Аннотация:Тhe purpose of this work was to synthesize non-luminescent PAAO and study the PL of the test analyte in the pores of the samples. Rhodamine B was chosen as the analyte.We will use the following designations for the samples, prepared in sulfuric acid: S5 (initial), S5-R1 (with Rhodamine B 10−5 M), S5-R2 (with Rhodamine B 10−6 M), S5-R3 (with Rhodamine B 10−7 M) and for the samples, prepared in selenium acid: Se5 (initial), Se5-R1 (with Rhodamine B 10−5 M), Se5-R2 (with Rhodamine B 10−6 M), Se5-R3 (with Rhodamine B 10−7 M).It is evident that the average pore diameter of the samples varies from 9 to 15 nm. Quite a large deviation in size can be explained by the elongated shape of some samples, probably due to the merging of two "seed" pores into one during the formation of PAAO. The thickness of the porous layer is 7.5 μm. No structural changes are observed when the dye is applied. Also, no large dye clusters or films are observed on the oxide surface, indicating that the dye was adsorbed exclusively on the sample surface. The samples acquire a stable pinkish tint that is not removed by washing.Raman spectroscopy studies showed that the samples had an amorphous structure.The initial PAAO (S5 and Se5) did not luminesce. Therefore, the obtained PAAO samples can be used for the analysis of the PL of the analyte (dye) in the pores of PAAO. S5-R1 and Se5-R1 samples demonstrated intense PL of rhodamine B in the range of 530-680 nm with a PL maximum at 573 nm.The PL intensity of the dye increased sharply starting from the Rhodamine B concentration of 10-5 M in the samples synthesized both in sulfuric acid and in selenium acid. At low dye concentrations (10-7-10-6 M), the PL intensity was approximately the same for both types of samples. However, the PL intensity of the dye for the S5-R1 samples was more than 4 times higher than the PL intensity for the Se5-R1 samples. To identify the cause of such a significant difference, we studied the samples by EPR to identify the type of defects and determine their concentration. It was found that the main type of defects in the S5-R1 samples were oxygen vacancies with an unpaired electron (F+ centers, g=2.0020±0.0005). The concentration of F+ centers was Ns=3·1015 g-1. In the Se5-R1 samples, paramagnetic complexes of the Al-SеO3 type were found, which were built into the aluminum oxide structure from the electrolyte. F+ centers were also found in the Se5-R1 samples. The total defect concentration was Ns=9.2 1016 g-1. It can be assumed that the decrease in the dye PL intensity by several times in the Se5-R1 films compared to S5-R1 is due to an increase in the contribution of nonradiative recombination of photoexcited charge carriers on the detected paramagnetic defects, the concentration of which is more than an order of magnitude higher in the Se5-R1 films.Thus, the exciting radiation is absorbed not only by the dye, but also by defects in the porous aluminum oxide structure.These results are important for the creation of an optical sensor platform based on porous aluminum oxide.
