Tunable upconverted visible light and high sensitivity optical thermal sensing of Ln, Yb:Y6O5F8 nanotubes

Micron-sized bundles of highly crystalline individual nanotubes of Pbcm Vernier-type Yb3+-sensitized Ln3+ (Er, Pr)-doped Y6O5F8 oxyfluorides have been prepared through efficient low-temperature hydrothermal syntheses. Under near infrared (NIR) 978 nm diode laser excitation, the color of the upconverted light from codoped Pr, Er, Yb:Y6O5F8 nanotubes can be selected by the control of the Pr3+ concentration, and by the excitation regime and power density. Samples with low Pr3+ concentration emit predominantly green light, and the selection between bluish-green light and white light has been demonstrated with large Pr3+ concentration (2 mol%), under pulsed or continuous wave excitation, respectively. Involved Er3+ and Pr3+ electronic transitions and mechanisms to populate their corresponding emitting levels have been analyzed for a large number of 2 mol% Yb3+-sensitized, 0.05 mol% Er3+-doped oxyfluoride samples within the Pr3+ concentration span 0.2 - 2 mol% [1]. Furthermore, the ratiometric analysis of the thermal evolution of intensities of NIR excited green upconverted emissions from thermally coupled 2H11/2 and 4S3/2 Er3+ multiplets of Er, Yb:Y6O5F8 indicates thermal sensing potential with better sensitivity S (0.0041 KK-1) than hexagonal Er, Yb:beta-NaYF4(0.0032 K-1) in the temperature range of physiological interest.