Chemistry Reference
In-Depth Information
TABLE 8.3
Matrix of Rare Gas (Rg
2
), Halogen (X
2
), and Rare Gas Halide (RgX
∗
) Excimers
and Their Emission Maxima
Rare Gas (Rg)
He
Ne
Ar
Kr
Xe
Halogen (X
2
)
74nm
83nm
126nm
146nm
172nm
F
157nm
108nm
193nm
248nm
354nm
Cl
259nm
175nm
222nm
308nm
Br
289nm
165nm
207nm
282nm
I
342nm
190nm
253nm
trappingdonottakeplaceandexcimershavealsobecomeattractiveasincoherentlight
sources [60,65,66]. Modern excimer lamps are based on the efficient fluorescence of
UV and VUV radiation of excimers, which is converted into visible light by means
of appropriate phosphors. DBDs, capacitive discharges, and microwave excitation
have been used to drive excimer lamps. Industrial applications of excimer lamps
are cleaning of substrates, water and air purification, UV curing and modification
of polymer surfaces, low-temperature oxidation of semiconductors, and UV-induced
deposition of different materials [67,68]. In addition, flat-panel plasma TV sets are
a modern excimer application. A plasma display panel (PDP) is essentially a matrix
array of very small discharge cells, where the plasma in each cell is generated by
DBD [69].
In the following, the main plasma-chemical processes required to form excimers
in rare gases and rare gas halide mixtures are discussed.
8.1.3.1 Main Processes of Excimer Formation in Rare Gases
The efficient excimer formation requires electrons (e
−
) with an energy of at least 10
to 25 eV. These electrons are able to generate excited atoms (Rg
∗
)orions(Rg
+
)of
the rare gas in direct collisions of electrons with rare gas atoms (Rg) in their ground
state according to
e
−
→
Rg
∗
e
−
,
Rg
+
+
(8.13)
+
e
−
→
Rg
+
+
2e
−
.
Rg
(8.14)
In excimer light sources, the generation of rare gas ions is usually dominated
by stepwise excitation of excited rare gas atoms (Rg
∗
) to the higher excited atoms
(Rg
∗∗
)via
Rg
∗
e
−
→
Rg
∗∗
e
−
+
+
(8.15)
followed by the stepwise ionization mainly according to
Rg
∗∗
+
Rg
+
+
e
−
→
2e
−
.
(8.16)
