Compositions based on rare earth sulfides, process of preparing them, colored pigments, use of compositions and colored pigments and matter compositions

摘要

Novel compositions based on coloured rare-earth sulphides of core-shell type, which are characterised in that they include (i) a support based on at least one rare-earth sesquisulphide of formula M2S3 in which M denotes at least one element taken from the group consisting of the lanthanides of atomic number between 57 and 71 inclusive, preferably cerium, and yttrium, the said support additionally containing at least one alkali metal and/or alkaline-earth metal element, preferably sodium, at least a part of which, and preferably all of which, is included in the crystal lattice of the said sesquisulphide, and (ii) a layer based on at least one transparent oxide, preferably silica, deposited at the surface of the said support and coating the latter. The invention also relates to a process for obtaining these compositions, which consists (i) in bringing the support and a precursor of the desired transparent oxide into contact, (ii) in precipitating, according to a number of possible methods (hydrolysis, basic precipitation or other), the transparent oxide and, finally, (iii) in separating the composite obtained from its reaction mixture. Finally, it relates to the use of the said compositions for colouring various materials, in particular plastics.