Thulium(III) oxide is a pale green crystalline compound, with the formula Tm2O3. It was first isolated in 1879, from an impure sample of erbia, by Swedish chemist Per Teodor Cleve, who named it thulia.

Synthesis

Thulium(III) oxide has been made in the laboratory using various methods. One method involves burning thulium metal or its various salts in air. Thulium(III) oxide can be made using a hydrothermal method where thulium(III) acetate is mixed with an ammonia solution, which causes thulium(III) oxide to precipitate as a white solid.

Properties

Thulium(III) oxide (Tm₂O₃) is a pale green, thermally stable powder with a high melting point of 2,341 °C and a density of 8.6 g/cm³, typically forming a cubic crystal structure. It is resistant to oxidation and dissolves in strong acids like hydrochloric acid, allowing it to form soluble thulium salts. Due to its unique f-electron configuration, Tm₂O₃ has notable optical properties. Thulium oxide (Tm₂O₃) is considered fibrogenic; it has the potential to induce tissue injury and fibrosis when inhaled or otherwise introduced to biological tissue.