## Materials and Methods
### Characterization Methods  
TiO\({}_{2}\) samples were characterized by X-ray diffraction (Mini Flex Benchtop 300/600, 150) by using Cu K\(\alpha\) irradiation from 10\({}^{\circ}\) to 80\({}^{\circ}\) at a scan rate of 2\({}^{\circ}\)/min. Analysis of phase composition was performed by the Rietveld refinement method (High Score Plus software). The semi-quantitative chemical analysis was based on energy-dispersive X-ray (EDX) by means of a field emission scanning electron microscope (JSM-7100F, JEOL, Japan) equipped with an EDX detector (X-Max80, OXFORD, UK). From nitrogen adsorption isotherms at 77 K on a Micromeritics Tristar 300 instrument, the specific surface areas of the powder samples were calculated. Nitrogen was used as the adsorbate gas. The amount of adsorbed gas is correlated to the total surface area of the particles, including pores in the surface. The calculation was based on the BET theory. The reflectance spectra of the examined samples were recorded on a dual-beam spectrophotometer (PERKIN ELMER, model Lambda 650, USA) with a wavelength range of 350-500 nm. The beam deflection spectrometry (BDS) was performed with a home-built experimental setup, presented in Figure 1.  
The examined sample was illuminated by an intensity-modulated light beam (excitation beam) (EB) from a solid state laser (Coherent, OBIS 405 nm, USA) with 50 mW output power to provide high light absorption in the TiO\({}_{2}\)-based sample. The EB was modulated by a mechanical chopper (SCIENTIC INSTRUMENTS, USA, Control unit model 300C, chopping head model 300 CD, chopping disk model 300H), focused by a lens of 100 mm focal length (LB1676-A, Thorlabs, USA) and directed by a mirror (BB1-E02, Thorlabs, USA) to hit the sample perpendicularly to its surface. The sample was placed on a 3D translation stage (CVI, Model 2480M/2488, USA) to vary its position in the x, y and z directions and to optimize the experimental configuration. The absorbed energy induced temperature oscillations (TOs) not only in the sample but also in its surroundings. The TOs were probed by a PB (543.1 nm) from a He-Ne laser with 2 mW output power (MELLES GRIOT, Model 25-LGR-393-230, USA). The interaction of the PB with TOs resulted in PB deflections, which were detected by a quadrant photodiode (RBM-R. Braumann GmbH, Model C30846E, Germany) equipped with an interference filter (632 nm CWL, Edmund Optics) and connected to a lock-in amplifier (Stanford research instruments, Model SR830 DSP, USA). To optimize the experimental setup, the PB was slightly focused by a lens of 50 mm focal length (LB1471-A, Thorlabs, USA) and carefully aligned close to the sample surface, just to skim it. For this reason, the measurements were performed on flat samples with small lateral dimensions, which were larger than the PB diameter (\(\sim\)100 \(\upmu\)m radius). The TLS experimental setup used for RB19 degradation measurements is presented in Figure 2. The EB was a diode-pumped 532 nm laser (MGL-III-532-100, UltraLasers. Canada) with 25 mW output power controlled by the neutral density filter (NDF). The laser beam was collimated and focused onto a spot of 20 \(\upmu\)m in diameter in the center of the sample by a set of lenses, L3, L4 and L5, with focal lengths of 30, 150 and 100 mm (LB1757-A, LB1437-A, LB1676-A, Thorlabs, USA), respectively. The EB was modulated at 1 Hz by a signal generator (RIGOL DG1022, RIGOL Technologies, Inc., USA). The absorbed energy was converted into heat, and as a result, the refractive index of the sample changed, thus inducing the so-called thermal lens (TL) effect in the sample. The TL effect was probed by a PB from a He-Ne laser (632.8 nm, 3 mW, 05-UR-111, [PERSON]) that was collimated to a size of 3 mm in diameter by a set of lenses with focal lengths of 30 and 150 mm (LB1757-A, LB1437-A, Thorlabs, respectively). Both beams were directed coaxially through the sample using a dichroic mirror DM (DMSP605, Thorlabs).