RU103921U1 - SYSTEM FOR DETERMINING THE SPECTRAL AND KINETIC CHARACTERISTICS OF LUMINESCENCE IN THE VISIBLE AND NEAR IR IR RANGE (OPTIONS) - Google Patents

Abstract

 1. A system for determining the spectral and kinetic characteristics of luminescence in the visible and near infrared ranges, including a laser, holder, fast optical system, a monochromator with astigmatism compensation, equipped with a 4-position turret for automatic change of diffraction gratings, an automated filter wheel with broadband light filters in front of the entrance slit of the monochromator, the first photomultiplier for the near infrared and the second for the visible and near-infrared, cooled by rmoelectrically, two collimating lenses between the output slots of the monochromator and two photoelectronic multipliers, a multi-channel time analyzer, two amplifiers transmit the amplified signal from the corresponding photoelectronic multiplier to a multi-channel time analyzer, and the main units are controlled by a personal computer, characterized in that the luminescence radiation is collected at high aperture optical system consisting of a lens and a spherical mirror transmitted by the lens t falls on the first turning mirror at an angle of 45 ° and then is reflected at an angle of 45 °, hitting a nearby second turning mirror, the first turning mirror and the second turning mirror are set to rotate the image of the horizontal luminous region inside the cuvette by 90 ° and project it onto vertical entrance slit of the monochromator; four diffraction gratings are installed in the 4-position turret of the monochromator; the holder is equipped with a magnetic stirrer and installed so that the cell with the sample is placed in

Description

The utility model relates to the field of technology for spectroscopy and can be used in studies with nanosecond time resolution of luminescence in the visible and near infrared spectral ranges.

The study of the kinetic signals of the acceleration and decay of luminescence is one of the main methods for studying the properties of molecules in excited states. It provides information on the ways and efficiencies of intramolecular conversion of photoexcitation energy, intermolecular processes of energy and charge transfer, structural changes and other reactions involving excited electronic states. In recent years, the task of studying the dynamics of luminescence in the near-IR spectral range has become especially urgent in connection with the advent of new drugs-sensitizers for photo-dynamic therapy, which form singlet oxygen ¹ O ₂ when illuminated, as well as with the development of biological labels based on rare-earth elements and nanoscale semiconductor particles (quantum dots).

A known system for recording the spectra and kinetics of luminescence [1], in which the excitation source is a dye laser pumped by an excimer laser. A focusing lens is placed between a standard 10 × 10 mm cuvette holder and a laser. In front of the entrance slit of the monochromator, a wide-band filter with a focusing lens is installed. The light flux allocated by the monochromator of the spectral range through the lens is fed to a photomultiplier tube (PMT) R5509 (Hamamatsu). Part of the photon flux exciting the sample is directed to the photodiode, which starts the MSA 200 multichannel time analyzer (MBA) (Becker and Hickl), which receives the amplified signal from the PMT.

In the known system for cooling the PMT, liquid nitrogen is required, which is very laborious. The temporal resolution of the MBA used is only 5 ns. To minimize light losses at the entrance slit of the monochromator, the test solution is excited through the polished bottom of the cuvette, which makes it impossible to mix the sample using standard methods and is dangerous for the eyes from the point of view of safety.

A known installation for recording the kinetics of luminescence [2]. As in system [1], the dye laser serves as the excitation source, but it is pumped by a solid-state Nd ³⁺ -YAG laser. The holder for ditches 10 × 10 mm in size is equipped with a mixer. The collection of light is perpendicular to the direction of the exciting beam. A spherical mirror is installed on the opposite side of the cell, increasing the amount of fixed light. Then, through a lens and one of several interference filters, luminescence is transmitted for registration to a PMT N10330-45 (Hamamatsu). To obtain the luminescence kinetics, an MBA is used, which is triggered through the photodiode by a part of the light flux going to excite the sample.

However, the lack of spectral resolution and the relatively small time range of the recording system (from 20 ns to 82 μs) limit the scope of this setup.

The closest in technical essence is the system described in [3]. In it, samples are excited by a solid-state diode-pumped laser. A 10 × 10 mm cuvette with the test solution is placed in the holder. A focusing lens is used to increase the power density of the exciting beam. The collection of luminescence is carried out at an angle of 90 ° to the direction of the exciting beam. Using a lens system and through a polarizer, the glow is transmitted to the entrance slit of the monochromator, in which it is successively reflected from two diffraction gratings. To cut off the background radiation of the infrared range from the excitation source, a special filter is placed between the laser and the cell. Also, in front of the entrance slit of the monochromator, a filter can be installed that does not transmit visible radiation. The monochromator has two outputs: for one PMT, sensitive in the visible, and the second - operating in the infrared range. As the latter, a PMT N9170-45 (Hamamatsu) is used. The electronic signal from the PMT is transmitted to the MBA MSA300 (Becker and Hickl) or Nanoharp250 (PicoQuant), embedded in the computer. The MBA is launched synchronously with the excitation pulse.

In the known setup, the response function of the registration system is 7 ns, which is not enough to study the fluorescence fluorescence, the duration of which can be several nanoseconds. In the study of biological objects, in particular, cell suspensions, their mixing is necessary to avoid photo-destruction, however, the system does not realize the ability to mix samples.

The setups [1-3] use the photon counting method, the main advantage of which is the increase in accuracy with increasing signal accumulation time. In the infrared region, the signals are often very weak, which requires significant time for measurement, during which both the intensity of the excitation source can change, and the sample under investigation can be destroyed or undergo a chemical transformation. Therefore, the use of components that track possible changes is seen as obvious, which is not done in any of the mentioned systems.

The technical problem is to increase the reliability in the characterization of substances by increasing the sensitivity and speed of known registration schemes and expanding their functionality and information content.

A system for determining the spectral and kinetic characteristics of luminescence in the visible and near infrared ranges, including a laser, holder, fast optical system, a monochromator with astigmatism compensation, equipped with a 4-position turret for automatic change of diffraction gratings, an automated filter wheel with wide-band filters in front of the input monochromator slit, the first photomultiplier for the near infrared and the second for the visible and near-infrared, cooled moelectrically, two collimating lenses between the output slots of the monochromator and two photoelectronic multipliers, a multi-channel time analyzer, two amplifiers transmit the amplified signal from the corresponding photoelectronic multiplier to a multi-channel time analyzer, and the main units are controlled using a personal computer. The holder is equipped with a magnetic stirrer and mounted so that the sample cell is placed in the common focus of the lens and the spherical mirror. A filter wheel with neutral filters is located between the laser and the holder. The trigger photodiode is located between the laser and the filter wheel with neutral filters, the transmission photodiode is located on one straight line with the laser and the cell with the sample behind the cell. A translucent plate is located at an angle of 135 ° to the exciting beam between the cell and the laser and directs part of the radiation to the trigger photodiode. The plane of polarization of the exciting beam is deflected 35 ° from the vertical. The optical system includes a lens and a spherical mirror, which is mounted on the opposite side of the lens, the first wrapping mirror and the second wrapping mirror are installed to rotate the image of the horizontal luminous region inside the cuvette by 90 ° and project it onto the vertical entrance slit of the monochromator. Four diffraction gratings are installed in a 4-position turret of the monochromator.

The holder is placed in a heat-insulating quartz vessel of the Dewar, equipped with a thermal control system, made of metal with high thermal conductivity. The filter wheel with neutral filters contains six neutral filters with a transmission of 1 to 50% and is program-controlled. The first wrapping mirror and the second wrapping mirror are made of metal that effectively reflects light in the visible and near infrared range. For the near infrared range, two gold-plated diffraction gratings are used.

Figure 1 shows a block diagram of a system where:

1 - laser;

2 - translucent plate;

3 - trigger photodiode;

4 - a filter wheel with neutral light filters;

5 - a cell with a sample;

6 - spherical mirror;

7 - lens;

8 - the general focus of the lens 7 and the spherical mirror 6;

9 - transmission photodiode;

10 - the first turning mirror;

11 - the second turning mirror;

12 - filter wheel with broadband light filters;

13 - monochromator;

14, 17 - collimating lenses;

15, 18 - photomultiplier tubes;

16, 19 - amplifiers;

20 - multi-channel time analyzer;

21 - a personal computer.

A monochromator of the brand MS2004i (SOLAR TII) with astigmatism compensation was used, equipped with a 4-position turret for automatic change of diffraction gratings, having one entrance slit 22 and two output slots of the monochromator (positions are not indicated in Fig.). As a photomultiplier tube (PMT) 15, a photomultiplier tube of the brand N10330-45 (Hamamatsu) was used. As a photomultiplier tube (PMT) 18, a photomultiplier tube of the brand H2658P (Hamamatsu) was used. As a multi-channel time analyzer (MVA) 20, the P7888-2 (FAST) board built into the personal computer 21 was used. As an amplifier 16, an amplifier of the brand C5594-44 (Hamamatsu) was used. As an amplifier 19, an amplifier of the brand 8447 F (Hewlett-Packard) was used.

Figure 2 explains the principle of operation of the image-wrapping system of mirrors, where:

5 - a cell with a sample;

7 - lens;

8 - the general focus of the lens 7 and the spherical mirror 6;

10 - the first turning mirror;

11 - the second turning mirror;

22 - input slit of the monochromator 13.

Figure 3 shows the kinetics of phosphorescence of PtOEP in toluene at 650 nm with an excitation energy of 0.2 μJ per pulse. Time resolution - 16 ns / channel. The solid line is the theoretical curve.

Figure 4 shows the kinetics of photosensitized TMPUR luminescence of singlet oxygen ( ¹ O ₂ ) in water at an excitation energy of 3.2 μJ per pulse. Time resolution - 32 ns / channel. The average noise level equal to 1500 samples is subtracted from the signal. The solid line is a theoretical two-exponential curve with time constants of 1.8 μs (the formation time of ¹ O ₂ corresponds to the lifetime of the triplet state of TMPUR) and 3.6 μs (lifetime of ¹ O ₂ in water).

Figure 5 shows the luminescence kinetics of porous silicon nanocrystals: (1) when recording at a wavelength of 1230 nm, (2) 1270 nm. To obtain each, 3 × 10 ⁴ laser pulses with energies of 3.2 μJ were used. Time resolution - 1 μs / channel.

Figure 6 shows the luminescence spectra of porous silicon obtained by integrating the kinetic signal in the range of 50-1000 μs. The excitation energy is 3.2 μJ per pulse. 3 × 10 ⁴ laser pulses per point.

The work is based on the method of counting single photons. The scheme is applied (Fig. 1), in which, after receiving the start signal from the start photodiode 3 MVA 20, the moments of arrival of all single-electron pulses generated by the PMT 15 or PMT 18 are recorded. The time resolution of the MVA 20 is 1 ns.

The samples are excited (not shown in the figure) by laser pulses (laser 1 STA-01SH, STANDA) with an energy of 4 μJ and a duration of 0.7 ns, following with a frequency of 1 kHz at a wavelength of 531 nm through a translucent plate 2, which directs part of the radiation to the trigger photodiode 3. Laser 1 is linearly polarized, and the plane of polarization is deflected 35 ° from the vertical to exclude the possible effect of anisotropy on the kinetics of luminescence decay. Excitation pulses can be attenuated by a software-controlled filter wheel with neutral filters 4, containing six neutral filters with a transmission of 1 to 50%.

The start-up photodiode 3 and transmission photodiode 9 measure the intensity of the laser pulses, respectively, before and after the cell with sample 5, which makes it possible to control during the measurement process both the stability of laser radiation 1 and the possible photodestruction of the sample.

To work with standard spectrofluorometric cuvettes 10 × 10 mm in size, a holder is used (the position is not indicated in the FIG.) Equipped with a magnetic stirrer. A magnetic stirrer provides mixing solutions of unstable samples, which otherwise may be subject to photodestruction. This is especially important for cell suspensions in order to also further ensure their uniform distribution throughout the volume of the sample cell 5.

In the second embodiment, a holder is used (the position is not indicated in the FIG.), Which maintains the temperature of the cell with sample 5 in the range from -100 ° С to + 100 ° С, which is made of metal with high thermal conductivity, placed in a heat-insulating quartz vessel of the Dewar, and equipped with a system thermoregulation. The holder is cooled by passing nitrogen gas with a temperature of about 77 K through the channels in its casing, and heated by the built-in electric heater (the position is not indicated in Fig.). An electronic controller (the position is not indicated in the FIG.), Based on the readings of a platinum resistance thermometer placed near the cell with sample 5 (the position is not indicated in the FIG.), Changes the amount of current passing through the electric heater, thereby maintaining the temperature in the holder at a constant level, set by user. Low-temperature gaseous nitrogen supplied to a thermostatically controlled holder through a heat-insulated pipe (not shown in the figure) is formed as a result of boiling liquid nitrogen in an airtight vessel. The boiling intensity is regulated by an electric heater immersed in nitrogen.

Luminescence radiation is collected by a fast optical system consisting of a lens 7 and a spherical mirror 6. A holder with a magnetic stirrer or holder is mounted so that the cell with sample 5 is placed in the common focus 8 of the lens 7 and the spherical mirror 6.

The first wraparound mirror 10 and the second wraparound mirror 11, which reflect light in the entire working range, are necessary to rotate the image of the horizontal luminous region inside the cell by 90 ° and project it onto the vertical entrance slit 22 of the monochromator 11 (Fig. 2). The first wrapping mirror 10 and the second wrapping mirror 11 are made of metal that effectively reflects light in the visible and near infrared range. The light transmitted by the lens 7 falls on the first wrapping mirror 10 at an angle of 45 ° and then is reflected at an angle of 45 °, hitting the adjacent second wrapping mirror 11. It is also set so that the angle of incidence and reflection of the luminous strip is 45 °. In this case, the dihedral angle between the planes of the first 10 and second 11 of the turning mirrors is 60 °.

An automated filter wheel with broadband filters 12 prevents diffused exciting light from entering the input of the monochromator 13. For the spectral separation of near-infrared radiation, two gold-plated diffraction gratings with maximums of brightness, approximately in the middle of this range, were used. The inverse linear dispersion of one lattice allows recording a narrow spectral range of several nanometers to record luminescence spectra, the inverse linear dispersion of a second lattice allows recording a wide spectral range of several tens of nanometers for recording luminescence kinetics.

The monochromator 13 has two gold-plated diffraction gratings of 400 and 150 lines / mm with inverse linear dispersions, respectively, 12.7 and 34 nm / mm with a maximum brightness of 1200 nm. A grating of 150 lines / mm is intended for operation of the monochromator 13 in the band-pass filter mode when it is necessary to register the integral luminescence of the entire luminescence band, for example, singlet oxygen, which has a luminescence band in water with a half width of 28 nm.

After the monochromator 13, light passes through a collimating lens 14 to the input of a photomultiplier 15 with an InP / InGaAsP based photocathode, thermoelectrically cooled to -60 ° C and having a quantum efficiency of about 2% in the infrared range. The amplifier 16 amplifies the single-electron pulses coming from the PMT 15. In this configuration, the duration of the response function of the registration system is less than 3 ns.

In addition to what is described in the system, other sources of laser pulses can also be used. In particular, Ti: sapphire laser LT-2211 (LOTIS TII), pumped by the 2nd harmonic of the Nd: YAG laser LS-2134 (LOTIS TII) with a repetition frequency, is used for excitation in the wavelength ranges of 350-480 and 650-950 nm pulses of 15 Hz.

To the second output slit of the monochromator 13, an additional photomultiplier tube — PMT 18 — is connected with a collimating lens 17 and an amplifier 19 for recording phosphorescence and / or delayed fluorescence signals in the visible and adjacent near ranges of about 550 nm with brightness maxima in the middle this range. The inverse linear dispersion of one lattice allows recording a narrow spectral range of units of nanometers for recording luminescence spectra, the inverse linear dispersion of a second lattice allows recording a wide spectral range of ten to twenty nanometers for recording the luminescence kinetics. For this purpose, diffraction gratings with maximum brightnesses of 500 and 600 nm and, respectively, with inverse linear dispersions of 4 and 17 nm / mm were added to the turret of the monochromator 13.

The lens 7 and collimating lenses 14, 17 used in the system are achromatic.

The system software allows you to automatically save the time dependence of the luminescence of the sample at different wavelengths, followed by the construction of luminescence spectra by measuring the areas under kinetic curves in a given time interval. The obtained set of experimental data contains complete information on the spectral-temporal evolution of the glow, which can then be represented in the form of a three-dimensional graph.

As an example of application, figure 3 shows the kinetics of phosphorescence at 650 nm sensitizer Pt-octaethylporfin (PtOEP) in toluene after 1.2 × 10 ⁵ excitation pulses. The concentration of PtOEP was 3.5 × 10 ⁻⁵ mol / L. The duration of phosphorescence was 210 ± 11 ns and is close to the value of 222 ns obtained in [4].

Figure 4 shows the kinetics of singlet oxygen from an aqueous solution of the sensitizer 5,10,15,20-tetrakis (4-N-methylpyridyl) porphyrin (TMPUR) after 3 × 10 ⁵ excitation pulses. A kinetic signal was obtained at a TMPyR concentration of 2.2 × 10 ⁻⁵ mol / L. The duration of the emission of singlet oxygen in water was 3.6 ± 0.2 μs and is in agreement with the values given in the review [5].

The large dynamic range implemented in the single-photon counting method and the choice of an arbitrary integration time window provide a unique opportunity to detect weak oxygen emission signals against the background of intense sensitizer luminescence. This feature of the setup was used to study the photosensitizing properties of nanocrystalline porous silicon (pSi).

It is known that silicon nanocrystals, of which pSi is composed, have luminescence in the near infrared spectral range and can be singlet oxygen sensitizers [6]. Nevertheless, the kinetics of luminescence of ¹ O ₂ on the pSi surface in air at room temperature was not detected, since pSi has long-lived intense luminescence with non-exponential attenuation in the near IR range, which hides the weak emission of singlet oxygen.

For spectral measurements, we used pSi, the layers of which were prepared by electrochemical anodizing of p-type crystalline silicon wafers with a specific resistance of 10-20 Ohm × cm and substrate orientation (100) in a solution of a mixture of hydrofluoric acid and ethanol. The pSi plate was placed in a specially designed cuvette connected to a vacuum pump.

The capabilities of the setup made it possible to detect insignificant changes in the shape of the kinetics of the luminescence decay of freshly prepared pSi in the region of 1270 nm at a temperature of 20 ° C (Fig. 5). By integrating kinetic signals in the time range, where the relative changes in intensity were maximum, emission spectra were obtained in air at normal pressure and in vacuum (Fig. 6). The spectrum with a maximum at 1270 nm and a half-width of 21 nm, observed only in the air atmosphere, belongs to luminescence ¹ O ₂ sensitized by silicon nanocrystals.

Literature:

1. Molnar A., Dedic R., Svoboda A., Hala J. // J. Mol. Struct. 2007. V.834-836. P. 488-91.

2. Schlothauer J., Hackbarth S., Röder B. // Laser Phys. Lett. 2009. V.6. Number 3. P.216-221.

3. Jiménez-Banzo A., Ragàs X., Kapusta P., Nonell S. // Photochem. Photobiol. Sci. 2008. V.7. No. 9. P.1003-1010 (prototype).

4. Bansal A.K., Holzer W., Penzkofer A., Tsuboi Taiju // Chemical Physics 2006. V.330 P.118-129

5. Schweitzer C., Schmidt R // Chem. Rev. 2003. V.103. P.1685-1758.

6. Kovalev D., Fujii M. // Adv. Mater. 2005. V.17. P.2531-2544.

Claims (11)

1. A system for determining the spectral and kinetic characteristics of luminescence in the visible and near infrared ranges, including a laser, holder, fast optical system, a monochromator with astigmatism compensation, equipped with a 4-position turret for automatic change of diffraction gratings, an automated filter wheel with broadband light filters in front of the entrance slit of the monochromator, the first photomultiplier for the near infrared and the second for the visible and near-infrared, cooled by rmoelectrically, two collimating lenses between the output slots of the monochromator and two photoelectronic multipliers, a multi-channel time analyzer, two amplifiers transmit the amplified signal from the corresponding photoelectronic multiplier to a multi-channel time analyzer, and the main units are controlled by a personal computer, characterized in that the luminescence radiation is collected at high aperture optical system consisting of a lens and a spherical mirror transmitted by the lens t falls on the first turning mirror at an angle of 45 ° and then is reflected at an angle of 45 °, hitting a nearby second turning mirror, the first turning mirror and the second turning mirror are set to rotate the image of the horizontal luminous region inside the cuvette by 90 ° and project it onto vertical entrance slit of the monochromator; four diffraction gratings are installed in the 4-position turret of the monochromator; the holder is equipped with a magnetic stirrer and installed so that the cell with the sample is placed in the focus of the lens and the spherical mirror, a filter wheel with neutral filters is located between the laser and the holder, a trigger photodiode is located between the laser and the filter wheel with neutral filters, the transmission photodiode is located on one straight line with the laser and the cell with the sample behind the cell, the translucent plate is at an angle 45 ° to the exciting beam between the cuvette and the laser and directs part of the radiation to the trigger photodiode, the plane of polarization of the exciting beam is deflected 35 ° from the vertical. 2. The system according to claim 1 is characterized in that the first wrapping mirror and the second wrapping mirror have a metal coating that effectively reflects light in the visible and near infrared range. 3. The system according to claim 1 is characterized in that for the near infrared range two gold-plated diffraction gratings are used. 4. The system according to claim 1 is characterized in that the filter wheel with neutral filters contains six neutral filters with a transmission of 1 to 50%. 5. The system according to claim 1 is characterized in that the filter wheel with neutral filters is software-controlled. 6. A system for determining the spectral and kinetic characteristics of luminescence in the visible and near infrared ranges, including a laser, holder, fast optical system, a monochromator with astigmatism compensation, equipped with a 4-position turret for automatic change of diffraction gratings, an automated filter wheel with wide-band filters in front of the entrance slit of the monochromator, the first photomultiplier for the near infrared and the second for the visible and near-infrared, cooled moelectrically, two collimating lenses between the output slots of the monochromator and two photoelectronic multipliers, a multi-channel time analyzer, two amplifiers transmit the amplified signal from the corresponding photoelectronic multiplier to a multi-channel time analyzer, and the main units are controlled by a personal computer, characterized in that the luminescence radiation is collected at high aperture optical system consisting of a lens and a spherical mirror, light transmitted by the lens falls onto the first turning mirror at an angle of 45 ° and then is reflected at an angle of 45 °, hitting a nearby second turning mirror, the first turning mirror and the second turning mirror are set to rotate the image of the horizontal luminous region inside the cuvette by 90 ° and project it onto the vertical the entrance slit of the monochromator, four diffraction gratings are installed in the 4-position turret of the monochromator, the holder is placed in a transparent quartz Dewar vessel, equipped with a thermal control system and so that the sample cuvette is placed in the common focus of the lens and the spherical mirror, the filter wheel with neutral filters is located between the laser and the holder, the trigger photodiode is located between the laser and the filter wheel with neutral filters, the transmission photodiode is located on a straight line with the laser and the cuvette with sample behind the cuvette, a translucent plate is located at an angle of 45 ° to the exciting beam between the cuvette and the laser and directs part of the radiation to the trigger photodiode, I excite the plane of polarization its beam deflected through 35 ° from the vertical. 7. The system according to claim 6 is characterized in that the first wrapping mirror and the second wrapping mirror have a metal coating that effectively reflects light in the visible and near infrared range. 8. The system according to claim 6 is characterized in that for the near infrared range two gold-plated diffraction gratings are used. 9. The system according to claim 6 is characterized in that the filter wheel with neutral filters contains six neutral filters with a transmission of from 1 to 50%. 10. The system according to claim 6 is characterized in that the filter wheel with neutral filters is software-controlled. 11. The system according to claim 6 is characterized in that the holder is made of metal with high thermal conductivity.