JP2969857B2 - Optical gas detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical gas detection device for detecting NO ₂ gas and NO gas using a thin film containing an organic dye molecule as a gas-sensitive body.

(Prior Art) As a conventional gas detection device, a catalytic combustion type or a semiconductor type has predominantly been used. In recent years, a gas detection device using light, such as an optrode disclosed in JP-A-62-35246, has been proposed. Furthermore, it is known that certain organic dye molecules interact with an oxidizing or reducing gas with a certain degree of selectivity and change in electrical or optical properties, such as changes in the electrical properties of phthalocyanine. the utilized NO _x, it is also proposed to apply to SO _x gas detecting device.

(Problems to be Solved by the Invention) By the way, gas sensors using light such as Optrode have complicated gas sensing parts, require large lasers as light sources, or have photomultipliers in the light receiving parts. Using a tube was not an easy thing. Also, even when organic dye molecules are used, a stable gas detection device capable of repeatedly detecting gas by simple means has not yet been known as a practical gas detection device.

 The present invention has been made under such circumstances.

An object of the present invention is to provide a small-sized optical gas detector for measuring NO gas or NO ₂ gas, which has good sensitivity, high response speed, and can be used in a wide concentration range.

(Means for Solving the Problems) An optical gas detecting device according to the present invention is a gas detecting element comprising a light emitting element, a light receiving element, and a thin film containing an organic dye that emits fluorescence or phosphorescence by light from the light emitting element. When,
Optical gas detection means having a filter for separating fluorescence or phosphorescence emitted from the thin film containing the organic dye,
Gas conversion means for converting the NO gas in the NO _x gas which is the gas to be detected into NO ₂ gas; and the NO _x gas which is the gas to be detected and the gas to be detected which is converted by the gas conversion means, selectively. Means for leading to the gas sensing element, and the detected NO
and NO ₂ amount in _x gas, on the basis of the NO ₂ content of the detected gas which is converted by the gas conversion unit, characterized in that it comprises means for quantifying NO gas in said detection target gas.

The gas detection element used in the optical gas detection device of the present invention is formed of a thin film containing an organic dye, and has a property of emitting fluorescence or phosphorescence by light from the light-emitting element. Can be used in a form provided with a thin film containing. This thin film is composed of a gas to be detected,
That the presence of the converted NO ₂ gas from the NO ₂ gas and NO gas, fluorescence or phosphorescence intensity changes reversibly. Therefore, the gas to be detected can be detected by measuring the change in the intensity of fluorescence or phosphorescence generated from the thin film.

In particular, a gas sensing element composed of a thin film containing a J-aggregate of a squarylium dye is used as an organic dye, and NO ₂
When measuring gas, the gas can be detected as it is, and when measuring NO gas, NO gas can be detected with high sensitivity by converting NO gas to NO ₂ gas. One of the reasons is that the excited state generated by the absorption of light in the J-aggregate
It is thought that the region which can be covered as a trapping site in the excited state generated by the absorption of the NO ₂ gas became larger by being able to move to. As the squarylium dye, those represented by the general formula (I) can be advantageously used.

(In the formula, X and Y each represent a chromophore.) In the general formula (I), examples of the chromophore represented by X and Y include the following.

[Wherein, R ₁ and R ₂ are the same or different and are each a hydrogen atom, C _n H _{2n + 1} , C _n H _2n OH, C _n H _2n-1 , C _n H _2n-3
(Where n is 1 to 20), a chlorine atom, a fluorine atom or a bromine atom, and R ₃ is a hydrogen atom, hydroxylated, C _n H _{2n + 1} (however,
n represents a methoxy group, a fluorine atom, a chlorine atom or a bromine atom, R ₄ represents a hydrogen atom, a hydroxyl group, C _n H _{2n + 1} (where n is 1 to 20), a methoxy group; Z is C (CH ₃ )
₂ , O, S or Se is shown. Specific examples of the squarylium dye include Japanese Patent Application No. 63-63.
No. 69666 can be mentioned.

In the optical gas detection device of the present invention, a semiconductor laser device, an LED, or the like can be used as a light emitting device used as an excitation light source for generating fluorescence or phosphorescence from a thin film as described above.

A filter for separating the fluorescence or phosphorescence from the excitation light is disposed in an optical path between the gas detection element and the light receiving element. As this filter, a filter which cuts light emitted from the light emitting element and mainly transmits fluorescent light or phosphorescent light emitted from the gas detecting element is used. Further, it is preferable to use a filter having a characteristic of cutting light having a longer wavelength than fluorescent light or phosphorescent light emitted from the gas detection element.

In the present invention, when a component other than light having a wavelength necessary for excitation is emitted from the light emitting element to be used, a filter for cutting the component may be further used. That is, a filter having a characteristic of mainly transmitting light near the main emission wavelength emitted from the light emitting element and mainly cutting light other than light near the main emission wavelength emitted from the light emitting element is provided between the light emitting element and the gas detection device. May be arranged in the optical path. In that case, it is preferable to arrange the filter so that light incident on the filter is incident on the filter surface at an angle to a direction perpendicular to the filter surface.

(Operation) According to the optical gas detection device of the present invention, the reversible color change or fluorescence or phosphorescence intensity change of the thin film is measured by contacting the gas containing the organic dye of the gas detection element with the gas to be detected. Thus, the test gas can be detected. That is, the excitation light emitted from the light emitting element reaches the thin film containing the organic dye of the gas detection element, where it excites the organic pigment to generate fluorescence or phosphorescence. In that case, the thin film containing the organic pigment comes in contact with a very low concentration (several ppb) of NO ₂ gas,
The intensity of the fluorescence or phosphorescence generated from the gas detection thin film changes greatly and reversibly. Therefore, if the change in the intensity is guided to the light receiving portion through an optical filter so as to receive only the fluorescence or phosphorescence generated from the gas detection thin film, the NO ₂ gas can be detected with extremely high sensitivity.

On the other hand, this organic dye thin film does not change its fluorescence or phosphorescence much depending on the NO gas, and its sensitivity is 1/10 or less of the sensitivity to NO ₂ gas.

Therefore, when the generally NO _x gas present as it is introduced to the light detecting portion can detect the NO ₂ gas which is one of the main components. On the other hand, NO gas is another major component of the NO _x gas reacts readily with oxygen in the air at room temperature
It is known to be NO ₂ gas. In oxygen (O ₂ ) gas and ozone (O ₃ ) gas, they react faster to become NO ₂ gas. Accordingly, NO and the detected NO _x gas by pouring the gas detector comprising an optical system and an organic dye thin film by reacting with air or oxygen or ozone gas, which is converted to NO ₂ gas and NO ₂ that was originally present the concentration of the sum of both ₂ gas as in the case for the NO ₂ gas can be detected with very high sensitivity. From these values, N in the detected NO _x gas
Both the O ₂ gas concentration and the NO gas concentration can be detected with extremely high sensitivity.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a basic configuration diagram of an optical part of an optical gas detection device according to the present invention. In the figure, 1 is a light emitting element, 2 is a lens, 3 is a gas detecting element made of a thin film containing an organic dye, 4
Denotes a filter for cutting excitation light, and 5 denotes a light receiving element.

Excitation light emitted from the light emitting element 1 is condensed by the lens 2 and irradiated on the gas detection element 3. As a result, fluorescence or phosphorescence is generated from the thin film of the gas detection element 3. The generated fluorescent light or phosphorescent light passes through the filter 4 and the light receiving element 5.
, And is converted into an electric signal by an electric circuit (not shown). In this case, when the NO ₂ gas comes into contact with the gas detection element 3, the intensity of fluorescence or phosphorescence emitted from the gas detection element 3 changes, and the gas concentration can be detected as an electric signal.

In the present invention, the gas detecting element 3 is, for example, a thin film containing an organic dye formed on a substrate made of glass or the like. When irradiated with light in the range of 600 to 760 nm, fluorescence or phosphorescence having a peak near 770 nm is obtained. Can be advantageously used.

In that case, as the light emitting element 1, an LED or a semiconductor laser element having a main emission wavelength in the range of 600 to 760 nm is preferably used, and these can be used as a small excitation light source.

The light receiving element 5 must be sensitive to fluorescence or phosphorescence having a peak wavelength near 770 nm.

The lens 2 is used to prevent the light emitted from the light emitting element 1 from diverging and to effectively collect the light on the gas detecting element 3, and to increase the intensity of fluorescence or phosphorescence emitted from the gas detecting element 3. It is valid. The lens 2 may be formed integrally with the light emitting element 1.

The filter 4 functions to prevent the excitation light emitted from the light emitting element 1 from being reflected or scattered by the gas detection element 3 and entering the light receiving element 5. Therefore, even when the light receiving element 5 has sensitivity to the excitation light, the excitation light and the scattered light are prevented by the filter 4 so that the fluorescence or the phosphorescent light of the light entering the light receiving element 5 can be prevented. The ratio increases, and a signal with less noise can be obtained.

In order to effectively collect the fluorescent light or the phosphorescent light, a lens may be placed in front of the light receiving element 5 or the filter 4, or an integrated lens and light receiving element may be used.

The gas detecting means 10 configured as described above is connected to the gas converting means 11 for converting NO gas to NO ₂ gas, and the gas to be measured and the air ( Or O ₂ or O ₃ gas)
Is introduced into the gas detecting means 10, and the concentrations of the NO gas and the NO ₂ gas are measured.

In the optical gas detection device of the present invention, in order for the light-receiving element 5 to effectively receive the fluorescence or phosphorescence emitted from the gas detection element 3, the light-emitting element 1, the lens 2, the gas detection element 3, the filter 4, the light-receiving element Although it is necessary to arrange them in the order of 5, it is desirable to arrange these parts as close as possible in order to make the device as small as possible and obtain a large electric signal. In that case, in order to prevent the excitation light from entering the light receiving element 5, the light receiving element 5
It is desirable not to dispose the excitation light in the direction where the excitation light is specularly reflected by the gas detection element 3. As a specific arrangement, the filter 4 and the light receiving element 5 are integrated and arranged vertically with respect to the gas detection element 3, while the light emitting element 1 and the lens 2 are integrated and aligned with respect to the vertical direction. It is preferable to arrange at an appropriate angle (several degrees to several tens degrees).

The light emitted from the light emitting element 1 acts as excitation light.
In addition to light in the wavelength range of 0 to 760 nm, light having a longer wavelength may be included. For example, in a light emitting element using a GaAs-based material, photoluminescence having a small peak near 890 nm is slightly emitted together with light having a main emission wavelength having a peak in the range of 600 to 760 nm. Although the peak intensity of this light is one hundredth or less of the peak intensity of the main emission wavelength, it can be a noise when measuring fluorescence or phosphorescence. In order to eliminate such noise light, in the present invention, the filter 4 is provided with a band-pass filter having a property of transmitting only a fluorescent or phosphorescent component near 780 nm and cutting short and long wavelength sides. Filter or
Alternatively, a filter may be additionally inserted to cut off light having a wavelength longer than the fluorescence or phosphorescence component around 780 nm. In the latter case, the filter for cutting off the light on the longer wavelength side to be added may be provided at any position in principle in the optical path between the light emitting element 1 and the light receiving element 5, but from the viewpoint of space. Is preferably provided at the position shown in FIG. That is, the filter 6 that cuts light on the long wavelength side is
It is arranged between the lens 2 and the gas detection element 3. In particular, when a semiconductor laser element is used as the light emitting element, the filter 6 is not arranged perpendicular to the excitation light, but is arranged at a slight angle as shown in FIG. It is desirable that the light reflected on the surface does not return to the emitting section of the semiconductor laser device. The second
In the figure, other symbols have the same meaning as in FIG.

In the case of FIG. 1, the entire gas detection system is housed in a small box to form an optical gas detection device. in this case,
Gas detection is performed by placing the entire gas detection system in the gas to be detected. However, it takes a little time for the gas to be detected to fill the entire box, and the response speed of the detection becomes slow. Therefore, it is preferable to provide a gas introducing member around the gas detection element so that the gas flows only around the gas detection element.

FIG. 3 shows such a case. By providing the gas introducing member 7 around the gas detecting element 3 and minimizing the dead space, the response speed can be increased. Further, since the light emitting element 1, the lens 2, the filter 4, the light receiving element 5 and the like are separated from the gas to be detected, improvement in reliability can be expected. It goes without saying that at least a part of the introduction member 7 needs to transmit the excitation light and the signal light.

FIG. 4 shows an optical gas detection device according to the present invention.
FIG. 3 is a basic configuration diagram of a portion that converts gas into NO ₂ gas. In the figure, 8 is a four-way cock and 9 is a gas mixer.

In FIG. 4 (a), the gas to be detected is a gas mixer 9
And mixed with a certain amount of air or oxygen or ozone in a mixer, and the NO gas is converted into NO ₂ gas. In this state, the concentration of the sum of the NO gas and the NO ₂ gas in the detected gas is measured. On the other hand, in the state shown in FIG. 4 (b), the gas to be detected is introduced into the optical sensor without passing through the gas mixing system, so that only the NO ₂ gas concentration in the gas to be detected is measured.
By converting the dilution ratio with the mixed gas, both the concentrations of the NO gas and the NO ₂ gas in the detected gas can be measured with the same sensitivity.

When mixing with the same amount of air or pure oxygen or air containing 10% ozone, the gas mixture system has a permeation time of about 30 seconds for air, about 10 seconds for pure oxygen, and about 10 seconds for air containing ozone. In 5 seconds, the NO gas was sufficiently converted to NO ₂ gas. Here, it is necessary that the gas to be mixed contains NO ₂ gas only at a negligible concentration as compared with the gas to be detected.

 Next, more specific examples will be described.

(Example 1) Squarylium dye represented by the following formula And arachiic acid (C ₁₉ H ₃₉ COOH) were dissolved in chloroform at a molar ratio of 1: 1 to prepare a solution having a concentration of about 8 × 10 ⁻⁴ M. Using this solution, a film was formed by an LB film forming method.
As a result, a gas detection element comprising a J-aggregate of a squarylium dye was obtained. That is, about 200 μl was spread on the water surface, and the gas sensing element was obtained by forming a gas-sensitive thin film on the glass substrate by raising and lowering the air-water interface of the glass substrate.

A commercially available semiconductor laser device having a peak wavelength around 670 nm was used as a light emitting device, and used as an excitation light source. A plastic lens for collecting this light was provided in front of the semiconductor laser device. A commercially available silicon photodiode was used as the light receiving element, and an excitation light cut filter was attached in front of it. The excitation light cut filter was formed by depositing an interference film on a color glass filter, and cut the excitation light on the shorter wavelength side than around 720 nm. These components were arranged as shown in FIG. That is, the excitation light cut filter and the silicon photodiode are substantially perpendicular to the gas detection element,
It was arranged at a distance of 5 to 10 mm from the thin film surface of the gas detection element.

The semiconductor laser element and the lens were arranged such that the excitation light was incident on the gas detection element at an angle of about 60 ° from the vertical direction. These were black-processed inside together with a semiconductor drive circuit and a photodiode drive circuit, and were placed in a box provided with a gas inlet to produce an optical gas detection means 10. The gas conversion means 11 for converting NO gas into NO ₂ gas is a fourth gas conversion means.
As shown in FIGS. 1A and 1B, the apparatus comprises a four-way cock 8 for switching the gas flow and a gas mixer 9.

In this optical gas detection device, when the semiconductor laser device is turned on, the excitation light is applied to the gas detection element, and the fluorescence or phosphorescence emitted therefrom is received by the photodiode,
A 10 ^-9 A current flowing through the photodiode could be extracted as a 1 V voltage signal by an electric circuit. In this state, when a mixed gas containing NO gas and NO ₂ gas at a concentration of 0.01 to 100 ppm is introduced from the gas inlet, the four-way cock is brought to the concentration of NO ₂ gas in the state of FIG. In the condition (2), the signal voltage changes according to the concentration of the sum of the _two, and by converting the concentration diluted by the mixer, the concentrations of the NO ₂ gas and the NO gas can be separated and quantitatively measured.

(Example 2) An optical gas detector was manufactured using the same components as in Example 1 except for the excitation light cut filter. As the excitation light cut filter, a bandpass filter transmitting light in the vicinity of 720 nm to 850 nm was used. Place in much the same way as in Example 1, the signal level by non shed NO _x gas was adjusted to be almost the same as in Experimental Example 1. Flowing NO gas and NO ₂ gas sequentially switches the four-way cock in this state, the signal voltage changes depending on the concentration of NO gas and NO ₂ gas, to separate the NO gas and NO ₂ gas concentration quantitatively I was able to measure. The change in the signal voltage in this case was larger than in the case of the first embodiment. That is, it was confirmed that the S / N ratio was improved by cutting off the light having a peak near 890 nm.

(Example 3) As a light emitting element, a lens, a gas detection element, an excitation light cut filter, and a light receiving element, those similar to those in Example 1 were used and arranged in substantially the same manner as in Example 1. However, 800n
An infrared cut filter for cutting light on the wavelength side from the vicinity of m was provided in front of the lens. In this case, the infrared cut filter was inclined so that the excitation light had an incident angle of about 20 ° with respect to the infrared cut filter. Signal level by non shed NO _x gas was adjusted to be almost the same as in Example 1. Flowing NO gas and NO ₂ gas sequentially switches the four-way cock in this state, the signal voltage changes depending on the concentration of NO gas and NO ₂ gas, to separate the NO gas and NO ₂ gas concentration quantitatively I was able to measure. The change in the signal voltage in this case was larger than in the case of the first embodiment. That is, 890 nm
It was confirmed that the S / N ratio was improved by cutting light having a peak in the vicinity.

(Example 4) A test was performed using the same material and method as in Example 1 except that the gas detection element was placed in a gas introduction member made of transparent glass. When NO gas and NO ₂ gas flow by sequentially switching the four-way cock in the gas introduction member, the signal voltage changes according to the concentration of NO gas and NO ₂ gas, respectively, and NO gas and NO
_{The two} gas concentrations were separated and measured quantitatively. The response speed in this case was one tenth or less of that of the first embodiment.

(Example 5) Instead of a semiconductor laser element, an LED having a lens-shaped tip having a peak wavelength around 660 nm was used as a light source for excitation, and a photodiode with a lens was used as a light receiving element. Other gas detection elements, the excitation light cut filter, and the arrangement thereof were the same as those in Example 1.

These were black-processed inside together with the LED drive circuit and the photodiode drive circuit, and placed in a box provided with a gas inlet to produce an optical gas detection device.

When the LED is turned on for this optical gas detector,
The excitation light was applied to the gas detection element, and the fluorescence or phosphorescence emitted therefrom was received by the photodiode, and could be extracted as a voltage signal. In this state, when 0.01 to 100 ppm of NO and NO ₂ gas were introduced from the gas inlet, respectively, the signal voltage changed according to the concentration of NO _x , and the respective gas concentrations could be separated and measured quantitatively.

(Effect of the Invention) As described above, the optical gas detection device of the present invention includes a gas containing an organic dye in an optical path between a light emitting element and a light receiving element, and emitting fluorescence or phosphorescence by light emitted from the light emitting element. Since it has a configuration in which the detection element and the filter are sequentially arranged, gas detection can be easily performed using reversible physical and scientific changes caused by interaction with the gas to be detected. Further, the gas to be detected can be quantitatively detected by utilizing the reversible physical and chemical changes. By adding a gas mixer, not only NO ₂ gas but also NO gas can be measured with very high sensitivity.

The optical gas detection device of the present invention has optical sensitivity, stability,
Excellent response speed and can be used in a wide concentration range. In addition, since it is easy to manufacture and advantageous in terms of cost and environment, it can be applied to a very wide range. Furthermore, since it utilizes light, it is resistant to electrical, magnetic and chemical disturbances.

Since the thin film of the gas detecting element of the present invention changes its electrical characteristics and the like with a change in color, the gas detecting element of the present invention can also be used as a gas-sensitive element of a conventional electric gas sensor.

In addition, the optical gas detection device of the present invention uses a semiconductor laser or an LED as an excitation light source, and can use a photodiode as a light receiving element. The optical gas detector is advantageous in terms of miniaturization, cost reduction, and reliability.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a basic configuration of an optical gas detection device of the present invention, FIG. 2 is a configuration diagram showing another basic configuration of an optical gas detection device of the present invention, and FIG. FIG. 4 is another basic configuration diagram of the gas detection device of the type. FIG. 4 shows the basic configuration of the gas conversion means. 1 ... light-emitting element, 2 ... lens, 3 ... gas detection element,
4 filter 5 light receiving element 6 filter 7 gas introducing member 8 four-way cock 9 gas mixer 10 optical gas detecting means 11 gas conversion means.

Claims (1)

(57) [Claims] 1. A gas detecting element comprising a light emitting element, a light receiving element, a thin film containing an organic dye which emits fluorescence or phosphorescence by light from the light emitting element, and a fluorescent or phosphorescent light emitted from the thin film containing the organic dye. an optical gas sensing means and a filter to separate, NO _x is gas to be detected
Gas conversion means for converting NO gas in the gas to NO ₂ gas,
The NO _x gas is the gas to be detected and, means for directing selectively the gas sensing element the gas to be detected which has been converted by said gas conversion unit, and NO ₂ amount of the object to be detected NO _x gas, the gas NO _{2 in the} gas to be detected converted by the conversion means
An optical gas detection device, comprising: means for quantifying NO gas in the gas to be detected based on the amount.