IR spectra were recorded using Nicolet iN10 MX FTIR microscope for samples in the form of nujol mulls pressed between two 1.0 mm thick BaF2 plates. UV-vis experiments were done using Shimadzu UV-3600i Plus spectrophotometer in the transmission mode for samples in the form of nujol mulls pressed between two 1.0 mm thick quartz plates. The irradiation experiments presented in Figure and 7 were performed using power led diodes as described in the "Magnetic measurements" section without removing the samples from the instruments (in-situ). . The solid lines are the best fits to generalized Debye model.