Near-infrared and upconversion emission of Tm3+ and Tm3+-Yb3+ codoped transparent oxyfluoride glass-ceramics

In the present study, oxyfluoride glass-ceramics (GCs) with crystalline phase NaLaF
4
doped with TmF
3
and codoped with YbF
3
have been prepared by Spark Plasma Sintering (SPS), and their optical properties characterized and compared with GCs prepared by the conventional thermal treatment method. The spectroscopic properties of the near infrared and upconverted emissions of $\mathrm{Tm}^{3+}$ ions have been characterized by using steady-state laser spectroscopy. The energy transfer between $\mathrm{Yb}^{3+}$ and $\mathrm{Tm}^{3+}$ ions is confirmed by the near-infrared (NIR) and upconversion emissions after $\mathrm{Yb}^{3+}$ excitation at 975 nm. Back transfer from $\mathrm{Tm}^{3+}$ to $\mathrm{Yb}^{3+}$ is also present under near-infrared excitation of $\mathrm{Tm}^{3+}$ ions at 791 nm. Blue, red, and NIR upconverted emissions are only observed in $\mathrm{Tm}^{3+}-\mathrm{Yb}^{3+}$ codoped samples after 975 nm excitation, thus confirming the effective energy transfer between $\mathrm{Yb}^{3+}$ and $\mathrm{Tm}^{3+}$ ions.