Aerogels are materials that are a gel in which the liquid phase is completely replaced by a gaseous one. As a result, the substance has a record low density, as well as a number of other unique qualities: they are durable (an airgel sample can withstand a load 2000 times its own weight), have extremely low thermal conductivity and a developed specific surface area. All this allows the use of aerogels for a wide range of tasks. For example, heat-insulating materials for industrial use are made on the basis of such materials. In addition, aerogels can also have a number of useful biological properties, which makes them a promising material for use in biomedicine.
One of the most urgent tasks in this area today is the search for new luminescent agents, which will solve the problems of bio-imaging and early diagnosis of diseases. In most materials used, luminescence occurs by the usual mechanism: radiation with a short wavelength is absorbed, and emitted in the long-wavelength part of the spectrum.
However, it is possible to create a fundamentally new class of materials that are capable of converting infrared radiation into visible radiation due to the phenomenon of up-conversion. In this case, the conversion occurs due to the addition of two or more long-wavelength photons with low energy into one with higher energy.
In the development of such materials with upconversion properties, rare earth complexes are used. This is a complex process that involves synthesis in several stages. Scientists from the SCAMT international scientific laboratory at ITMO University have developed a simpler, universal method for producing up-conversion aerogels based on metal oxides (zirconium, hafnium and tantalum) doped with rare-earth elements of erbium and ytterbium.
Carefully selected synthesis conditions made it possible to obtain materials with uniformly included dopants in the oxide structure (modifying additives necessary to impart optical properties to the material) and unique luminescent characteristics.
“ It is known that luminous aerogels can be obtained using rare earth elements. But in this case, it is necessary to create a hybrid material, that is, mix two phases. For the first time, we managed to introduce ions of rare-earth elements into the oxide lattice in one stage and obtain a monolithic up-conversion airgel - in our case, only the oxide phase is visible on the spectrum, absolutely without impurities , ”says Grigory Kiselev , the first author of the article, an employee of the international laboratory SCAMT.
Initially, the researchers obtained luminous zirconium oxide by doping the oxide matrix with rare-earth elements, after which they managed to obtain an airgel of this material. Having worked out the technology, they applied it to obtain airgels and for other materials by the same analogy. In particular, scientists at the SCAMT laboratory successfully tested the method using hafnium oxide and tantalum oxide, and showed that luminous aerogels can also be created on their basis. In the future, as the authors of the study note, this method can also be applied to other oxides.
The combination of such properties as biocompatibility, high surface area and upconversion luminescence open up a wide range of possible applications of the materials obtained: from optics and photonics to medicine, ”adds Grigory Kiselev .
First of all, the use of such materials is safe for humans: infrared radiation can penetrate into biological tissues to the maximum depth without damaging them. In addition, with IR excitation, the autoluminescence of biological tissues is minimized, which makes it possible to increase the accuracy of studies. All this makes such materials promising for use, for example, as luminescent probes in biological research and for fluorescence diagnosis and treatment of cancer.
Article: Upconversion Metal (Zr, Hf, Ta) Oxide Aerogels, Kiselev Grigorii; Kiseleva Aleksandra; Ilatovskii Daniil; Koshevaya Ekaterina; Nazarovskaia Daria; Gets Dmitry; Vinogradov Vladimir; Krivoshapkin Pavel; Krivoshapkina Elena, Chemical Communications, DOI: 10.1039 / c9cc02452b, 2019
Elena Menshikova - News portal editorial staff