Application of photoconductivity measurements to photodynamic processes investigation in LiYF4:Ce3+ and LiLuF4:Ce3+ crystals

Abstract Photoconductivity measurements are applied to the studies of photodynamic processes in LiYF 4 :Ce 3+ and LiLuF 4 :Ce 3+ crystals undergoing ultraviolet irradiation. Photoconductivity spectra were registered by means of microwave technique under irradiation at 220–320 nm at the room temperature. Photoconductivity signal appeared at ∼300 nm and monotonically increased with the shortening of wavelength. Pumping energy dependencies of photoconductivity within 225–305 nm spectral range were registered and revealed the change of the dependence degree from quadratic at longer wavelengths through linear to saturation-like at shorter ones. Numerical simulation based on four-level model of photodynamic processes was performed. Values and spectral distributions of probabilities of different types of photodynamic processes for 225–295 nm were estimated. Ce 3+ ions excited-state photoionization cross-section spectra in both investigated materials revealed a band with a peak around 270 nm most probably corresponding to 5d–6s transition of Ce 3+ . Recombination cross-section in Ce:LiLuF 4 appeared to be two orders of magnitude higher than in Ce:LiYF 4 . A complete energy level diagram of “Ce 3+ ion–LiYF 4 crystal” system has been proposed.