Luminescent oxygen-sensing films with improved sensitivity based on light scattering by TiO2 particles

Abstract

We investigated the effects of embedded titanium dioxide (TiO2) nanoparticles on the photocurrent and sensitivity of luminescent oxygen-sensing films based on platinum octaethylporphyrin (PtOEP), which is an indicator dye. The TiO2 nanoparticles acted as light-scattering centers in the sensing films, and the light-scattering performance was evaluated in relation to TiO2 nanoparticle diameter and crystal structure. In the presence of embedded light-scattering particles, the probabilities of PtOEP molecules encountering and being excited by light were expected to increase, resulting in improvement of the photoluminescence and sensitivity of the sensing films to oxygen gas. The diameter of the TiO2 nanoparticles was changed by laser irradiation while they were dispersed in acetone. Through the laser irradiation, the particle size of the TiO2 nanoparticles grew, and their morphology became spherical. The X-ray diffraction (XRD) analysis showed that the crystalline structure of the TiO2 nanoparticles changed in relation to its calcination temperature. The photocurrent and sensitivity of the sensing films with embedded TiO2 nanoparticles in relation to the oxygen gas concentration were measured using a green light-emitting diode (LED) as the light source and an Si photodiode as the photocurrent measuring device. Based on the results, it was confirmed that the photocurrent and sensitivity of the oxygen-sensing films were greatly improved with increases in the size and refractive index (n) of the embedded TiO2 nanoparticles. Furthermore, the improvements in the photocurrent and sensitivity of the oxygen-sensing films allowed the fabrication of a high-resolution oxygen-sensing film that can detect the oxygen distribution over large areas.