When conductor or semiconductor materials are
exposed to microwave radiation in different atmospheres (Ar, He,
N2, and O2+N2) intense discharge phenomena are observed. The
discharge phenomena, generated when strips of the metals Fe, Al,
and Zn or particles of the semiconductor SiC are irradiated with
microwaves, are characterized experimentally using spectrum
acquisition and analysis. Filamentary discharge is observed in
an Ar atmosphere while spark discharge is observed in He, N2,
and O2+N2 atmospheres. The spectral lines of the discharges
are concentrated mainly in the visible region, but there are also
peaks in the ultraviolet region. The nature of the discharge and
the specific details of the spectra are influenced by: 1) the target
metal or semiconductor used; 2) the atmosphere; and 3) the
microwave field characteristics. The spectra always consist of two
parts: one corresponding to the target metal or semiconductor
irradiated by the microwaves and the other due to the formation
of the high-energy excitation states of atoms, molecules, and
ions induced in the gaseous atmosphere. The microwave-induced
discharge and the corresponding luminous and plasma effects
have potential uses as energy sources in many applications
including chemical or photocatalytic enhancement of reactions
and the destruction of volatile organic compounds for which
preliminary results are encouraging.