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In this study we report on the results from emission $^{57}$FeM${\"o}$ssbauer Spectroscopy experiments, using dilute $^{57}$Mn implantationinto pristine (TiO$_2$) and hydrogenated anatase held at temperatures between300-700 K. Results of the electronic structure and local environment arecomplemented with ab-initio calculations. Upon implantation both Fe$^{2+}$ andFe$^{3+}$ are observed in pristine anatase, where the latter demonstrates thespin-lattice relaxation. The spectra obtained for hydrogenated anatase show noFe$^{3+}$ contribution, suggesting that hydrogen acts as a donor. Due to thelow threshold, hydrogen diffuses out of the lattice. Thus showing a dynamicbehavior on the time scale of the $^{57}$Fe 14.4 keV state. The surroundingoxygen vacancies favor the high-spin Fe$^{2+}$ state. The sample treated atroom temperature shows two distinct processes of hydrogen motion. The motioncommences with the interstitial hydrogen, followed by switching to thecovalently bound state. Hydrogen out-diffusion is hindered by bulk defects,which could cause both processes to overlap. Supplementary UV-Vis andelectrical conductivity measurements show an improved electrical conductivityand higher optical absorption after the hydrogenation. X-ray photoelectronspectroscopy at room temperature reveals that the sample hydrogenated at 573 Kshows presence of both Ti$^{3+}$ and Ti$^{2+}$ states. This could imply that asignificant amount of oxygen vacancies and -OH bonds are present in thesamples. Theory suggests that in the anatase sample implanted with Mn(Fe),probes were located near equatorial vacancies as next-nearest-neighbours,whilst a metastable hydrogen configuration is responsible for the annealingbehavior.

Experimental and theoretical study of electronic and hyperfine properties of hydrogenated anatase (TiO$_2$): defects interplay and thermal stability