Up-converting thermographic phosphors are of interest due to specific advantages for temperature measurement applications. Typically, infrared excitation stimulates visible fluorescence only from the target phosphor and not the surrounding medium. This is in contrast to ultraviolet excitation which may also produce interfering luminescence from cells and other biological tissue in the vicinity, for instance. When traversing a material, usually infrared losses due to scattering and absorption are less than for ultraviolet wavelengths. An example is human skin.
This investigation follows logically from earlier efforts incorporating thermographic phosphors into thin samples of PDMS and Aerogels. Thin samples of phosphor-doped PDMS are compliant and their function as a reusable temperature sensor has been previously demonstrated by the authors. Layered phosphor/PDMS/Aerogel composites are being investigated for heat flux sensing. For maximum utility and understanding; physical, optical, and thermal properties are characterized over a wide temperature range.
Lanthanide-doped up-converting phosphor composites with increasing concentrations were synthesized for this study and fully characterized as a function of temperature. The excitation/ emission characteristics of the powder alone and the prepared composite thin films were investigated between -80 C and +80 C in an environmental chamber and the decay behavior of each sample type was measured. Thin film composites were prepared using spin-coating techniques and the excitation/ emission behavior was characterized as a function of film thickness also. Here, the authors report on decay behavior and spectra as a function of temperature and emission intensity of the composite films as a function of excitation wavelength. Results were compared with powder –only parameters and are reported here.