CN112710643A - Method for improving detection sensitivity of photochemical gas sensor - Google Patents

Method for improving detection sensitivity of photochemical gas sensor Download PDF

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CN112710643A
CN112710643A CN202011490816.9A CN202011490816A CN112710643A CN 112710643 A CN112710643 A CN 112710643A CN 202011490816 A CN202011490816 A CN 202011490816A CN 112710643 A CN112710643 A CN 112710643A
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gas sensor
detection sensitivity
laser
gain medium
improving
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CN112710643B (en
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鲁雪纯
陈伟国
樊逢佳
杜江峰
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University of Science and Technology of China USTC
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    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
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Abstract

The invention discloses a method for improving the detection sensitivity of a photochemical gas sensor, which comprises the following steps: step one, a laser emitter of a photochemical gas sensor is used for emitting laser; step two, injecting the laser in the step one into a gain medium of the photochemical gas sensor to enable the laser to be in a population inversion state and generate stimulated radiation; step three, by using the stimulated radiation generated in the step two, when an optical signal generated by the stimulated radiation passes through the gas-sensitive material film in the population inversion state, an amplified spontaneous radiation signal is generated and emitted; and step four, collecting the amplified spontaneous emission signals to detect the response of the gain medium to the change of the environmental atmosphere. The method provides a new effective idea for improving the sensitivity of the photochemical gas sensor, the stimulated emission light obtained by the method has larger power, the spectral width is narrower than that of spontaneous emission, the collection efficiency is high, and the signal-to-noise ratio of the photochemical gas sensor and the detection sensitivity of the photochemical gas sensor are greatly improved.

Description

Method for improving detection sensitivity of photochemical gas sensor
Technical Field
The invention relates to the field of sensors and optical detection methods, in particular to a method for improving detection sensitivity of a photochemical gas sensor.
Background
The photochemical gas sensor is one of gas sensor systems, which is one of the latest developed gas sensors but one of the fastest developed technologies. Photochemical gas sensors are sensors that detect substances by using changes in the properties of propagating light caused by the changes in physical and chemical properties before and after the interaction between a sensitive layer and the substance to be detected, i.e. sensors that detect a target gas by using the optical properties of the gas. Compared with sensors based on other principles, the photochemical sensor has the advantages of good safety, long-distance detection, high resolution, low working temperature, low power consumption, continuous real-time monitoring, easy conversion into electric signals and the like, so the photochemical sensor and the method for improving the detection sensitivity thereof are widely concerned.
Photochemical gas sensors use the interaction between light and a substance, such as: absorption, dispersion, transmittance change, fluorescence quenching and the like to monitor the interaction between the substance to be detected and the sensor. The optical detection means of a common photochemical sensor is a fluorescence detection method, which generally utilizes the principle of spontaneous emission, and atoms are transited under the action of a vacuum field, and during the process, auger non-radiative recombination is easily generated during spontaneous emission electron-hole recombination. When the exciton number is changed from 0 to a smaller range, the Auger non-radiative recombination effect is weaker, and the spontaneous emission is approximately linearly increased along with the change of the average exciton number; when the number of excitons is greater than 1, auger non-radiative recombination phenomenon is severe due to the interaction of electrons between excitons, so that fluorescence no longer increases as the number of excitons increases. It can be seen that the sensitivity of spontaneous emission to exciton number response is low, and the conventional fluorescence detection method is no longer suitable for improving the sensitivity of the photochemical gas sensor when the exciton number is greater than 1. Therefore, a new method for improving the detection sensitivity of the photochemical gas sensor is needed.
Disclosure of Invention
Technical problem to be solved
In the process of implementing the present disclosure, the applicant finds that, by using the gain principle of the stimulated radiation, when an optical signal emitted by a laser passes through a quantum dot thin film in a population inversion state, Amplified Spontaneous Emission (ASE for short) is formed, the ASE signal can generate exponential response to the weak change of the detection environment of the photochemical gas sensor, and the ASE signal can be used to improve the detection sensitivity of the photochemical gas sensor. The present disclosure thus proposes an application of the stimulated emission principle and a method for improving the detection sensitivity of a sensor to at least partially solve the above-mentioned technical problems.
(II) technical scheme
In order to achieve the above object, the present invention provides a method for improving the detection sensitivity of a photochemical gas sensor, comprising:
step one, a laser emitter of a photochemical gas sensor is used for emitting laser;
step two, injecting the laser in the step one into a gain medium of the photochemical gas sensor to enable the laser to be in a population inversion state and generate stimulated radiation;
step three, by using the stimulated radiation generated in the step two, when an optical signal generated by the stimulated radiation passes through the gas-sensitive material film in the population inversion state, an amplified spontaneous radiation signal is generated and emitted;
and step four, collecting the amplified spontaneous emission signals to detect the response of the gain medium to the change of the environmental atmosphere.
Optionally, the wavelength of the laser in the first step is 330nm to 360 nm.
Optionally, the wavelength of the laser in the first step is 355 nm.
Optionally, the gain medium material in the first step is CdSe/CdS, GaAs, AlGaAs, Nd: YAG or Yb: YAG.
Optionally, the gas sensitive material film comprises a quantum dot film.
Optionally, the amplified spontaneous emission is exponentially responsive to a change in a detection environment of the photochemical gas sensor.
Optionally, detecting the response of the gain medium to changes in the ambient atmosphere comprises:
calculating the stimulated emission intensity according to the light intensity of the amplified spontaneous emission signal and the gain coefficient of the gain medium:
Figure BDA0002837999220000021
wherein z is the distance over which light travels on the gain medium; i is0Initial intensity at z-0; e is the natural logarithm, with a value of 2.718; g0Is a gain factor.
(III) advantageous effects
The invention provides an application of a stimulated radiation principle and a method for improving the detection sensitivity of a sensor. The invention provides a new effective idea for improving the sensitivity of the photochemical gas sensor, and the stimulated radiation light obtained by the method has larger power, narrower spectrum width than spontaneous radiation, certain directivity and high collection efficiency, thereby achieving the effect of greatly improving the signal-to-noise ratio of the photochemical gas sensor and the detection sensitivity of the photochemical gas sensor.
Drawings
FIG. 1(a) is a graph showing the response of ASE signal and PL signal to the change in the number of excitons;
FIG. 1(b) is a graph comparing the intensity changes of ASE signal and PL signal under the same conditions;
FIG. 2 is a schematic diagram of an experimental setup for detecting changes in the gain medium of quantum dots;
FIG. 3(a) is a graph showing a variation in ASE signal intensity in a dry/wet nitrogen atmosphere;
FIG. 3(b) is a waveform diagram showing the variation in ASE signal intensity under dry/wet nitrogen atmosphere conditions;
FIG. 4(a) is a plot of the change in PL signal intensity under dry/wet nitrogen atmosphere;
FIG. 4(b) is a waveform diagram showing the change in PL signal intensity under dry/wet nitrogen atmosphere conditions.
Detailed Description
In order that the objects, technical solutions and advantages of the present invention will become more apparent, the present invention will be further described in detail with reference to the accompanying drawings in conjunction with the following specific embodiments. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity, and like reference numerals designate like elements throughout.
Through in-depth research, the amplified spontaneous radiation enables the quantum dots to generate optical gain when the average exciton number in the quantum dots is slightly changed, and even if the exciton number generated by the quantum dots is slightly changed, the light intensity can generate exponential response under the influence of the optical gain, so that the optical gas sensor has high detection sensitivity.
Based on the principle, the invention applies the stimulated radiation principle to the photochemical gas sensor, so that the gas-sensitive material in the photochemical sensor, namely the quantum dot, generates amplified spontaneous radiation. Even when the detection environment induces weak change of exciton number, the amplified spontaneous radiation can enable the optical signal to respond exponentially to the weak change. Therefore, the application of the stimulated radiation greatly improves the sensitivity of the optical response detection method of the gain medium to the environmental change in the optical gas sensor.
The application of the stimulated emission principle to the optical gas sensor is described in detail below with reference to the embodiments.
The gain factor for the percentage increase in light intensity after light has passed through the activated species per unit length is:
Figure BDA0002837999220000041
where z is the distance over which light travels over the gain medium, and I (z) is the intensity of light at z in the direction of light propagation.
The stimulated absorption versus stimulated radiation is:
Figure BDA0002837999220000042
wherein n is1Is at a conduction band energy level E per unit volume1Atomic number of (2), n2Is at a conduction band energy level E per unit volume2T is the transition time, dn12Is caused by stimulated absorption transition in dt time in unit volume1To E2Atomic number of transition, dn21Is caused by stimulated radiation transition in dt times in a unit volume2To E1Atomic number of transition, h is Planck constant 6.62X 10-34J.S.v. the frequency of the radiation field, W21For stimulated emission transition probability, W12For stimulated absorption transition probability, B21Rho (v) is the black body radiation monochromatic energy density for the stimulated absorption transition einstein coefficient.
When conduction band energy level E1Statistical weight f of1And conduction band energy level E2Statistical weight f of2When equal, there are:
g∝B21hv(n2-n1)dz
if (n)2-n1) Is not changed with z, the gain coefficient g is a constant g0At this time I0For the initial intensity at z-0, then there is an exponential amplification response formula for the optical signal:
Figure BDA0002837999220000043
where e is the natural logarithm, and its value is 2.718.
According to the research of Bell laboratory in 1973 on the optical gain of semiconductors, when the length of an excited region is l, the intensity I of excited radiation is obtainedASEAnd intensity of spontaneous emission ISPONTThe variation of the intensity is as follows:
Figure BDA0002837999220000051
wherein a is a loss factor.
As can be seen from the above formula, the intensity of the stimulated radiation IASECompared with the spontaneous radiation intensity I in the traditional fluorescence detection methodSPONTAn exponential amplification is obtained in the numerical value.
As shown in FIGS. 1(a) and 1(b), the response degree of the ASE signal according to the number of excitons is significantly better than that of the PL signal in the conventional fluorescence detection method. In particular, the amount of the solvent to be used,
as shown in FIG. 1(a), the vertical axis
Figure BDA0002837999220000052
Representing the ground state bleaching signal, horizontal axis<N>Representing the number of excitons, wherein a PL curve is the response degree of a PL signal along with the change of the number of excitons in the traditional fluorescence detection method, a sti curve is the response degree of an ASE signal along with the change of the number of excitons, and the value is represented by a gain coefficient formula:
Figure BDA0002837999220000053
(where OD is the absorbance of the gain medium under laser light) can be obtained, and the gain increases with the number of excitons and eventually tends to saturate. As can be seen from FIG. 1, the ASE signal based on the stimulated emission principle is exponentially amplified along with the increase of the number of the lasers, and the response degree of the ASE signal is obviously superior to the quasi-linear optical response degree of the PL signal in the traditional fluorescence detection method.
As shown in fig. 1(b), the gain coefficient g is set to 1n10-OD, and the ASE signal and the PL signal are normalized, so that the degree of change of the intensity of the ASE signal to the intensity of the PL signal with the number of excitons becomes more remarkable, and the intensity ratio of the two increases with the number of excitons.
The following examples demonstrate, by way of experiments, that the amplified spontaneous emission generated by applying the stimulated emission principle can achieve the effect of improving the detection sensitivity of the photochemical gas sensor.
The first embodiment is an ASE signal response effect test, which comprises the following steps:
s11: laser with the wavelength of 355nm is emitted by a laser emitter and is injected into a CdSe/CdS core-shell structure quantum dot gain medium (the quantum dot is low in energy level degeneracy and threshold and easy to be in a layout number inversion state), stimulated radiation is generated, and an ASE signal is emitted.
S12: the detection environment of the optical gas sensor is simulated by introducing nitrogen.
Fig. 2 is a schematic diagram of an experimental apparatus for detecting the change of the gain medium of the quantum dot, which adjusts the environmental atmosphere (dry/wet nitrogen) on the surface of the gain medium in the sealed box by controlling the opening and closing of the air valve 1 and the air valve 2, focuses 355nm laser on the surface of the gain medium in the sealed box through the adjustable attenuator, the plano-convex lens, the cylindrical lens and the optical slit, and observes the change of the ASE signal and the PL signal generated by the gain medium.
As shown in fig. 2, the gas valve 1 is opened, the gas valve 2 is closed, dry nitrogen is introduced to the surface of the quantum dot, so that the quantum dot gain medium is in the environment atmosphere of the dry nitrogen, and the change of the quantum dot gain medium at this time is collected.
S13: and closing the air valve 1, opening the air valve 2, introducing wet nitrogen to the surface of the quantum dot, enabling the quantum dot gain medium to be in the environment atmosphere of the wet nitrogen, and collecting the change of the quantum dot gain medium at the moment.
S14: the steps S12 and S13 are repeated in a loop sequentially, and the change of the quantum dot gain medium at all times is collected, so as to obtain the ASE signal response graphs shown in fig. 3(a) and 3 (b).
As can be seen from fig. 3(a) and 3(b), the ASE signal response of the quantum dot gain medium in the environment atmosphere with alternating dry/wet nitrogen exhibits strong and weak alternating regularity.
Example two is the effect of the response of the measured fluorescent PL signal in the probing environment of example one, the assay comprising:
s21: the laser emitter is used for emitting laser with the wavelength of 355nm and emitting the laser into the CdSe/CdS core-shell structure quantum dot gain medium to generate spontaneous radiation and emit a PL signal.
S22: step S14 is repeated to collect the changes of the quantum dot gain medium at all times, and the PL signal response graphs shown in fig. 4(a) and 4(b) are obtained.
As can be seen from fig. 4(a) and 4(b), the PL signal response of the quantum dot gain medium in the ambient atmosphere with alternating dry and wet nitrogen gas changes hardly significantly.
As can be seen from FIGS. 3(a) to 4(b), the detection of the humidity change in the environment of the CdSe/CdS quantum dot gain medium by using the ASE signal generated by the stimulated emission principle of the present invention has higher sensitivity than the detection of the PL signal generated by the conventional fluorescence spontaneous emission principle.
It should also be noted that unless steps are specifically described or must occur in sequence, the order of the steps is not limited to that listed above and may be varied or rearranged as desired. The embodiments described above may be mixed and matched with each other or with other embodiments based on design and reliability considerations, i.e., technical features in different embodiments may be freely combined to form further embodiments.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (7)

1. A method of increasing the detection sensitivity of a photochemical gas sensor comprising:
step one, a laser emitter of the photochemical gas sensor is used for emitting laser;
step two, injecting the laser in the step one into a gain medium of the photochemical gas sensor to enable the laser to be in a population inversion state and generate stimulated radiation;
thirdly, generating and emitting amplified spontaneous emission signals when the optical signals generated by the stimulated radiation pass through the gas-sensitive material film in the population inversion state by using the stimulated radiation generated in the second step;
and step four, collecting the amplified spontaneous emission signals to detect the response of the gain medium to the change of the environmental atmosphere.
2. The method for improving the detection sensitivity of an optical chemical gas sensor according to claim 1, wherein the wavelength of the laser in the first step is 330nm to 360 nm.
3. The method for improving the detection sensitivity of an optical chemical gas sensor according to claim 2, wherein the wavelength of the laser in the first step is 355 nm.
4. The method for improving the detection sensitivity of an optical chemical gas sensor according to claim 1, wherein the gain medium material in the first step is CdSe/CdS, GaAs, AlGaAs, Nd: YAG or Yb: YAG.
5. The method for improving the detection sensitivity of an optical chemical gas sensor according to claim 1, wherein said gas sensitive material film comprises a quantum dot film.
6. The method of improving the detection sensitivity of an actinic gas sensor according to claim 1, wherein said amplified spontaneous emission is exponentially responsive to changes in the detection environment of said actinic gas sensor.
7. The method for improving the detection sensitivity of an optical chemical gas sensor according to claim 1, wherein said detecting the response of said gain medium to the change of the ambient atmosphere comprises:
calculating stimulated emission intensity according to the light intensity of the amplified spontaneous emission signal and the gain coefficient of the gain medium:
Figure FDA0002837999210000011
wherein z is the distance over which light travels on the gain medium; i is0Initial intensity at z-0; e is the natural logarithm, with a value of 2.718; g0Is a gain factor.
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