Photoluminescence of Up-Conversion Nanoparticles with High Spatial Resolution

Up-conversion nanoparticles (UCNPs) are highly attractive for avoiding autofluorescence in application cases in biosensing and imaging. Characterizing the photophysical properties of such nanoparticles is essential to enhance the efficiency of preparation methods as well as their electronic and optical properties. Up-conversion is a strongly power dependent energy-transfer process which is based on excitation in the NIR and photon emission in visible range. The commonly used steady-state methods (i.e. excitation and emission spectroscopy) provide valuable insights into the photophysics of samples. However, such results give only a partial view of a sample’s behavior after photoexcitation. A further piece of the puzzle is often revealed by performing time-resolved luminescence spectroscopy. Combination of spectral and lifetime information of a sample’s luminescence allows for a deeper insight into photophysical processes occurring after light absorption. This can be further enhanced by including spatial information. Time-resolved photoluminescence (TRPL) imaging is a powerful technique for characterizing and inferring structural-to-photophysical relationships in up-conversion materials. Additionally, the kind of imaging method and the power applied to the sample are further parameters which are important for<br/>understanding TRPL imaging results. Gathering such information and knowing the chosen parameters are important steps toward the optimization of structure as well as preparation process of UCNPs, resulting in increased performance of such materials.<br/>We will demonstrate here the performance of a spectrometer-microscope assembly for characterization and analysis of UCNPs in terms of lifetime, spectral, and spatial resolution, which provides more information in combination than can be obtained using only lifetime or only steady-state experiments.