Random laser action in dye-doped xerogel with inhomogeneous TiO₂ nanoparticles distribution

Rhodamine 6G-doped TEOS-derived xerogels containing different concentrations of TiO₂ nanoparticles with average diameter of about 350 nm were designed to study random laser action. Due to the decantation of TiO₂ nanoparticles during the sol–gel process, the obtained xerogels samples exhibits an inhomogeneous TiO₂ distribution, with a higher concentration at one of the sample surfaces. By pumping the samples at each of the surfaces at a time with a ps-laser at 532 nm, differences in the emission behavior were observed. The higher concentration of TiO₂ in one side of the sample, which occurs during its preparation, was shown to play an important role in the random laser energy threshold and emission spectra, depending on what side of the sample the excitation takes place. The difference in the laser threshold shows that the way scatterers are volumetrically distributed can increase or decrease the pump energy required for laser action.