Candoluminescence of rare earths

The emission spectra of sesquioxides, as well as mixed oxides of thorium(IV) or yttrium(III), containing various Lanthanides, were studied in the form of Auer mantles heated in blue flames of natural gas or hydrogen. Like Ce(IV), praseodymium and terbium (even as traces) produce broad, continous spectra, whereas trivalent neodymium, holmium, erbium and thulium provide narrow bands at slightly Lower wave-numbers than absorption bands of aqua ions. The emission seems determined by Kirchhoff's theorem without significant contribution from chimoluminescence.