| abstract |
A near-infrared absorbing filter which does not contain antimony, arsenic or the like and is excellent in heat resistance is disclosed. The near-infrared absorbing filter is characterized by containing a compound composed of a salt of cations obtained by oxidizing a substance represented by the formula (1) below and anions (X), which are alkylsulfonic acid ions having 1-8 carbon atoms that are necessary for neutralizing the cations and not substituted or may be substituted with a halogen atom, a lower alkoxy group, a cyano group, or a hydroxyl group. (1) (in the formula (1), rings A and B may have a substituent, and R1-R8 independently represent a substituted or non-substituted alkyl group, cycloalkyl group, alkenyl group or aryl group having 1-8 carbon atoms.) |