The absolute photoyields of chemical vapor deposited (CVD) diamond and amorphous hydrogen-free diamondlike carbon (DLC) films, in the range of 140–300 nm, are reported. CVD diamond films exhibit a large photoyield, of a few percent in the range 140–180 nm. DLC films have a 20–50 times lower yield. Post growth hydrogenation is found to substantially increase the photoyield of CVD diamond films. We discuss the applicability of these films as UV photocathodes coupled to electron multipliers based on gaseous charge multiplication. ©1997 American Institute of Physics.