A.V. Malakhovskii

Magneto-optical properties of Dy3+ in oxide glasses: The origin of the magneto-optical activity of f-f transitions and its anomalous temperature dependence

The temperature dependence of the absorption spectra and magnetic circular dichroism due to f-f transitions from the 6H15/2 to 6F5/2 and 6(F7/2 + H5/2) states in the Dy3+ ion in (Dy2O3-P2O5-SiO2-GeO2) and (Dy2O3-La2O3-Al2O3-B2O3-SiO2-GeO2) glasses and the temperature dependence of the Faraday effect were studied. The temperature dependence of the Faraday effect caused by f-d transitions was found to differ from that of the magnetic circular dichroism due to f-f transitions. It was shown that f-f transitions occur preferentially in Dy3+ ions associated into clusters. The origin of the paramagnetic magneto-optical activity of f-f transitions was analyzed. It was shown that the contributions to this activity can differ in value and sign and that the ratio between these contributions depends on the transition type. In some cases, this difference results in an anomalous temperature dependence of the magneto-optical activity.

Spectroscopic properties and structure of the ErFe3(BO3)4 single crystal

Single crystals of the ErFe3(BO3)4 borate were synthesized and their structure was studied. Absorption spectra of the Er3+ ion in σ- and π-polarizations of f-f transitions 4I15/2 → 4I13/2, 4I11/2, 4I9/2, 4F9/2, 4S3/2, 2H11/2, and 4F7/2 were measured. The refractive index and birefringence were measured as a function of the wavelength. The transition intensities were analyzed within the Judd-Ofelt theory, and the following parameters of the theory were obtained: Ω2 = 7.056 × 10−20 cm2, Ω4 = 1.886 × 10−20 cm2, and Ω6 = 2.238 × 10−20 cm2. Using these parameters, the radiative transition probabilities, luminescence branching ratios, and radiative lifetimes of multiplets were calculated.

Magnetic properties of the Nd0.5Gd0.5Fe3(BO3)4 single crystal

The magnetic properties of the Nd0.5Gd0.5Fe3(BO3)4 single crystal have been studied in principal crystallographic directions in magnetic fields to 90 kG in the temperature range 2–300 K; in addition, the heat capacity has been measured in the range 2–300 K. It has been found that, below the Néel temperature TN = 32 K down to 2 K, the single crystal exhibits an easy-plane antiferromagnetic structure. A hysteresis has been detected during magnetization of the crystal in the easy plane in fields of 1.0–3.5 kG, and a singularity has been found in the temperature dependence of the magnetic susceptibility in the easy plane at a temperature of 11 K in fields B < 1 kG. It has been shown that the singularity is due to appearance of the hysteresis. The origin of the magnetic properties of the crystal near the hysteresis has been discussed.

Giant natural circular dichroism of vibronic transitions in HoAl3(BO3)4

The giant natural optical activity of vibronic replicas of the f–f5I8 → 5F2 transition in HoAl3(BO3)4 is observed. It exceeds the optical activity related to purely electronic transitions by two orders of magnitude and corresponds to the almost complete circular polarization of the transitions. This effect is explained by the local distortions of the crystal in the excited electronic state, which lead to the mixing of electron and vibrational wavefunctions and, as a consequence, to the delocalization of the vibronic wavefunction and the enhancement of spatial dispersion, which is responsible for the optical activity.

Magnetic and natural optical activity of f–f transitions in multiferroic Nd0.5Gd0.5Fe3(BO3)4

Spectra of absorption, magnetic circular dichroism, and natural circular dichroism of the f–f transitions 4I9/2 → 4F3/2, 2H9/2 + 4F5/2, 4S3/2 + 4F7/2, 2G7/2 + 4G5/2, 2K13/2 + 4G7/2, and 4G9/2 in the Nd3+ ions in the Nd0.5Gd0.5Fe3(BO3)4 crystal have been measured as a function of the temperature in the interval of 90–300 K. Temperature dependences of the magneto-optical activity (MOA) and natural optical activity (NOA) of the transitions have been obtained. It has been found that, in contrast to allowed transitions, the temperature dependence of the MOA of the f–f transitions does not obey the Curie–Weiss law and the NOA depends on temperature. The NOA of some transitions changes the sign with variation in temperature. These phenomena have been explained by the presence of three contributions to the allowance of the f–f transitions, which lead to three contributions of different signs to the MOA and NOA. The range of the MOA of the f–f transitions in the Nd3+ ion has been predicted theoretically and confirmed experimentally.