WO2008151349A1

WO2008151349A1 - Sensor for the detection of gases

Info

Publication number: WO2008151349A1
Application number: PCT/AT2008/000216
Authority: WO
Inventors: Georg Jakopic; Elke Kraker; Bernhard Lamprecht; Anja Haase; Christian Konrad; Stefan Köstler
Original assignee: Joanneum Research Forschungsgesellschaft M.B.H.
Priority date: 2007-06-14
Filing date: 2008-06-13
Publication date: 2008-12-18
Also published as: AT505337A1; AT505337B1

Abstract

Disclosed is a sensor (1), particularly an oxygen sensor for detecting gaseous or dissolved oxygen. Said sensor (1) comprises an organic light emitting diode (2), a first polarizing filter (3), an organic fluorescent or phosphorescent layer (4), a second polarizing filter (5), and at least one organic photodiode (6, 12).

Description

Sensor for the detection of gases

The invention is based on a sensor for detecting gases, in particular oxygen.

There are several types of oxygen sensors that detect the partial pressure of oxygen in different environmental conditions and in different areas (e.g., heating systems, internal combustion engines, medical technology).

By way of example, Fig. 1 shows the principle of an oxygen sensor operating by means of a zirconia probe. The ceramic material zirconium oxide is a solid electrolyte and is suitable as an oxygen ion conductor. Within a certain temperature range, which depends on the doping of the zirconium oxide, it has the ability to incorporate oxygen ions in vacancies of the crystal lattice. The oxygen ions are formed on a conductive contact layer, which is usually made of platinum. The concentration of oxygen in a sample gas is thus crucial for the level of oxygen activity or the number of oxygen ions. The basic structure of a sensor provides a solid electrolyte, which is contacted on both sides. One side of the electrolyte is filled with a reference gas, e.g. Air operated, the other side with sample gas. The mechanical design of the sensor separates both gas sides from each other, so that a mixing of the gases is prevented. Depending on the application, heated or unheated sensors are used. The oxygen partial pressure is measured by the voltage (electromotive force) tapped at the electrodes.

Furthermore, oxygen sensors are known which are based on the principle of a galvanic fuel cell for measuring the oxygen partial pressure. The ambient atmosphere or the measurement gas diffuses through a synthetic membrane to a thin electrolyte layer to the cathode of the sensor. The electrolyte, the cathode material and the composition of the anode, which consists mainly of lead, are designed so that oxygen that diffuses to the cathode is electrochemically reduced. At the same time, the anode material is oxidized. Since the cathode and anode of such sensors are electrically contacted, an ion current flows through the sensor. The corresponding electrical current corresponds to the oxygen partial pressure and can be measured in series by a resistor. The diffusion through the membrane and the thin electrolyte layer are complex temperature dependent electrochemical processes that affect the ion current of the sensor. For this reason, such a sensor must be temperature compensated, so that the sensor signal is approximately independent of temperature changes within the specified temperature range, which implies a high cost in the manufacture and operation of such a sensor.

Oxygen sensors based on optical principles are also known. In an optical measuring cell, laser light is reflected back and forth with the help of mirrors until it has traveled a total distance of about 1 meter. The laser source used is a vertical cavity surface emitting laser (VSEL). The VCSELs used emit light at a wavelength of 760 nm. At this wavelength oxygen absorbs and thus the molecule can be detected very sensitively.

Furthermore, fiber optic oxygen sensor are known. The basic principle of the fiber optic oxygen sensor is a fluorescent probe with a thin film at the tip and a blue LED as the excitation source. The sensor measures the absolute oxygen concentration via fluorescence measurement technology. Through an optical fiber, the light of the blue LED is brought to the thin film on the probe tip. The excited fluorescence is reflected back and returned to the spectrometer via optical fibers. There, to suppress the reflected excitation light, a 550nm edge filter is incorporated. If oxygen diffuses into the gas to be measured or into the liquid, then the fluorescence goes out and the degree of extinction correlates directly with the oxygen concentration.

A disadvantage of conventional optically operating oxygen sensors is mainly that the light source, the detector (s) and the optical elements are discrete, comparatively large components which are assembled and held by mechanical or adhesive bonds. This means that such sensors can reach a considerable size and their production can be carried out only to a limited cost.

Therefore, their use is in very large numbers, for example, when it comes to single-item tagging, so the monitoring of individual pieces, both production-related and especially cost-sided not feasible. The object of the invention is thus to provide an integrated sensor which is small, lightweight and inexpensive.

The object is achieved by a sensor which comprises an organic light emitting diode, a first polarizing filter, an organic fluorescent or phosphorescent layer, a second polarizing filter, and at least one organic photodiode.

The main advantage of using the polarization filter is the complete independence of the wavelength difference between excitation light and fluorescent light. The difference may also be zero nanometers. Thus, even fluorescent dyes that have only a very small Stokes shift, but good detection properties, and their emission via conventional thin-film filter can not be separated sufficiently from the excitation, are used.

Further advantageous embodiments and modifications of the invention will become apparent from the dependent claims.

In the figures, preferred embodiment of the invention are shown schematically and explained in more detail in the following description. Show it:

1 is a schematic view of an oxygen sensor according to the prior art,

2 shows a schematic overall view of a sensor arrangement for use with an organic oxygen sensor designed according to the invention,

3 shows a schematic view of the arrangement of the polarization filters of an oxygen sensor according to the invention,

4A-D highly schematic representations of the layer structure of preferred embodiments of inventive oxygen sensors,

5 is a schematic representation of an organic light emitting diode for use with an inventively designed organic oxygen sensor, 6 shows a schematic representation of an organic photodiode for use with an organic oxygen sensor designed according to the invention,

7 shows a graphic illustration of a functional verification of an oxygen sensor designed according to the invention, and FIG

8 shows a graphic illustration of the suppression of the excitation light in an oxygen sensor designed according to the invention.

A general arrangement of an inventively designed organic oxygen sensor 1 is shown schematically in Fig. 2. A sensor, in particular an oxygen sensor 1 according to the subject invention basically comprises the following elements:

an organic light-emitting diode (oLED) 2, which supplies the light for the generation of the luminescence of the organic oxygen-sensitive dye, a wavelength separator 7, and

- An organic photodiode 6, which detects the emitted luminescence of the dye.

The wavelength separator 7 comprises the following subelements:

a polarization filter 3 which linearly polarizes the light emitted by the oLED 2,

an organic fluorescent or phosphorescent layer 4, on which the lifetime of the luminescence depends on the partial pressure of oxygen to which the layer is exposed, and whose emitted luminescent light has a certain degree of depolarization, and a further polarization filter 5, the direction of which is crossed to the the first is and suppresses the linearly polarized excitation light light.

Other elements such as additional polarizers, edge filters and photodiodes can be added depending on the embodiment, for example, to increase the sensitivity of the oxygen sensor 1, to improve the signal-to-noise ratio, to adapt the oxygen sensor 1 to a certain oxygen partial pressure or litter - and to suppress ambient light. Embodiments with additional components are described in more detail below. In principle, the organic light-emitting diode 2 is excited with a sinusoidally modulated voltage whose modulation frequency is adapted to the lifetime of the luminescence, as indicated on the left in FIG. 2. Thus, a sinusoidal photocurrent or a sinusoidal photovoltage is also supplied by the organic photodiode 6, which has a phase shift φ to the excitation voltage, as shown in Fig. 2 right. The size of this phase shift φ is essentially dependent on the luminescence lifetime of the organic dye in the layer 4 and thus on the oxygen partial pressure to be determined.

The oxygen sensor 1 can be coupled with a reading device, not shown further, which also takes over the power supply for the light-emitting diode 2. The coupling of the oxygen sensor 1 to the reading device can be carried out inductively via electrical contacts or via a built-in oxygen sensor 1 high-frequency transmission part.

In Fig. 3, the operating principle of the suppression of the excitation light by a suitable arrangement of polarizers 3, 5 in the wavelength separator 7 is shown schematically.

FIGS. 4A to 4D show highly schematically preferred embodiments of organic oxygen sensors designed according to the invention. In each case, a section through the layer structure of the oxygen sensor is shown.

A first embodiment of the subject invention according to FIG. 4A consists of an organic light-emitting diode 2, a substrate 8, a first polarizer 3, a first spacer 9, an active sensor layer 4, possibly a second spacer 10, a second polarizer 5, whose self-direction 90 ° with that of the first includes, and an organic photodiode 6, which detects the luminescence emitted by the active sensor layer 4 luminescent light.

A second embodiment of the subject invention according to FIG. 4B consists of an organic light-emitting diode 2, a substrate 8, a first polarizer 3, a first spacer 9, an active sensor layer 4, a second spacer 10, an edge filter 11 for suppressing the excitation light second polarizer 5, whose self-direction includes 90 ° with that of the first, and an organic photodiode 6, which detects the luminescence emitted from the active layer 4 luminescent light. A third embodiment of the subject invention according to FIG. 4C consists of an organic light emitting diode 2, a substrate 8, a first polarizer 3, a first spacer 9, an active sensor layer 4, possibly a second spacer 10, a first organic photodiode 12 for detecting the Excitation light with a certain transparency for the emitted luminescent light, a second polarizer 5, whose self-direction includes 90 ° with that of the first, and a second organic photodiode 6, which detects the luminescence emitted from the active layer 4 luminescence.

A fourth embodiment of the subject invention according to FIG. 4D consists of an organic light-emitting diode 2, a substrate 8, a first polarizer 3, a first spacer 9, an active sensor layer 4, possibly a second spacer 10, a first organic photodiode 12 for detecting the Excitation light with a certain transparency for the emitted luminescent light, an edge filter 11 for suppressing the excitation light, a second polarizer 5 whose self-direction includes 90 ° with that of the first, and a second organic photodiode 6, which detects the luminescence emitted from the active layer luminescence.

The spacer (s) 9, 10 according to FIGS. 4A to 4D can cover all or part of the surface of the substrate 8. If the lateral possibility for lateral diffusion is sufficient, the spacers 9, 10 can also be dispensed with.

In any embodiment of the invention, each of the layers described may completely or partially cover the cross-section.

In each embodiment, the invention contains as light source an organic light-emitting diode 2, which is shown by way of example in FIG. The organic light-emitting diode 2 is manufactured in sandwich structure. One or more organic thin films are contacted by two electrically conductive electrodes 13, 14. The organic light emitting diode 2 typically consists of a hole and an electron transport layer (HTL and ETL). At the cathode 13, electrons are injected at the anode 14 holes.

As materials for an oLED 1, which emits at 530 nm (green light), for the ETL aluminum tris (8-hydroxyquinoline) and the HTL N, N ^Λ -bis (1-naphthyl) -N ₅ N "-diphenyl-l , r-biphenyl-4,4 ^Λ diamine, used for the cathode 13 aluminum and for the anode 14 indium tin oxide. For an oLED 2 emitting between 400 and 425 nm (blue light), para-hexaphenyl can be used as the emitter material and N, N-diphenyl-N, N '- (3-methylphenyl) -1,1'-biphenyl-4 as a hole transport layer , 4'-diamines are used.

In each Ausfohrungsform the invention contains an organic luminescent layer 4, which is applied by suitable methods (eg spin coating, dip coating, knife coating, curtain coating or vapor deposition) and the luminescence lifetime is a sufficiently strong function of the oxygen partial pressure, the Layer 4 is exposed for detection.

In each embodiment, the invention includes at least one organic photodiode 6, 12 for detecting the emitted fluorescent light or the excitation light, which is shown schematically in Fig. 6. The organic photodiode 6, 12 is manufactured in sandwich structure. One or more organic thin films are contacted by two electrically conductive electrodes 15, 16. The starting point for the fabrication of the photodiode 6, 12 is, for example, a glass substrate 17. For structuring the individual components of the photodiode various structuring methods, such as photolithography, electron beam lithography, FIB (focused ion beam) or lift-off technique can be used. The application of the organic and metallic thin films 18 takes place e.g. by vacuum sublimation in corresponding evaporator systems or by spincoats or inkjet printers of polymer materials.

FIG. 6 shows a possible embodiment which contains silver or gold as electrode materials and as organic thin films 18 the semiconductors 3,4,9,10-perylenetetracarboxylic bis-benzimidazoles and copper phthalocyanine. The maximum of the spectral sensitivity of this cell is about 615 nm. Other possible active materials are as p-type semiconductors: ZnPc, CuPc, pentacene, PTCDA, TPD and as n-type semiconductors: perylene derivatives (PTCBI, MPP), FCuPc. The organic semiconductors are chosen so that the maximum of the photocurrent sensitivity coincides with the maximum of the intensity of the light to be detected.

In each embodiment, the invention includes one or more polarizers 3, 5, embodied either as film polarizers to which the adjacent elements are suitably connected (eg by lamination or gluing with optical glue), or to the neighboring elements as Dünnschichtpolarisatoren be applied, using any technique that ensures both the desired polarization properties and the elements to which the polarizers 3, 5 are applied, not damaged, can be used. In any embodiment, the invention may include one or more spacers 9, 10 unless lateral diffusion into the organic luminescent layer is sufficient. The spacers 9, 10 are designed or structured in such a way that they allow the oxygen to enter and exit the organic luminescence layer without impairing the optical function of the oxygen sensor 1.

FIG. 7 shows the functional principle of the oxygen sensor 1 designed according to the invention: At time t = 0 sec, the active sensor layer 4 is in air, resulting in a phase difference φ between the excitation voltage of the organic light emitting diode 2 and the photovoltage of approx. 102 °. Then, the sensor layer 4 is purged with nitrogen and assumes a value of about 109 °. Then it is purged with oxygen, whereby the value goes down to about 101 °, then again with air (φ = 102 °), nitrogen (φ = 109 °), oxygen (φ = 101 °), air (φ = 102 ° ) etc.

Tab. 1 shows the exact values for the voltage at the organic photodiode 6 (oPD) and the phase shift between the excitation voltage of the organic light-emitting diode (SD) 2 and the photovoltage:

8 shows the mode of operation of the suppression of the excitation light by the use of the crossed polarizers 3, 5 and the measurement of the emitted fluorescent light in a spectrally resolved representation. The light source used was an organic light-emitting diode 2 with a maximum of the emission wavelength at 400 nm. The maximum lower two curves reflect the emission in air, the maximum upper curves when flushing the sensor layer 4 with carbon dioxide.

Claims

claims:

1. sensor (1), in particular oxygen sensor for the detection of gaseous or dissolved oxygen, comprising: an organic light emitting diode (2), - a first polarizing filter (3), an organic fluorescent or phosphorescent layer (4), a second polarizing filter (5), and at least one organic photodiode (6, 12).

2. Sensor according to claim 1, characterized in that the luminescence lifetime of the fluorescent or phosphorescent layer (4) is dependent on the oxygen partial pressure to which the layer (4) is exposed.

3. Sensor according to claim 1 or 2, characterized in that the of the fluorescent or phosphorescent layer (4) emitted light is depolarized.

4. Sensor according to one of claims 1 to 3, characterized in that the self-direction of the second polarizing filter (5) is aligned perpendicular to the direction of the first polarizing filter (3).

5. Sensor according to one of claims 1 to 4, characterized in that the polarization filter (3, 5) in the organic light emitting diode (2) and / or in the at least one organic photodiode (6, 12) are integrated.

6. Sensor according to one of claims 1 to 4, characterized in that the at least one organic photodiode (6, 12) is carried out polarizing.

7. Sensor according to one of claims 1 to 6, characterized in that a layer carrying the substrate (8) at any point of the sensor (1).

8. Device according to one of claims 1 to 7, characterized in that the layers carrying substrate (8) is flexible or rigid.

9. Sensor according to one of claims 1 to 8, characterized in that between the active layer (4) and the second polarizer (5) an edge filter (11) is arranged.

10. Sensor according to one of claims 1 to 9, characterized in that after the sensor layer (4) a first photodiode (12) is arranged; according to which the second polarization filter (5) is formed, on which a second organic photodiode (6) is arranged following.

11. Sensor according to claim 10, characterized in that between the first organic photodiode (12) and the second organic photodiode (6) an edge filter (11) is arranged.