RU2802301C1 - Photoactive luminescent material - Google Patents

Abstract

FIELD: optical materials science.

SUBSTANCE: invention can be used in optical instrumentation as a material for photogeneration of reactive oxygen and luminescent down converters of UV radiation. The photoactive luminescent material comprises ZnO nanocrystals with a size of 8-25 nm, whereas the components are taken in the following ratio, wt.%: ZnO 62.87-82.67; ZnAl₂O₄ 17.03-36.77; CuO 0.35-0.38. This material is capable of generating reactive oxygen species, absorbing UV radiation in the wavelength range of 200-300 nm and re-emission of light in the near UV (300-380 nm) and visible spectral ranges.

EFFECT: high photocatalytic properties.

1 cl, 1 tbl, 5 dwg, 1 ex

Description

The invention relates to optical materials science and can be used in optical instrumentation as a material for photogeneration of reactive oxygen and luminescent down converters of UV radiation.

Known "Material for the conversion of vacuum ultraviolet radiation into visible radiation in the form of an amorphous film of silicon oxide SiO ₂ S _x on a silicon substrate" (RF Patent 2584205, IPC C09K 11/59, C09K 11/56, C23C 14/48, , B82B 3 /00, priority date 06/10/2014, published 05/20/2016). This patent describes a material for converting vacuum ultraviolet radiation into visible radiation in the form of an amorphous film of silicon oxide SiOS characterized in that the thickness of the amorphous film of silicon oxide SiOS is 20-70 nm, and oxygen ions are contained in an amount at which the stoichiometric coefficient "x » is in the range from 0.01 to 0.45. A significant drawback of the material described in this patent is the lack of its ability to photogenerate reactive oxygen, which determines the rapid contamination of its surface and a decrease in the efficiency of luminescent down-conversion of radiation.

A luminescent radiation converter is known, described in (Lin H., Chen D., Yu Y., Zhang R., Wang Y., Molecular-like Ag clusters sensitized near-infrared down-conversion luminescence in oxyfluoride glasses for broadband spectral modification. Applied Physics Letters. 2013. V.103. 091902) is a fluorosilicate glass containing rare earth ions (Yb ³⁺ , Tb ³⁺ ) and silver molecular clusters. The converter described in this paper is capable of efficiently converting UV radiation into light in the visible and near infrared spectral ranges. In (Enrichi F., Cattaruzza E., Finotto T., Riello P., Righini GC, Trave E., Vomiero A., Ag-sensitized NIR-emitting Yb ³⁺ -doped glass ceramics. Applied Sciences. 2020.V .10.2184.) a luminescent radiation converter is proposed that converts UV radiation into radiation in the near infrared region. This converter is a glass-ceramic material containing silver and Yb ³⁺ ions. The disadvantage of this material is the lack of bactericidal properties, which leads to contamination of its surface and a decrease in the efficiency of luminescent down-conversion of radiation.

The photoactive cell described in (RF Patent 2747332, IPC C02F 1/32, C02F 9/12, priority date 14.05.2020, published 04.05.2021) has a high ability to photogenerate reactive oxygen. A cuvette is described, inside of which a photoactive layer is located, consisting of nanoparticles of zinc and magnesium oxides and silver additives in the following at the following ratio of components, wt.%: ZnO 79.5-99; MgO 0.9-20; Ag 0.01-1.00, which provides highly efficient photogeneration of reactive singlet oxygen. The photoactive cuvette described in this patent can be effectively used for air purification and disinfection. However, the luminescence of the material of the photoactive layer containing zinc oxide and located in the cell is observed in the orange and red parts of the spectrum (in the wavelength range of 580–610 nm) and this material is not effective for use as a down converter of UV radiation.

The closest technical solution is the luminescent composite of the CuO-ZnO-ZnAl ₂ O ₄ system described in (Md Abdus Subhan, Tanzir Ahmed, Robeul Awal, Ryuzi Makioka, Hiroyasu Nakata, Tuula T. Pakkanen, Mika Suvanto, B. Moon Kim, Synthesis , structure, luminescence and photophysical properties of nano CuO∙ZnO∙ZnAl ₂ O ₄ multi metal oxide. Journal of Luminescence, 2014. V.146. P.123-127), adopted as a prototype. The composite was obtained by precipitation of metal hydroxides from solutions, followed by drying and heat treatment for 10 hours at 900°C. The luminescent material consists of oxide nanoparticles with a size of 14.8-50.0 nm, and has the ability to absorb UV radiation and re-emit light in the visible spectral range (410-500 nm). However, the ability to photogenerate reactive oxygen composite described in the prototype is not reported. In the process of heat treatment of powders, the processes of coarsening and sintering of particles actively proceed, which determines a significant decrease in the specific surface of the material. It is well known that the ability of reactive singlet oxygen to photogenerate significantly decreases with decreasing material dispersion. Considering the relatively high (900°C) heat treatment temperature of the prototype composite, it can be assumed that the ability of this material to photogenerate reactive oxygen is absent or insignificant. In addition, the prototype composite contains a large amount of copper oxide CuO (33 mol.%), which, according to (Md Abdus Subhan, Tanzir Ahmed, Robeul Awal, Ryuzi Makioka, Hiroyasu Nakata, Tuula T. Pakkanen, Mika Suvanto, B. Moon Kim, Synthesis, structure, luminescence and photophysical properties of nano CuO⋅ZnO⋅ZnAl ₂ O ₄ multi metal oxide. Journal of Luminescence, 2014. V.146. P.123-127), a separate crystalline phase. Given that copper compounds often undergo difficult to control and significant structural changes during heat treatment, the introduction of such a large amount of copper oxide into the composition of the composite can determine the instability of the properties and structure of such a material.

The objective of the present invention is to create a photoactive luminescent material for down-converters of UV radiation, with the ability to photogenerate reactive singlet oxygen.

The technical result of the invention is the creation of a material with photocatalytic and luminescent properties that can absorb UV radiation in the wavelength range of 200-300 nm and re-emit light in the near UV (300-380 nm) and visible spectral ranges.

The essence lies in the fact that the photoactive luminescent material includes ZnO, ZnAl ₂ O ₄ and CuO, characterized in that it contains ZnO nanocrystals with a size of 8-25 nm, while the components are in the following ratio, wt.%:

ZnO 62.87-82.62 ZnAl ₂ O ₄ 17.03-36.77 CuO 0.35-0.38

The proposed material is a Cu-containing ZnO/ZnAl ₂ O ₄ nanocomposite consisting of hexagonal ZnO nanocrystals and cubic crystals of ZnAl ₂ O ₄ spinel, in the structure of which Cu ²⁺ ions are embedded. ZnO nanocrystals (up to 50 nm in size) are the main component of the nanocomposite and ensure the ability of the material to photogenerate reactive oxygen. Cubic crystals of spinel ZnAl ₂ O ₄ provide conversion of UV-C radiation into UV-A and visible radiation. The content of this component in the material is 17.03-36.77 wt.%. The introduction of copper ions into the structure of the material increases the ability of the material to photogenerate reactive oxygen, which improves its photocatalytic and bactericidal characteristics. The content of copper (in terms of copper oxide CuO) is 0.35 - 0.38 wt.%. When the CuO content is less than 0.35 wt.%, the material's ability to photogenerate reactive oxygen is low. When the CuO content in the material exceeds 0.38 wt.%, a part of copper crystallizes in its structure in the form of semiconductor CuO crystals, which have a small band gap and strongly absorb radiation in the near UV and visible spectral ranges.

The photoactive material has the ability to absorb UV radiation in the wavelength range of 200-300 nm and re-emit light in the near UV (300-380 nm) and visible spectral ranges. In this case, the material has the ability to generate reactive oxygen species under the action of external radiation.

The essence of the invention is illustrated by the figures, which show:

in fig. 1 - Scheme illustrating the processes that occur when exposed to hard UV radiation on a photoactive material deposited as a coating on a transparent substrate;

in fig. 2 - X-ray pattern of the photoactive material;

in fig. 3 - Spectra of photoluminescence and excitation of luminescence of a photoactive material in the UV and visible spectral ranges;

in fig. 4 - Photoluminescence spectra of the material in the near infrared region of the spectrum when excited by radiation in the near UV range.

in fig. 5 - Photoluminescence spectra of the material in the near infrared region of the spectrum when excited by blue light radiation.

In FIG. 1 shows an exemplary scheme for using a photoactive material as a coating on a transparent substrate. When exposed to external vacuum UV or UV-C radiation, the photoactive material converts it into UV-A and visible spectral radiation. In addition, when exposed to UV radiation and blue light, reactive oxygen is formed on the surface of the material. The experiments performed have shown the high efficiency of photogeneration of reactive singlet oxygen by the proposed photoactive material and its conversion of vacuum UV and UV-C radiation into UV-A and visible spectral ranges.

The effectiveness of the developed photoactive material is illustrated by an example.

Example 1

For the synthesis of materials, polymer-salt synthesis was used, which is described in detail in the works (Dukelsky K.V., Evstropiev S.K. Formation of protective nanoscale coatings based on Al2O3 (Al2O3-AlF3) on the glass surface. - Optical journal, 2011, vol. 78, No. 2, pp. 71-81 Shelemanov A.A., Nuryev R.K., Evstropiev S.K., Nikonorov N.V., Kiselev V.M. Effect of polyvinylpyrrolidone on the structure and optical properties of ZnO-MgO 129, No. 9, pp. 1176-1181) Aqueous solutions of zinc and aluminum nitrates, as well as copper sulfate, are used as initial components for the synthesis of photoactive materials. The solutions are mixed with a solution of polyvinylpyrrolidone in propanol-2. The resulting mixtures are dried in an oven at a temperature of 70°C. The dried composites are heat treated in an electric oven at 680°C for 2 hours. This mode of heat treatment ensures complete decomposition of metal salts and polyvinylpyrrolidone. The chemical composition of the obtained composites is given in table. 1.

Table 1. Chemical composition of composites, appearance and comparative properties of materials No-measures sample Chemical composition of the material, wt.% Average size of ZnO crystals, nm Material Appearance Ability to photogenerate reactive singlet oxygen Ability to convert UV-C radiation into UV-A and visible spectral range ZnO ZnAl ₂ O ₄ CuO* 1 77.29 21.97 0.74 - Homogeneous dispersed powder Medium Medium 2 62.87 36.77 0.36 25.1 Homogeneous dispersed powder High High 3 73.22 26.42 0.36 14.1 Homogeneous dispersed powder High High 4 78.95 20.67 0.38 8.2 Homogeneous dispersed powder High High 5 82.62 17.03 0.35 14.6 Homogeneous dispersed powder High High 6 94.61 5.00 0.39 - Homogeneous dispersed powder Medium Medium 7 62.99 36.00 1.01 - Inhomogeneous material with black inclusions - - 8 90.05 - 0.95 - Homogeneous dispersed powder High Low 9 80.00 20.00 - - Homogeneous dispersed powder Medium Low 10 62.40 37.00 0.60 - Homogeneous dispersed gray powder High Medium eleven 62.89 37.01 0.10 - Homogeneous powder Medium High 12 83.00 16.85 0.15 - Homogeneous dispersed powder High Low

* In calculations, the entire content of Cu was taken in the form of CuO.

Measurements of the photoluminescence and luminescence excitation spectra in the UV and visible spectral ranges were performed on a Perkin Elmer LS-50B spectrofluorimeter. Under the action of external radiation, singlet oxygen released by the photoactive material exhibits characteristic luminescence in the near-IR region of the spectrum (λ _max =1270 nm). To excite luminescence, LEDs of the HPR40E-50UV series (λ _max =370 nm; power density 0.35 W/cm ² ) and (λ _max =405 nm; power density 0.90 W/cm ² ) are used.

In FIG. Figure 2 shows the X-ray diffraction pattern of composite photoactive composite 3 (Table 1). Peaks characteristic of hexagonal ZnO crystals and cubic crystals of spinel ZnAl ₂ O ₄ are clearly visible on the X-ray diffraction pattern. The intensity of the ZnO peaks is significantly higher than that of the spinel peaks, which is associated with a higher ZnO concentration in the composite (Table 1). Based on the analysis data using the Scherrer formula, the average size of zinc oxide crystals in composites was calculated. The results of the calculation are given in table. 1. From the data in Table. 1 shows that the size of zinc oxide crystals in composites 2÷5 is 8÷25 nm. Such small crystals have a high specific surface area, which contributes to the achievement of high photocatalytic and bactericidal properties by composite materials.

In FIG. Figure 3 shows the photoluminescence spectra (curves 1–3) and luminescence excitation (curve 4) of composite 1. Similar spectra were obtained for composites 2÷5 and 9.

In FIG. Figures 4 and 5 show the photoluminescence spectra of Cu-containing ZnO/ZnAl ₂ O ₄ composites in the near IR region of the spectrum. All spectra show a luminescence band characteristic of singlet oxygen with a maximum λ _max. = 1270 nm. All composites, with the exception of composite 7, are capable of generating singlet oxygen under the action of near UV radiation (Fig. 4) and blue light (Fig. 5). The most intense luminescence band is observed for sample 3, which contains the smallest ZnO crystals with the largest specific surface area. The experiments showed that the ability of composites 6 and 9 to photogenerate singlet oxygen is low, while this ability is not manifested at all in composite 7. These composites are not practical to use.

The slightly higher intensity of the singlet oxygen luminescence band observed in Fig. 5 when comparing the spectra shown in FIG. 4 and 5 is associated with a higher intensity of external radiation incident on the material when using a much more powerful LED with an emission wavelength of 405 nm.

Composite material 1, containing 0.74 wt.% CuO, has an average luminescent properties and an average ability to photogenerate reactive oxygen species.

Composite materials 2÷5, the compositions of which are given in table. 1 have high luminescent properties and a high ability to photogenerate reactive oxygen species.

Composite material 6, containing 0.39 wt.% CuO, has a gray tint and has an average ability to photogenerate reactive oxygen species. At the same time, its ability to convert UV-C radiation into UV-A radiation and the visible spectral range is small.

Composite 7, containing more than 1.00 wt.% CuO, was an inhomogeneous material with black inclusions. Such material cannot be used in practical applications.

Composite 8, which does not contain zinc spinel ZnAl ₂ O ₄ , has a high ability to generate reactive oxygen under the action of near UV radiation and blue light. However, its ability to convert UV-C radiation into UV-A and visible spectral range is low, as is the copper-free composite 9 .

Composite 10 containing 37.00 wt. % ZnAl ₂ O ₄ and 0.60 wt.% CuO, has a gray color, and has a fairly high ability to photogenerate reactive oxygen species. However, its ability to convert UV-C radiation into UV-A and visible spectral radiation is low.

Composite 11 containing only 62.89 wt. % ZnO, has a low ability to photogenerate reactive oxygen species.

The composite material 12 exhibits a high ability to photogenerate reactive oxygen species, but its ability to convert UV-C radiation into UV-A and visible spectral radiation is low.

Thus, the synthesized composites 2÷5 have high luminescent and bactericidal properties with a high ability to photogenerate reactive oxygen; it is advisable to use them in practical applications.

Claims (2)

Photoactive luminescent material capable of generating reactive oxygen species and able to absorb UV radiation in the wavelength range of 200-300 nm and re-emit light in the near UV (300-380 nm) and visible spectral ranges, containing ZnO, ZnAl ₂ O ₄ and CuO , characterized in that it contains ZnO nanocrystals with a size of 8-25 nm, while the components are taken in the following ratio, wt.%: ZnO 62.87-82.67 ZnAl ₂ O ₄ 17.03-36.77 CuO 0.35-0.38