Thallium ( I ) bromide turns yellow when exposed to light , similar to silver ( I ) bromide . Thallium ( I ) sulfide is black , similar to silver ( I ) sulfide . Thallium ( I ) bromide is a photosensitive yellow compound very similar to the silver bromide , while the black thallium ( I ) oxide and thallium ( I ) sulfide are very similar to the silver oxide and silver sulfide .