Element category: lanthanide
Thulium is a bright, lustrous, soft, malleable, silvery rare earth metal, a member of the lanthanide group of the periodic table. It is the second least abundant of the lanthanides only after promethium.
Thulium metal is rare and expensive, so it almost has no commercial applications. Holmium-chromium-thulium triple-doped Yttrium aluminum garnet (Ho:Cr:Tm:YAG, or Ho,Cr,Tm:YAG) is an active laser medium material with high efficiency. Thulium isotopes can be used as a X-ray source.