Holmium(III) sulfide is the sulfide salt of holmium, with the chemical formula of .
Holmium(III) sulfide can be obtained by the reaction of holmium(III) oxide and hydrogen sulfide at 1325 ðC.
It can also be prepared by treating holmium(III) sulfate with hydrogen sulfide at elevated temperatures.
In another preparation, it can be produced by treating metallic holmium with sulfur:
Once prepared, holmium(III) sulfide can be purified by chemical vapor transport using iodine.
Holmium(III) sulfide has orange-yellow crystals in the monoclinic crystal system, with the space group P2<sub>1</sub>/m (No. 11). Under high pressure, holmium(III) sulfide can form in the cubic and orthorhombic crystal systems.