Probing zinc oxide as a semiconductor photosensitizer of energetic materials to laser radiation

The development of methods for laser ignition of energetic materials opens up significant prospects for improving the safety of their application. The photochemical processes can increase the selective sensitivity of energetic material to laser radiation and make the most of its capabilities. The paper considers the application of zinc oxide as a photosensitizing additive capable of significantly reducing the laser ignition threshold of pen-taerythritol tetranitrate (PETN). The dependencies of the laser initiation threshold by the fundamental frequency (1064 nm), second (532 nm), and third harmonic (355 nm) of an Nd:YAG laser on the concentration of zinc oxide were studied. The ignition threshold energy density is reduced by a factor from 2 to 5, depending on the oxide concentration and the laser radiation wavelength. The proposed initiation mechanisms based on the results of the several spectroscopy methods were discussed for each laser harmonic. Laser ignition of the PETN-ZnO composite through the ultraviolet laser radiation combined the thermal and photochemical mechanism. Visible laser har-monic (532 nm) drives a purely photochemical initiation of the PETN. The obtained results indicate that a mechanism of initiation by visible light should be caused by the charge transfer in the ZnO-PETN interface. The reported experimental result does not only serve as an example of the successful photochemical ignition of energetic material but also shows that processes, techniques, and materials of semiconductor photocatalysis are applicable to laser initiation.