Photoluminescence and bonding structure evolution of amorphous carbon films with laser intensity

The hydrogen-free diamond-like carbon (DLC) films were prepared at different laser intensities by pulsed laser ablating a graphite target in vacuum circumstance at room temperature. By varying the laser intensities from 2.5×108 to 7.5×108 W/cm2 the room-temperature photoluminescence (PL) was found in the range of 580–800 nm. The PL integrated intensity was decreased with increase of laser intensity up to 5.0×108 W/cm2 and then was increased thereafter. Over the same laser intensity region a similar variation trend of the deposition rates of films can be observed. The bonding structure of the carbon atoms in the films was characterized by Raman spectroscopy. Raman measurement showed that the sp2 bonded fraction increased at low or high laser intensity, while reached a minimum value at 5.0×108 W/cm2. The results indicate that laser intensity has a strong influence on the PL properties of the DLC films and the evolution of the PL was deduced to be correlated with the changes of sp2 fraction.