Enhanced photoluminescence of oxygen sensing films through doping with high dielectric constant particles

A uniquely simple approach to increase the intensity of the photoluminescence (PL) of dye-doped sensor films is demonstrated for oxygen sensors, where the sensor film, i.e., Pt or Pd octaethylporphyrin (PtOEP or PdOEP, respectively)-doped polystyrene, is additionally doped with small-size particles that have a high dielectric constant, such as 360 nm-diameter titania (TiO2) particles. When excited by an organic light emitting device (OLED), the dye PL intensity increases up to similar to 10 fold, depending on the TiO2 concentration and the excitation source. The enhanced PL is attributed to light scattering by the embedded particles and possibly by voids in the film. The particles scatter the light that excites the PL, increasing the optical path of the exciting light and consequently the absorption of that light and the PL. The particles can also result in an increase in the PL outcoupling, reducing waveguiding to the film edges. The increased PL results in an improved signal-to-noise (S/N) ratio in oxygen monitoring, without any deterioration or change in the response time or the long-term stability of the sensor films. In addition, at a given O-2 level, the dye PL decay time tau increases in the presence of the particles, but is independent of their concentration in the measured range. The improved S/N can improve the analyte limit of detection, allow shortened data acquisition times, and enable the use of low-intensity excitation sources to minimize potential dye photobleaching. In particular, it improves the performance of structurally integrated OLED-based chemical and biological sensors, which are drawing increasing attention due to their uniquely simple and flexible integration geometry.