In this study, we present the effects of the morphological modification of an oxygen-sensing film on improving the sensitivity of luminescent oxygen sensors. Pores were made inside the volume and on the external surface of the oxygen-sensing film consisting of platinum(II) octaethylporphyrin (PtOEP) oxygen-sensitive dye embedded in a polystyrene (PS) polymer matrix. The size of the pores with diameters from 300 nm to 1 μm was controlled through the phase separation of the ternary system of PS, polyethylene glycol (PEG), and chloroform. Photoluminescence (PL) intensity and oxygen accessibility of the oxygen-sensing film were considered the main factors affecting the sensitivity of the sensors. PL intensity was analyzed through the diffused reflectance and absorbance of the oxygen-sensing film. Oxygen accessibility was analyzed based on the Langmuir-Hill absorption theory by considering the sensitivity saturation behaviors of the oxygen-sensing film above the excitation light source intensity of 1000 cd/m2. The optimized porous-structured oxygen-sensing film showed 61% higher sensitivity than the solid oxygen-sensing film. According to the measurement results, the sensitivity enhancement in the porous sensing film was significantly more driven by the increase in oxygen accessible sites than the increase in PL intensity. Furthermore, the sensing film with pores only on its external surface and not inside its volume showed 72% enhanced sensitivity relative to the solid sensing film. Therefore, the external surface area of the sensing film affects the sensitivity of the oxygen-sensing film significantly more than the pores inside the volume of the sensing film because the external surface acts as an oxygen diffusion barrier that limits the amount of oxygen that can access the oxygen-sensitive dye embedded in the polymer matrix.
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© 2017 Elsevier B.V.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Surfaces, Coatings and Films
- Metals and Alloys
- Electrical and Electronic Engineering
- Materials Chemistry