Exploration of thin polymer films for phosphor thermometry

The investigation of phosphor-doped polymer films is a promising avenue for thermometry applications. It has been previously demonstrated that phosphor-doped thick polymer films prepared by drop-casting method will luminesce with high brightness and preserve the same temperature-dependence of the emission as the neat phosphor powder. However, there will be some cases for which a thick film will not be suitable. Thermal equilibration with the substrate to which it adheres could be a problem in high heat flux situations, for example when there is a large temperature difference with the surrounding environment. In such instances, heat transfer and conduction issues are of greater importance. This is one impetus for exploring thinner films as thermographic sensors. The effort described here extends the exploration of La2C2S:EU phosphor-doped polymer materials to much thinner films, between 0.1 and 0.4 mm created by means of spin-coating technology. The results described here cover dopant concentration levels ranging from 5 to 50 wt%. For this investigation, either a 365 nm LED or a 405 nm laser diode was used to provide excitation and the 5D2 state near 510 nm was monitored. The excitation/emission behavior was thoroughly characterized from-20 to 75 °C. In spite of the thinness of the films created here, the measured signal intensity for different temperatures is sufficient for a number of applications that the authors envision, from aerospace to biomedical research. Given that the signal levels increase as temperature decreases, lower temperature applications such as cold-chain biologistics are suggested