Journal of Environmental Protection, 2012, 3, 695-699
doi:10.4236/jep.2012.38082 Published Online August 2012 (http://www.SciRP.org/journal/jep)695

High-Sensitivity Ozone Sensing Using 280 nm Deep
Ultraviolet Light-Emitting Diode for Detection of
Natural Hazard Ozone
Yoshinobu Aoyagi1, Misaichi Takeuchi1, Kaoru Yoshida1, Masahito Kurouchi1, Tsutomu Araki2,Yasushi Nanishi2, Hiroyasi Sugano3, Yumi Ahiko4, Hirotaka Nakamura5
1

Global Innovation Research Organization, Ritsumeikan University, Shiga, Japan; 2Faculty of Engineering Science, Ritsumeikan
University, Shiga, Japan; 3Hikari Technology; 4Miuraori Lab., Tokyo, Japan; 5Tokyo Metropolitan Industrial Technology ResearchInstitute, Tokyo, Japan.
Email: aoyagi@fc.ritsumei.ac.jp
Received February 22nd, 2012; revised April 3rd, 2012; accepted May 13th, 2012

ABSTRACT
Recently ozone is one of natural hazards which comes from cars, industry using ozone for sterilization of organic andinorganic materials and for water purification. So, ozone sensing becomes very important, and convenient and accurate
ozone sensor is required. A new high sensitivity ozone sensing system using an deep ultra-violet light emitting diode(DUV-LED) operated at the wavelength of 280 nm has been successfully constructed. The fabrication of diode operated
at 280 nm is much easier than that of DUV-LED operated at Hg lamp wavelength of 254 nm. The system is compact
and possible to sense the ozone concentration less than 0.1 ppm with an accuracy of 0.5% easily with low power
DUV-LED of around 200 micro Watts operated at 280 nm without any data processing circuit.
Keywords: Ozone Sensing; Deep Ultra Violet Light Emitting Diode; DUV-LED; High Sensitivity; Long Life; Compact

1. Introduction
The importance of ozone sensing has recently increased,because ozone is harmful gas which is generated fromindustrial use of ozone for sterilization and cleaning ofbiomaterials and semiconductor devises and also watersterilization. Furthermore, ozone is produced in the surface air by photochemical reactions involving unburned
fuel vapors and nitrogen oxides produced at high temperatures by car engines. So, the depletion of ozone isvery important. So, continuous, high-sensitivity easy detection of ozone is indispensable.
Ozone sensing is currently conducted by monitoring
the conductance change in thin-film-like semiconductors
containing ZnO [1,2], In2O3 [3,4]. Previous studies have
tried to measure ozone using a galvanic technique [5].
These devices have the advantages of being compact andvery cheap, but their lifetime is less than one year andtheir accuracy is very low at ±50%. Ozone sensing usinga Hg lamp was used for the purpose of solar-blind sensing in the aerospace industry [6,7]. Researchers have also
applied UV light to the chemiluminometric measurementof atmospheric ozone [8]. There have been attempts touse optical fibers for sensing [9]. However, there are few
reports on the determination of ozone concentration inCopyright © 2012 SciRes.

the air using Hg lamp systems, because of the difficulties
in accurate system construction with a high sensitivity
suitable for ozone monitoring and with a long life thatwould provide an accuracy of approximately ±0.5%. An
attempt was made to use a long-pass absorption chamber
to achieve high sensitivity [10]. However, the cost of thissystem was very high and it was unstable. The life of theHg lamp was only about one year and the size of the system was much larger than conventional sensors. Moreover, the Hg used in the lamp is a harmful metal, whichhas potentially detrimental environmental affects.
We recently developed a new type of ozone sensing
system using a low-power deep ultra violet light emitting
diode (hereafter DUV-LED) operated at the wavelengthof 280 nm as a light source, instead of an Hg lamp. Thissystem has the advantages of being very compact, having
a long lifetime, and being free from any harmful materials.
In this report, we present our experimental results anddemonstrate the utility of this system.

2. Experiments and Discussion
Figure 1 shows the typical spectra of a Hg lamp andDUV-LED operated at the wavelength of 280 nm. TheJEP

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High-Sensitivity Ozone Sensing Using 280 nm Deep Ultraviolet Light-Emitting
Diode for Detection of Natural Hazard Ozone

Figure 1. Spectrum of Hg lamp and DUV-LED operated at 280 nm.

size of Hg lamp is at least a few centimeters and the lamp
needs high voltage, whereas the size of the DUV-LED is
only 500 m and the voltage necessary is only 10 or 20
volt. The Hg lamp emits light at various wavelengths,
whereas the DUV-LED only emits light at a single wavelength of 280 nm. In case of DUV-LED, any wavelength
in DUV region can be chosen, depending on any different gases that might need to be monitored in addition toozone. Our case the wavelength of 280 nm was chosenbecause the LED quantum efficiency at this wavelength
region is much higher than that of LED operated at thewavelength of Hg lamp as shown in Figure 2. The big
advantages to use the diode operated at the wavelength of
280 nm is easiness of the device fabrication process andhigh device quality because of lower concentration of Alin AlGaN component than that operated at 254 nm. Thelarger the Al content in AlGaN, which is a main material
conducting DUV-LED, the lower the crystal quality andconductance between electrode and AlGaN are. The LED
was fabricated by ourselves using metal organic chemical
vapor phase epitaxy crystal growth technique.
Figure 3 shows the absorption band of ozone gas.
There are several main bands, which are referred to as
the Hartley band, Chappuls band, and the Wulf bands.
Light absorption occurs with each band, depending on
wavelength of light used. Depending on the requirements,
a longer absorption band can be used. In our experiment,
the absorption band around 260 nm was used. However,
the wavelength actually used in our experiment was 280
nm, because the external quantum efficiency of DUVLED was about 10 times larger than that at 254 nm of themain peak of the Hg lamp. However, the absorption coefficient of ozone at 280 nm is not very different fromthat at 254 nm. Thus, the total system efficiency using
the wavelength of 280 nm as ozone sensor, including
diode quantum efficiency and absorption coefficient ofCopyright © 2012 SciRes.

Figure 2. External quantum efficiency for various wavelengths of DUV-LED collected from papers published.

the light for ozone band, is much higher than the caseusing a 254 nm DUV-LED. In addition to this easy fabrication of the device of the 280 nm wavelength, the life
time is also much longer of more than ten time comparedto the 254 nm DUV-LED because of high quality materials for lower concentration of AlGaN. Actually the lifetime LED operated in blue region is more than 70000
hours which is much beyond the life of the Hg lamp. Atthis moment the lifetime of DUV-LED is not so longcompared to blue LED but it is expected to have such along life near future. At this moment the lifetime is about
5000 hrs if it will be operated at a few mW but it will beoperated a few hundreds micro watt the life is expectedJEPHigh-Sensitivity Ozone Sensing Using 280 nm Deep Ultraviolet Light-Emitting
Diode for Detection of Natural Hazard Ozone

to beyond easily 10,000 hrs.
Figure 4 illustrates the ozone sensing principle ofDUV-LED. Light emitted from the DUV-LED propagates a monitoring chamber with a length of 20 cm,
which is significantly shorter than the conventional

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length of a 50 cm monitoring chamber. In this figure thewavelength of light source of Hg lamp of 255 nm waswritten but in case of DUV-LED the wavelength was 280
nm. The gas sequence is shown in the same figure. Thesample gas and zero gas, which are completely filtered

Figure 3. Ozone absorption cross section.

Figure 4. Schematic diagram of ozone sensing system used. The zero gas and sample gas are alternatively fed into absorption
cell and estimated to evaluate ozone concentration.
Copyright © 2012 SciRes.

JEP

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High-Sensitivity Ozone Sensing Using 280 nm Deep Ultraviolet Light-Emitting
Diode for Detection of Natural Hazard Ozone

by a zero-gas filter, are alternately fed into the monitoring chamber at a set interval, until exhaustion. The lightemitted from the DUV-LED is absorbed in the monitoring chamber and detected by an AlGaN detector. Theexperiment has been done at RT, and the detected signal
was amplified using low noise amplifier. As a referenceof zero gas monitoring we used zero gas filter made by acompany. The zero gas filter has a capability of the reduction of ozone concentration of 1 20000 when theinlet gas concentration of 1 ppm. So, this ozone filter isenough to use zero gas standard for our experiment within experimental error. So, the zero gas of ozone after
through the filter is guaranteed. In this system at the beginning stage of 340 seconds the background ozone inatmosphere was observed. After the observation of background of ozone the ozone at monitoring position wasobserved 340 sec and this cycle are repeated to get accurate date. Finally the ozone concentration at the monitoring point is estimated by this measurement. Figure 5
shows raw data of monitoring results of ozone levels of
0.19 and 0.08 ppm under 200 μW power DUV-LED lightsource and a short monitoring chamber of 20 cm. Thisdata suggests that the ozone concentration less than 0.1ppm can easily be monitored by this short chamber andlow power of light source condition of 280 nm. The concentration of 0.1 ppm of ozone is the recommended
ACGIH-TLV-TWA value proscribed in the United States
as the safe limit for human ozone exposure. Figure 6
shows the output signal intensity as a function of ozone
concentration. Each point is an average of ten points
sampling. Ozone concentration is changed by ozone
generator and the ozone concentration was calibrated byother ozone monitoring system with the accuracy of0.5%. In our system we clearly find the sensitivity ofozone is much less than 0.1 ppm and is near 0.01 ppm
and the linearity of the detected signal as a function ofozone concentration was confirmed. The accuracy ofozone concentration of the observation system is ±0.5%
as shown in this figure. If we increase the DUV-LEDpower to 2 mW, which is now commercially available,
the detection limit will be improved much more.

3. Conclusion
We demonstrated a high-sensitivity ozone sensing system using a low-power DUV-LED operated at 280 nmFigure 5. Row data of signal under ozone gas and ozone freegas with a concentration of 0.19 ppm and 0.08 ppm.

Figure 6. Photo-sensing output signal as a function of ozone concentration.
Copyright © 2012 SciRes.

JEPHigh-Sensitivity Ozone Sensing Using 280 nm Deep Ultraviolet Light-Emitting
Diode for Detection of Natural Hazard Ozone

but not 254 nm Hg lamp light line. The sensitivity wasmuch less than 0.1 ppm and the accuracy of 0.5%. Thissystem is convenient and the size is small compared tothe ozone sensing system using Hg lamp. In addition theproposed wavelength 280 nm in this paper as DUV-LED
is very useful from the points of expectation of long lifetime of light source and high reliability and low voltage
operation. This system will contribute to depletion ofozone in nature generated from various reasons, includeing industry, car, etc.

REFERENCES
[1]

[2]

[3]

[4]

G. Kenanakis, D. Vernardou, E. Koudoumas, G. Kiriakidis and N. Katsarakis, “Ozone Sensing Properties ofZnO Nanostructures Grown by the Aqueous ChemicalGrowth Technique,” Sensors and Actuators, Vol. B124,
No. 1, 2007, pp. 187-191.
M. Suchea, N. Katsurakis, S. Christoulakis, S. Nikolopoulou and G. Kiriakidis, “Low Temperature Indium
Oxide Gas Sensors,” Sensors and Actuators B: Chemical,
Vol. 118, No. 1-2, 2006, pp. 135-141.
doi:10.1016/j.snb.2006.04.020
J. Li, Q. Li, J. V. Dyke and P. K. Dasgupta, “AtmosphericOzone Measurement with an Inexpensive and Fully
Automated Porous Tube Collector-Colorimeter,” Talanta,
Vol. 74, No. 4, 2008, pp. 958-964.
doi:10.1016/j.talanta.2007.08.002
R. Frycek, M. Jelinck, T. Kocourek, P. Fitl, M. Vrnata, V.

Copyright © 2012 SciRes.

699

Myskik and M. Vrbova, “Thin Organic Layers Preparedby MSPLE for Gas Sensor Application,” Thin Solid Films,
Vol. 495, No. 1-2, 2006, pp. 308-311.
doi:10.1016/j.tsf.2005.08.178[5]

S. Suzuki and K. Nagashima, “A Galvanic Solid-State
Sensor for Monitoring Ozone and Nitrogen Dioxide,”
Analytica Chimica Acta, Vol. 144, 1982, pp. 261-266.
doi:10.1016/S0003-2670(01)95542-4[6]

E. Trakhovsky, “Ozone Amount Determined by Transmittance Measurements in the Solar-Blind Ultraviolet
Spectral Region,” Applied Optics, Vol. 24, No. 21, 1985,
pp. 3519-3522. doi:10.1364/AO.24.003519[7]

L. M. Garrison, D. D. Doda and A. E. S. Green, “TotalOzone Determination by Spectroradiometry in the Middle
Ultraviolet,” Applied Optics, Vol. 18, No. 6, 1979, pp.
850-855. doi:10.1364/AO.18.000850[8]

T. Takayanagi, X.-L. Su, P. K. Dasgupta and R. W. Shaw,“Chemiluminometric Measurement of Atmospheric Ozonewith Photoactivated Chromotropic Acid,” Analytical Chemistry, Vol. 75, No. 21, 2003, pp. 5916-5925.

[9]

S. O’Keeffe, C. Fitzpatrick and E. Lewis, “An OpticalFiber Based Ultra Violet and Visible Absorption Spectroscopy System for Ozone Concentration Monitoring,”
Sensors and Actuators B: Chemical, Vol. 125, No. 2,
2007, pp. 372-378. doi:10.1016/j.snb.2007.02.023[10] E. M. Weinstock, C. M. Schiller and J. G. Anderson, “InSitu Stratospheric Ozone Measurements by Long PathUV Absorption: Developments and Interpretation,” Journal of Geophysical Research, Atmospheres, Vol. 91, No.
D4, 1986, pp. 5237-5248. doi:10.1029/JD091iD04p05237

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