Сравнение спектров поглощения ионов Nd-=SUP=-3+-=/SUP=- в кристаллах NdFe-=SUB=-3-=/SUB=-(BO-=SUB=-3-=/SUB=-)-=SUB=-4-=/SUB=-, Nd-=SUB=-0.5-=/SUB=-Gd-=SUB=-0.5-=/SUB=-Fe-=SUB=-3-=/SUB=-(BO-=SUB=-3-=/SUB=-)-=SUB=-4-=/SUB=- и Ho-=SUB=-0.75-=/SUB=-Nd-=SUB=-0.25-=/SUB=-Fe-=SUB=-3-=/SUB=-(BO-=SUB=-3-=/SUB=-)-=SUB=-4-=/SUB=-

Abstract

Polarized optical absorption spectra in the range of some f-f transitions of Nd3+ ions in Ho0.75Nd0.25Fe3(BO3)4, Nd0.5Gd0.5Fe3(BO3)4 and NdFe3(BO3)4 crystals were compared at 90 K. Spectral features related to difference of local environment of Nd3+ ions in the mentioned crystals were revealed. In the range of 4I9/2 → 4G5/2 + 2G7/2 transition of Nd3+ ions in Ho0.75Nd0.25Fe3(BO3)4 crystal the appearance of some absorption lines owing to the change of the local symmetry during structural transition R32 → P3121 at ~ 200 K was revealed. Their intensity increases smoothly, when the temperature decreases from the transition point. Temperature dependences of lattice parameters of Ho0.75Nd0.25Fe3(BO3)4 crystal were measured. It was found that at the transition temperature there is a discontinuous change of the lattice parameter a, which indicates a phase transition of the first order. Lattice parameter c changes smoothly.