  We report the complete characterization of various cooling grade Tm-doped
crystals including the first demonstration of optical refrigeration in Tm:YLF
crystals. Room temperature laser cooling efficiencies of 1% and 2% (mol)
Tm:YLF, and 1% Tm:BYF crystals at different excitation polarizations are
measured and their external quantum efficiency and background absorption are
extracted. By performing detailed low-temperature spectroscopic analysis of the
samples, global minimum achievable temperatures of 160 K to 110 K are
estimated. The potential of Tm-doped crystals to realize mid-IR optical
cryocoolers and radiation balanced lasers (RBLs) in the eye-safe region of the
spectrum is discussed, and a promising 2-tone RBL in a tandem structure of
Tm:YLF and Ho:YLF crystals is proposed.
