JP4418731B2 - Photoluminescence quantum yield measurement method and apparatus used therefor - Google Patents

Description

  The present invention relates to photoluminescence (hereinafter referred to as PL) of organic and inorganic electroluminescence (EL) materials, semiconductor materials such as light emitting diodes (LED), and phosphor materials such as CRT, FED and PDP, which are used in lighting and display devices. The present invention relates to a method for measuring quantum yield and an apparatus used therefor.

The PL quantum yield of a light-emitting material is an extremely important parameter as a measure for knowing the limit of quantum efficiency when an element is formed (EL quantum efficiency in the case of electroluminescence (electroluminescence, hereinafter referred to as EL) material). It is also very important for obtaining basic knowledge of mechanisms and guidelines for optimizing light emitting materials and device structures. In addition, when calling it quantum efficiency in this-application specification, it shall use by the meaning which multiplied the extraction efficiency by the quantum yield (generally also called external quantum efficiency).
Further, the PL quantum yield of the light emitting material is defined as follows in the present specification.

  In particular, a thermal radiation detector such as a thermocouple is usually used to quantitatively measure the number of emitted photons that are molecules of the above formula, but the response of the thermal radiation detector is poor and sensitivity is also high. Since it is low, there was a problem that sufficient measurement accuracy could not be obtained.

For this purpose, a technique that can accurately measure the PL quantum yield of a light-emitting material using an integrating sphere and a high-sensitivity spectrometer has been known (see Patent Document 1).
Since this method can make the light emission uniform by multiple diffuse reflection inside the integrating sphere, there is an advantage that there is no need to consider the light distribution and the measurement time can be shortened. Furthermore, by accurately measuring the spectral sensitivity of the entire apparatus including the integrating sphere, an accurate PL quantum yield can be obtained.
This method is effective to some extent for a phosphor material having a relatively large film thickness such as PDP.

  However, in an organic or inorganic EL thin film material having a very small thickness, not only the reflected light from the sample due to the excitation light irradiation but also the transmitted light cannot be ignored. Furthermore, since the guided wave in the transparent substrate for light emission cannot be ignored, it is necessary to arrange the measurement sample inside the integrating sphere.

A problem that occurs when using an integrating sphere is re-excitation emission from the sample. When the measurement sample placed inside the integrating sphere is irradiated, the sample is not only emitted by direct irradiation of the excitation light, but also diffused and reflected by the sample surface, and then again by the excitation light re-reflected by the inner wall of the integrating sphere. Is light emission generated by excitation. The same applies to the transmitted light. Therefore, the measured total amount of light emission includes such re-excitation light emission.
In order to remove the influence of this re-excitation luminescence, an experimental method as shown in FIG. 2 is known (see Non-Patent Document 1).

  That is, in this experimental method, first, as shown in FIG. 2A, excitation light (laser light) 101 is made incident into the integrating sphere 105 without inserting the sample into the integrating sphere 105, and the optical spectrum is obtained. Measurement is performed by the photodetector 108. Note that a baffle 107 is provided immediately before the photodetector 108 in order to prevent direct incidence of light emitted from the sample 103. Next, as shown in FIG. 2B, in order to measure the influence of the re-excitation light emission, the light spectrum is measured with the sample 103 disposed at a position in the integrating sphere 105 where the excitation light 101 does not directly hit. Measurement is performed by the detector 108. Next, as shown in FIG. 2C, the sample 103 is disposed on the irradiation light path of the excitation light, and the optical spectrum when the excitation light is irradiated on the sample 103 is measured by the photodetector 108. Finally, the PL quantum yield is calculated from the measurement results of these three optical spectra.

JP-A-9-292281 “AnImproved Experimental Determination of External Photoluminescence QuantumEfficiency”, J. C. de Mello, H F. Wittmann, R H. Friend, Adv. Mater. 9,230 (1997)

Although the method described in Non-Patent Document 1 can remove the influence of re-excitation light emission in principle, it requires a measurement time and has a problem in measurement accuracy because it requires a technical measurement procedure.
Furthermore, ultraviolet light is often used because the excitation light requires a high energy output, but in the ultraviolet wavelength region, the wavelength dependence of the spectral reflectance of BaSO ₄ applied to the inner wall of the integrating sphere As a result, the integration efficiency of the integrating sphere decreases. For this reason, a spectral irradiance standard bulb with a spectral distribution is used, and the light from the standard irradiance standard bulb is made incident on the integrating sphere under the same imaging conditions as the excitation light. It is common to calibrate the device.

  However, depending on the spectral transmittance and chromatic aberration of the lens, the spectral reflectance of the mirror and diffraction grating, and the wavelength dependence of the sensitivity of the photodetector, the relative spectral power distribution of the standard irradiance light bulb is distorted. A large error occurs in the calibration of the laser beam, and there is a problem that the absolute optical spectrum cannot be measured accurately. As a result, the obtained PL quantum yield value includes a large error.

  As described above, the conventional PL quantum yield measurement methods for light-emitting materials are all based on assumptions that cause uncertainty, or are based on calibration methods that include uncertainty. The rate was unreliable. Measurements must also be as simple as possible to reduce uncertainty.

  The present invention has been made in view of the above circumstances, and is a calibration method that shortens measurement time and improves measurement accuracy by using an integrating sphere, and eliminates uncertain assumptions in the absolute sensitivity calibration of the entire measurement apparatus. It is an object of the present invention to provide a PL quantum yield measuring method and apparatus for a luminescent material that is simpler and more accurate.

The PL quantum yield measurement method according to the present invention includes:
A sample made of a luminescent material is arranged in the integrating sphere, the sample is irradiated with excitation light, and the spectrum intensity of the light emitted from the sample is measured using the emission spectrum detecting means attached to the integrating sphere. A photoluminescence quantum yield measurement method characterized by obtaining a photoluminescence quantum yield by:
The intensity of the reflected light reflected from the sample in response to the irradiation of the excitation light and the intensity of the transmitted light transmitted through the sample are each measured by a light detection means separate from the emission spectrum detection means, and the intensity of the excitation light And the PL quantum yield is obtained based on these measurement results.

  Moreover, it is preferable to obtain | require PL quantum yield by calculating each said measurement result using the following Formula (A).

  Further, it is preferable to determine the PL quantum yield by measuring the scattered light intensity from the sample placed in the integrating sphere, taking this measurement result into account, and calculating using the following conditional expression (B). .

  Moreover, it is preferable to capture the reflected light and transmitted light of the excitation light in the sample without irradiating the inner surface of the integrating sphere.

  Furthermore, it is preferable that the measurement part including the integrating sphere is arranged in a dry nitrogen atmosphere.

Moreover, the PL quantum yield measuring apparatus according to the present invention is:
In an apparatus for measuring the PL quantum yield of a luminescent material,
An integrating sphere in which a sample made of a luminescent material is disposed;
An excitation light source disposed outside the integrating sphere and irradiating the sample with excitation light;
A first photodetector for detecting a spectral intensity of light emitted from the sample in response to irradiation of the excitation light;
Second and third photodetectors for detecting reflected light reflected from the sample in response to irradiation of the excitation light and transmitted light transmitted through the sample, respectively;
Measurement results detected by the first, second and third photodetectors;
Based on the measurement result relating to the intensity of the excitation light, a calculation means for calculating the PL quantum yield of the sample;
It is characterized by having.

  Further, at least two light exit holes are provided at predetermined positions of the integrating sphere, and the second and third photodetectors are configured so that reflected light and transmitted light of the excitation light on the sample are integrated on the inner surface of the integrating sphere. It is preferable that the light emitting hole is disposed outside the light emitting hole so that the light can be captured without being irradiated.

  The second and third photodetectors and the detector for obtaining a measurement result relating to the intensity of the excitation light are optical power meters, and the first photodetector is a photodiode, a photomultiplier tube, and a CCD multi-sensor. It is preferably one of the channel detectors.

Here, the “detector that obtains the measurement result relating to the intensity of the excitation light” is not prevented from being the same detector as the second or third photodetector.

  Further, the PL measuring unit including the integrating sphere, the detector for obtaining the measurement result relating to the intensity of the excitation light, and the first, second and third photodetectors is installed in a glove box filled with dry nitrogen. It is preferable.

  Further, a sample preparation unit for preparing the sample is connected to the integrating sphere, a detector for obtaining a measurement result relating to the intensity of the excitation light, and a PL measurement unit including the first, second and third photodetectors. In addition, it is preferable that the sample is transported to the PL measurement unit without being exposed to the atmosphere after being prepared.

According to the PL quantum yield measuring method of the present invention and the apparatus used therefor, it is possible to obtain a highly reliable PL quantum yield for a light emitting material to be measured.
That is, the excitation light used for measurement is generally laser light from a continuous oscillation type ultraviolet laser light source, and is light having a very narrow wavelength width. On the other hand, light emission often shows a spectrum with a wide wavelength width in the visible region. As described above, it is extremely difficult to measure and compare light with completely different properties with the same photodetector with high accuracy from the viewpoint of sensitivity and dynamic range.

  Therefore, according to the PL quantum yield measurement method of the present invention and the apparatus used therefor, the reflected light and transmitted light of the excitation light in the sample are measured by a photodetector separate from the detector for emission spectrum measurement. The intensity of the excitation light is measured, and the PL quantum yield is calibrated and obtained based on the measurement results, and the calibration calculation is performed based on highly accurate information regarding the excitation light that contributes to the light emission. Therefore, the PL quantum yield can be obtained easily and with high accuracy.

  In addition, this makes it possible to know the limit of the device quantum efficiency before making the light emitting material into an element, and to obtain important guidelines for optimizing the light emitting material and the element structure.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic diagram (cross-sectional view) for explaining a PL quantum yield measuring apparatus according to an embodiment of the present invention.

  The PL quantum yield measuring apparatus shown in FIG. 1 includes an integration including an excitation light incident port 1P1, a transmitted light exit port 2P2, a reflected light exit port 3P3, an emission spectrum measurement port 4P4, a baffle 7, and a measurement sample attachment 6. A sphere 5, an excitation light source (laser) 1, an emission spectrum detector 8 including a spectroscope 8 a and a CCD photodetector 8 b, and an optical power meter that detects transmitted light and reflected light from the sample 3 due to excitation light irradiation. 9a, 9b and a control computer 10 are provided.

The integrating sphere 5, the emission spectrum detector 8, and the optical power meters 9a and 9b are arranged in the glove box 4 in a dry nitrogen atmosphere.
Further, an ND filter 2 is disposed on the output side of the excitation light source 1, and a window 11 made of a transparent plate is formed at the excitation light incident position of the glove box 4.

As the excitation light source 1, for example, a light source capable of outputting an ultraviolet laser such as a He—Cd laser (wavelength 325 nm, intensity 10 mW, beam diameter 1 mm) is used. In this case, a laser having a wavelength and intensity suitable for the light emitting material to be measured is preferable. The ND filter 2 is disposed for the purpose of measuring the excitation intensity dependency and the like, and is installed using a holder (not shown) in the vicinity of the laser emission position.
In the present embodiment, the measurement sample 3 made of a thin film of an organic EL material is installed at the approximate center position of the integrating sphere 5 using the measurement sample attachment 6.

  In addition, in the atmosphere, the organic EL thin film is irradiated with ultraviolet rays, so that the photobleaching effect causes deterioration and changes in emission color ("multi-color organic EL element using a dye-dispersed polymer", Kido, Yamagata , Hara, see 44th Applied Physics Related Conference Proceedings No.3, p.1156, 29p-NK-14 (1997)), in glove box 4 filled with dry nitrogen and extremely low oxygen concentration I am trying to make measurements.

  As described above, the integrating sphere 5 (inner diameter 200 mm) is provided with the four ports P1 to P4, and the attachment 6 and the baffle 7 for fixing the measurement sample are mounted. The port 1P1 is a port for excitation light incidence. Further, when the measurement sample 3 is arranged in the integrating sphere 5, re-excitation light emission due to the reflected light from the inner wall surface of the integrating sphere becomes the most problematic, but the port 2P2 and the port 3P3 are transmitted and reflected from the sample 3 respectively. It serves as an optical trap for each of the lights, and the heads of the optical power meters 9a and 9b are attached to the positions outside the ports 2P2 and 3P3. These optical power meters 9a and 9b are for measuring the light intensity Er of reflected light and the light intensity Et of transmitted light (both units are W). Further, the port 4P4 is equipped with an emission spectrum detection unit 8 (consisting of a spectroscope 8a and a CCD photodetector 8b) for measuring light emission from the sample 3. The baffle 7 is disposed at a position where the direct incident light emitted from the measurement sample 3 can be shielded with respect to the port 4P4.

  The control computer 10 is connected to the photodetector 8b and the measuring devices of the optical power meters 9a and 9b, controls the settings of these measuring devices, and measures obtained by these measuring devices. It has a function to analyze and analyze data.

  The diameter of the integrating sphere 5 used for measurement is preferably at least 200 mm in order to reduce the influence of the port. In addition, in order to prevent the pumping light incident on the optical power meters 9a and 9b of the ports 2P2 and 3P3 from returning to the integrating sphere again, the reflected light from the optical power meters 9a and 9b is transmitted to the ports 2P2 and 3P3. The angle is adjusted so that it does not enter. The diameters of the port 2P2 and the port 3P3 are preferably 10 mm or less.

The excitation light source 1 to be used is a light source that can emit laser light having a small beam divergence angle and a small beam diameter in order to facilitate adjustment of the optical axis and to remove unnecessary scattered light and reflected light. .
Moreover, the attachment 6 for fixing a sample uses what was comprised from the very thin transparent acrylic rod and transparent quartz glass so that the influence in the case of a measurement could be made small.

  In this embodiment, an optical power meter is used as the photodetector. However, the optical power meter has a fixed wavelength for excitation light, reflected light from the sample 3, and transmitted light. This is particularly effective when measuring strength. Among these optical power meters, when measuring the light intensity (unit: W) of a short-wavelength continuous wave laser, the measurement accuracy is higher in the ultraviolet wavelength region than the optical power meter using a silicon photodiode. An optical power meter using a thermocouple with less wavelength dependency is more effective.

  On the other hand, for light emission from the sample 3, the photodetector may be a photodiode, a photomultiplier tube, or a CCD multichannel detector, but it has a wide spectral width and a measurement time. The CCD multi-channel detector is desirable from the viewpoint of shortening and simplicity, and from the viewpoint of sensitivity, the liquid nitrogen cooled or electronically cooled CCD photodetector described above is desirable.

Next, procedures for measuring and calculating the PL quantum yield will be described.
By irradiating the sample 3 in the integrating sphere 5 with the excitation light from the excitation light source 1, PL light is emitted from the sample 3, and the emission spectrum intensity L (λ) ( The unit is W / nm and λ is the wavelength), the optical power meter 9a obtains the reflected light intensity Er, and the optical power meter 9b obtains the transmitted light intensity Et.
Next, the sample 3 is removed from the integrating sphere 5, and the power Ei of the excitation light source 1 is measured by the optical power meter 9b.

  As described above, the PL quantum yield is given by the following formula (1), and the number of photons absorbed in the measurement sample 3 corresponding to the denominator of the formula (1) is expressed as follows. It is expressed as the following formula (2).

  In the case of a sample having a flat surface, it is only necessary to consider reflected light and transmitted light. However, in the case of a sample having an uneven surface, it is necessary to consider the scattered light intensity Es. 2) is expressed as the following formula (3).

したがって、ＰＬ量子収率η_ＰＬは下式（４）に基づいて求められる。

Therefore, the PL quantum yield η _PL is obtained based on the following equation (4).

  The calculation using the above equation (4) is performed in the control computer 10 based on a predetermined calculation program.

  The optical power meters 9a and 9b are generally marketed in a pre-calibrated state. However, the integrating sphere 5, the spectroscope 8a, and the CCD photodetector 8b need to be calibrated when used by each user. Spectral irradiance standard bulbs are used for absolute calibration of all optical systems. For example, a standard irradiance bulb (100 V, 500 W) manufactured by USHIO INC. Can be used as a standard standard.

However, in order to correctly perform calibration from the ultraviolet region to the blue wavelength region, it is better to use a xenon ordinary light source that has been priced or a monochromatic light source that combines a spectroscope with a xenon lamp whose absolute intensity has been measured in advance. preferable.
FIG. 3 shows a state in which a monochromatic light source unit in which the xenon lamp 13 and the spectroscope 18 are combined is used.
In this example, monochromatic light from a monochromatic light source unit is caused to enter the integrating sphere 5 using the optical fiber 12.

In addition, the measurement described above is effective immediately after sample preparation in order to increase measurement accuracy.
In order to perform measurement immediately after sample preparation, for example, a measurement system as shown in FIG. 4 may be used.
That is, as shown in FIG. 4, the sample preparation device 21 is connected to the glove box 4 which is a PL quantum yield measuring means, and the sample 3 prepared by the sample preparation device 21 is conveyed into the integrating sphere 5 without exposure to the atmosphere. Then, the PL quantum yield is measured by placing the integrating sphere 5 at a predetermined position.

  Thereby, an accurate PL quantum yield can be measured without deterioration even in a material that is easily affected by water or an oxygen material such as an organic EL material.

The PL quantum yield measuring method and apparatus of the present invention are not limited to those of the above-described embodiments, and various modifications can be made.
For example, according to the above embodiment, an organic EL material is used as a measurement sample. However, the measurement sample is not limited to this, and an inorganic EL material and a light-emitting diode (LED) semiconductor material, as well as CRT, FED, etc. The present invention can also be applied to a phosphor material such as PDP. Moreover, it is applicable not only to thin film samples but also to powder and solution samples.

Schematic showing a PL quantum yield measuring apparatus according to an embodiment of the present invention The figure for demonstrating the procedure which measures conventional PL quantum yield Schematic showing a partial modification of the PL quantum yield measuring apparatus shown in FIG. Schematic which shows the change aspect of PL quantum yield measuring apparatus shown in FIG.

Explanation of symbols

1,21 Excitation light source (laser)
2 ND filter 3, 103 Sample 4 Glove box 5, 105 Integrating sphere 6 Measurement sample attachment 7, 107 Baffle 8, 108 Emission spectrum detector 8a, 18 Spectrometer 8b CCD photodetector (photo detector)
9a, 9b Optical power meter 10 Control computer 11 Window 12 Optical fiber 13 Xenon lamp 21 Sample preparation device 23 Sample transport part P1, P2, P3, P4 port

Claims (10)

A sample made of a luminescent material is arranged in the integrating sphere, the sample is irradiated with excitation light, and the spectrum intensity of the light emitted from the sample is measured using the emission spectrum detecting means attached to the integrating sphere. A photoluminescence quantum yield measurement method characterized by obtaining a photoluminescence quantum yield by:
The intensity of the reflected light reflected from the sample in response to the irradiation of the excitation light and the intensity of the transmitted light transmitted through the sample are each measured by a light detection means separate from the emission spectrum detection means, and the intensity of the excitation light And measuring the photoluminescence quantum yield based on these measurement results. 2. The photoluminescence quantum yield measurement method according to claim 1, wherein the photoluminescence quantum yield is determined by calculating each measurement result using the following formula (A).

By measuring the scattered light intensity from the sample placed in the integrating sphere, and using the following formula (B) in consideration of the measurement result of the scattered light intensity instead of the formula (A) 3. The photoluminescence quantum yield measuring method according to claim 2, wherein a photoluminescence quantum yield is obtained.

  4. The photoluminescence quantum yield measurement method according to claim 1, wherein reflected light and transmitted light of the excitation light in the sample are captured without irradiating the inner surface of the integrating sphere. 5. .   The photoluminescence quantum yield measuring method according to any one of claims 1 to 4, wherein the measuring section including the integrating sphere is arranged in a dry nitrogen atmosphere. In an apparatus for measuring the photoluminescence quantum yield of a luminescent material,
An integrating sphere in which a sample made of a luminescent material is disposed;
An excitation light source disposed outside the integrating sphere and irradiating the sample with excitation light;
A first photodetector for detecting a spectral intensity of light emitted from the sample in response to irradiation of the excitation light;
Second and third photodetectors for detecting reflected light reflected from the sample in response to irradiation of the excitation light and transmitted light transmitted through the sample, respectively;
An arithmetic means for calculating the photoluminescence quantum yield of the sample based on the measurement results detected by the first, second and third photodetectors and the measurement result on the intensity of the excitation light;
A photoluminescence quantum yield measuring apparatus comprising:   At least two light exit holes are provided at predetermined positions of the integrating sphere, and the second and third photodetectors irradiate the inner surface of the integrating sphere with reflected light and transmitted light of the excitation light from the sample. The photoluminescence quantum yield measuring device according to claim 6, wherein the photoluminescence quantum yield measuring device is arranged at a position outside the light emitting hole so that the light emitting hole can be captured without being carried out.   The second and third photodetectors and the detector for obtaining a measurement result relating to the intensity of the excitation light are optical power meters, and the first photodetector is a photodiode, a photomultiplier tube and CCD multichannel detection. 8. The photoluminescence quantum yield measuring device according to claim 6, wherein the photoluminescence quantum yield measuring device is any one of a vessel.   A photoluminescence measuring unit including the integrating sphere, a detector for obtaining a measurement result relating to the intensity of the excitation light, and the first, second and third photodetectors is installed in a glove box filled with dry nitrogen. The photoluminescence quantum yield measuring apparatus according to any one of claims 6 to 8, wherein:   A sample preparation section for preparing the sample is connected to the integrating sphere, a detector for obtaining a measurement result relating to the intensity of the excitation light, and a photoluminescence measurement section including the first, second and third photodetectors. 10. The photoluminescence quantum collection according to claim 6, wherein the sample is transported to the photoluminescence measurement unit without being exposed to the atmosphere after being prepared. Rate measuring device.

Images