of fluence (1∙1012 p+/cm2 and 5∙1014 p+/cm2) were used to modify the film properties. The changes induced by the radiation in the chemical composition of the films have been monitored as a function of irradiation dose using in-depth resolved XPS analysis which evidenced modification of C–Zr, Zr–O, C–H, C–C/C[dbnd]C and C[dbnd]O bonds. We demonstrate that C–Zr bonds formed in the film depth are cleaved by protonation in favor of Zr–O, C–H and C[dbnd]O bonds establishment. As a consequence, more defect levels are formed in the π- π* gap of carbon. Consequently, the emission due to Transitions III becomes more intense for high energy doses, getting intensity values close to Transitions I/II.