In-Band Luminescence Thermometry in the Third Biological Window and Multicolor Emission of Er-Doped Fluoride and Oxide Nanoparticles

In this study we present a morphological and spectroscopical characterization of three different erbium doped nanocrystal samples, namely two oxides (Y2O3:3%Er, Sc2O3:3%Er) and one fluoride (YF3:5%Er). The spectroscopic study offers a comprehensive comparison of their multicolor emissions, ranging from the visible to the mid-infrared region. Emissions from the first five excited states are presented and the emission cross sections of the 4I11/2 → 4I15/2, 4I11/2 → 4I13/2, and 4I13/2 → 4I15/2 transitions have been calculated and compared with literature results for the oxide compounds providing a confirmation for the 1.5 μm emission of Er:Y2O3, a correction over published values for the 2.7 μm emission of Er:Y2O3, and also new results for the Er:Sc2O3 emission cross section values of all the infrared bands. Moreover, this study explores the application of the 4I13/2 emission for in-band luminescence thermometry within the third biological window. An optimized segmentation of the 1.5 μm emission permits to achieve high relative and absolute sensitivities using just one dopant ion.