Lifetime-based luminescence thermometry from Yb3+/Er3+codoped nanoparticles suspended in water

The thermal sensing capabilities of Y2O3:Yb3+/Er3+ codoped nanoparticles (NPs) have been extensively studied in recent years for remote luminescent thermometry. However, the use of intensity-based methods for temperature sensing in biological media may be hindered by tissue-induced spectral artifacts, such as light scattering and absorption. To explore alternatives to intensity-based techniques towards bio-sensing applications, we present lifetime-based nanothermometry experiments conducted with a suspension of Y2O3:Yb3+/Er3+ NPs in water. Time-resolved measurements were performed regarding the luminescence from the 2H11/2 (525 nm), 4S3/2 (545 nm), and 4F9/2 (660 nm) excited states of Er3+ for temperatures ranging from 298 K to 338 K. A simplified effective-phonon model was proposed to explain the measured decrease in lifetimes with increasing temperature. The thermometers presented relative sensitivities S ������ of 0.31% K-1, 0.34% K-1 at 310 K for the luminescence bands centered at 525 nm, 545 nm, respectively, and a best ������������ value of 0.50% K-1 at 310 K for luminescence at 660 nm. The results obtained with the red-emitting band under green excitation demonstrate that the lifetime-based nanothermometers can present high S ������ if compared to intensity-based sensors, reinforcing their potential for applications in aqueous and/or biological media.