[0001] The present invention relates to a VUV excimer lamp according to the preamble of
claim 1 and to an excimer lamp system and a photochemical unit comprising such a VUV
excimer lamp.
[0002] Excimer lamps are used for generating high-energy ultraviolet (VUV) radiation. The
excimer emission is generated by means of silent electrical discharge in a discharge
chamber filled with an excimer-forming gas. The discharge chamber has walls formed
from a material transparent to ultraviolet (UV) light. A first electrode is disposed
within the chamber. A second electrode is arranged outside of the chamber. Due to
the electric field generated between the electrodes a discharge occurs, generating
excimer molecules. When these excited molecules return to ground state, high-energy
ultraviolet light is emitted.
[0003] It is known to use a phosphor layer on the inner surface of the discharge chamber
for ultraviolet light generation.
CN 103972040 discloses an excimer lamp for sterilization in a refrigerator. A phosphor layer converts
the wavelength of light emitted by the discharge medium into a longer wavelength.
By altering the materials of the phosphor layer, light with various wavelengths can
be obtained. The phosphor layer being located on the inside of the discharge chamber
is subject to the discharge plasma which has a negative effect on the lamps lifetime.
Multiple phosphor layers for light conversion are known from prior art, e.g.
US 6,734,631 B2 and
US 2005/0073239 A1.
[0004] It is an objective of the present invention to provide an efficient VUV excimer lamp
with an extended lifespan.
[0005] This problem is solved by a VUV excimer lamp with the features listed in claim 1
and by an excimer lamp system and a photochemical unit comprising such a VUV excimer
lamp.
[0006] Accordingly, a VUV excimer lamp comprising a dielectric tube for holding an excimer-forming
gas, a first central electrode disposed within said tube and a second electrode arranged
outside of said tube, is provided, said dielectric tube having a UV fluorescent coating
on the outside. The advantage of such an external coating is that the coating has
no contact with the plasma and can't be destroyed by the discharge.
[0007] In the following Vacuum Ultra-Violet (VUV) radiation is used to describe the UV spectrum
below 190 nm. Ultraviolet C (UV-C) is generally referred to a short wavelength (100-280
nm) radiation, which is primarily used for disinfection, inactivating microorganisms
by destroying nucleic acids and disrupting their DNA, leaving them unable to perform
vital cellular functions.
[0008] Preferably, said dielectric tube is made of quartz glass, which is transparent to
VUV radiation. It is even more preferred that said dielectric tube is made of synthetic
quartz glass, in particular without metal doping.
[0009] It is advantageous, if the UV fluorescent coating is arranged between the dielectric
and the second electrode.
[0010] Preferably, said gas consists essentially of Xe.
[0011] In order to reach high efficiency, said gas should contain less than about 10 ppm
of impurities.
[0012] Preferably, the UV fluorescent coating has phosphorus compounds.
[0013] In a preferred embodiment said UV fluorescent coating is a UV-C fluorescent coating.
[0014] Further, a photochemical unit with a previously described lamp is provided. Photochemical
units can be for example UV disinfection units, UV bleaching units, UV curing units,
UV enhanced chemical vapor deposition units and the like.
[0015] A preferred embodiment of the present invention will be described with reference
to the drawings. In all figures the same reference signs denote the same components
or functionally similar components.
Figure 1 is a schematic side view of a VUV excimer lamp with a phosphor coating arranged
on the outside of the dielectric according to the present invention, and
Figure 2 is a cross section of a principle arrangement of the excimer lamp shown in
figure 1.
[0016] Figure 1 shows a side view of an excimer lamp 1 with a first high voltage central
electrode (inner electrode) 2 arranged in a discharge chamber formed by a dielectric
tube 3. Said first electrode 2 includes an elongated thin wire with an outer diameter
of less than 0.5 mm. It was found that the efficiency of the lamp improved with a
thin wire electrode. In addition, the thin wire electrode 2 shields and absorbs the
VUV radiation to a much lower proportion than conventional wider electrodes, which
leads to efficiency improvement. Preferably, said elongated thin wire is substantially
straight and defines a straight axis of elongation. In other words, the tube has an
elongated wall with cylindrical shape and it extends linearly along the axial direction
of the lamp body. The wire has preferably a circular cross section.
[0017] It is even more preferred that said elongated thin wire has an outer diameter between
0.02 mm and 0.4 mm. Preferably, the inner electrode has a thickness according to the
following equation: (R/ro)/ln(R/ro)> 10, wherein 2*R is the inner diameter of the
dielectric tube 3 and 2*ro the outer diameter of the inner electrode 2. Said elongated
thin wire inner electrode 2 is tensioned and centered with a spring arranged on one
side of the elongated thin wire. This allows to avoid shadow over the length of the
lamp compared to an inner electrode helically wound over the full length around a
rod and to ensure tensioning of the electrode at high temperature, which allows to
keep the coaxial symmetry. The inner electrode 2 is physically connected to each end
of the dielectric tube. The dielectric tube 3 is made of a dielectric, which is transparent
for UV radiation. The space within the dielectric tube 3, between the high voltage
electrode 2 and the dielectric 3 is filled with high purity Xenon gas 5. The water
content is smaller than 10 ppm for performance reasons. A second electrode (outer
electrode) 4 surrounds the dielectric tube 3. This ground electrode 4 can be formed
in different ways. The second electrode 4 is made of a conductive material. For instance,
to form the second electrode 4, a tape or a conductive wire made of a metal (e.g.,
aluminum, copper) may be used. The second electrode 4 is in contact with the outer
surface of the dielectric tube 3. The second electrode 4 can include linear electrodes
40,41. The linear electrodes 40,41 are arranged substantially in parallel with each
other and they extend along the longitudinal axis of the dielectric tube. In another
embodiment the electrodes 4 can be formed in a spiral form on the outer surface of
the dielectric tube 3. This configuration allows discharge to be generated uniformly
in a circumferential direction of the dielectric tube 3, making it possible to obtain
emission with more uniform distribution of brightness. Further, it is possible that
the ground electrode 4 is a mesh or formed by water, which can act with minimal conductivity
as electrode with a vessel being grounded. The first and second electrodes 2 and 4
are connected to a driving circuit (not shown).
[0018] The VUV excimer lamp 1 is used for generation of UV-C radiation for disinfection
purpose. Upon application of a voltage across the first and second electrodes 2 and
4 by a driving circuit, glow discharge occurs inside the dielectric tube 3, which
excites the discharge medium xenon 5. When the excited discharge medium 5 makes a
transition to a ground state, the discharge medium emits ultraviolet light with a
wavelength of 172 nm. The dielectric 3 is coated on the outer surface, with a UV-C
fluorescent material 6, e.g. a layer of phosphorus compounds like YP04: Bi. For a
schematic cross-section of the VUV excimer lamp see figure 2. The ultraviolet light
passes the dielectric tube 3 and excites a phosphor of the phosphor layer 6. The excited
phosphor reemits light in the UV-C range (Stokes shift). The wavelength of the emitted
radiation depends on the composition of the phosphorus layer. It can be adapted to
the application.
[0019] The advantage of such an external coating is that the phosphor layer 6 has no contact
with the plasma and can't be destroyed by the discharge. However, a special dielectric
sleeve 3 is necessary which is able to resist as well as transmit the VUV radiation
to the phosphor. Applicable is for example synthetic quartz, e.g. Suprasil 310, product
and trademark of Heraeus Quarzglas GmbH & Co. KG. It is preferred to use a synthetic
quartz which has no metal doping.
[0020] With the proposed phosphor coating on the outside of the dielectric an efficient
mercury-free UV-C lamp can be provided, which has no warm-up time,□is fully dimmable
(0 to 100% without loss in efficiency) whileDtolerating a wide range of operational
temperature.
1. VUV excimer lamp (1) comprising a dielectric tube (3) for holding an excimer-forming
gas (5), a first central electrode (2) disposed within said tube (3), a second electrode
(4) arranged outside of said tube,
characterized in that said dielectric tube (3) has a UV fluorescent coating (6) on the outside.
2. VUV excimer lamp according to one of the preceding claims,
characterized in that said dielectric tube (3) is made of quartz glass.
3. VUV excimer lamp according to one of the preceding claims,
characterized in that said dielectric tube (3) is made of synthetic quartz glass.
4. VUV excimer lamp according to one of the preceding claims,
characterized in that said dielectric tube (3) is made of synthetic quartz glass without metal doping.
5. VUV excimer lamp according to one of the preceding claims,
characterized in that the UV fluorescent coating (6) is arranged between the dielectric (3) and the second
electrode (4).
6. VUV excimer lamp according to one of the preceding claims,
characterized in that said gas (5) consists essentially of Xe.
7. VUV excimer lamp according to one of the preceding claims,
characterized in that said gas (5) contains less than about 10 ppm of impurities.
8. VUV excimer lamp according to one of the preceding claims,
characterized in that said UV fluorescent coating (6) has phosphorus compounds.
9. VUV excimer lamp according to one of the preceding claims,
characterized in that said UV fluorescent coating (6) is a UV-C fluorescent coating.
10. Excimer lamp system with an VUV excimer lamp (1) according to one of the preceding
claims 1 to 9 and a power supply for supplying AC electric power to the first electrode
(2) and second electrode (4).
11. Photochemical unit with a VUV excimer lamp (1) according to one of the preceding claims
1 to 9.