Ranajit K. Mukherjee

Spectra of Benzil

The polarized low‐temperature absorption spectrum, emission spectrum, and excitation spectrum of benzil and benzil‐doped stilbene crystals have been recorded. It has been found that the 3800 A (n–π*) band system of benzil is split by the weak interaction between the two halves of the molecule. The excitation spectrum reveals the presence of a S→T transition hidden underneath the S→S transition. The crystal spectrum of benzil‐doped stilbene is different from the benzil spectrum. The new sharp band at 4850 A has been interpreted in terms of a trans–planar configuration of benzil. A weak (π*→n) fluorescence has been detected in this crystal.

Effect of Li doping on the magnetotransport properties of La0.7Ca0.3−yLiyMnO3 system: Decrease of metal–insulator transition temperature

With increasing the Li doping level in La0.7Ca0.3−yLiyMnO3 (0⩽y⩽0.3), the system is driven from a higher-conductivity regime to a lower-conductivity regime, which is in sharp contrast with the behavior of Na or K doping. Compared to those of K or Na, the ionic radius of Li is much smaller than that of Ca. Therefore, substitution of Ca by Li results in a smaller average A-site radius, narrowing the bandwidth and hence enhancing the band gap and resistivity. The effect of random disorder of La3+ and A2+ also plays an important role leading to charge localization.

Thermoelectric power of Na-doped La0.7Ca0.3−yNayMnO3 both in the presence and the absence of magnetic field

Magnetic-field (B=0–1.5 T) dependent thermoelectric power (TEP) of the Na-doped La0.7Ca0.3−yNayMnO3 (0.0⩽y⩽0.3) system has been studied in the temperature range 80–300 K. X-ray diffraction studies indicate a rhombohedrally distorted perovskite structure of the samples. The observed sharp peak in the resistivity (ρ) versus temperature (T) curve falls and shifts to higher temperature with increasing Na concentration (y). In the low-temperature ferromagnetic (FM) regime, thermopower (Seebeck coefficient, S) obeys the expression S=S0+S1.5T1.5+S4T4 over the entire range of y. Electron-magnon scattering is found to dominate the low-temperature resistivity and TEP data. High-temperature TEP data can be well fitted with Mott’s small polaron hopping model. The activation energy (ES) and polaron hopping energy (WH) decrease with increasing Na content. Both ES and WH decrease while polaron radius (rp) increase with the application of a magnetic field. Field-dependent TEP data also indicate the suppression of spin fl...

7F0-5D1 transition in Eu3+—hexakisantipyrene-triiodide single crystal. A magnetic dipole transition

Abstract The polarised absorption spectrum of Eu3+—hexakisantipyrene-triiodide (HAPI) at 77 K along with a Zeeman effect study is reported. The7F0 →5D1 transition has been found to be magnetic dipole allowed. The g value of 1.48 ± 0.06 for the5D1 state is in fair agreement with the g value of the free ion. This fact together with the absence of any vibronic band (unlike other HAPI crystals) is indicative of negligible covalent character of the Eu O bond.

Absorption spectroscopy of Eu3+ ions in CsCdCl3 crystal: an evidence of nonequivalent sites

Abstract The polarized optical absorption study of Eu 3+ ions in a CsCdCl 3 crystal reveals an interesting behaviour in their electronic energy levels. In the crystal the trivalent Eu 3+ ions replace the divalent Cd 2+ ions; in order to maintain the charge neutrality the Eu 3+ ions associate in pairs accompanying one vacancy. Our observation shows that the Eu 3+ ions form two types of pair: (i) Eu 3+ –vacancy–Eu 3+ ; and (ii) vacancy–Eu 3+ –Eu 3+ , and the Eu 3+ ions feel two different trigonal ( C 3v ) electrostatic crystal fields in these two types of pair. As a result they produce pair-type of absorption spectra for each energy level. The occurrence of two distinct lines corresponding to 7 F 0 → 5 D 0 transition elucidates the presence of two nonequivalent sites in the crystal.

Zeeman spectroscopy of Nd3+ ions in CsCdCl3 crystal

A transverse Zeeman study of the high-concentration Nd3+-doped CsCdCl3 crystal at 25 K in an external magnetic field of 7.8 T applied both parallel and perpendicular to the c axis, is presented here. Observed splittings of the transitions 4I9/2→4G5/2 and 4I9/2→2G7/2 of the 4f3 electronic configuration of Nd3+ ions are investigated in detail. From the observed splittings for B‖c, the parallel splitting factors s‖ are determined for the levels in these multiplets. But for B⊥c no resolvable splitting is found at any level in these two multiplets.

Magnetic studies on low-spin K3Mn(CN)6

Abstract This work reports measurements on single crystals of K3Mn(CN)6, of the magnetic susceptibilities and their anisotropies between 300 and 80K. The crystal field model has been extended to include molecular overlap effects for this highly covalent low-spin compound. The magnetic data explain the occurrence of the hot bands around 18,000 cm−1 reported earlier[1].

The g-value of the 2E state of K3CR(CN)6 and the lower symmetry field

Abstract The 4 A 2 → 2 E transition of potassium chromicyanide has been studied under magnetic field. It has been found that the g -value is nearly isotropic, quite unlike the case of ruby. An attempt has been made to explain the zero-field splittings of 2E , 2 T 1 and 2 T 2 states and the g -value of the 2 E state on the assumption that the distant ions are mainly responsible for lowering of symmetry of the crystal field from O h . A reasonable choice of parameters can make the calculated values agree with the observed ones.

Polarized absorption spectra of Co2+ in Na2Cd3Cl8 single crystals

SummaryThe polarized optical absorption spectra of Na2Cd3Cl8: Co2+ in the range of 15 000 to 40 000 cm−1 down to 15 K are reported. The Co2+ ion is found to occupy the Cd2+ sites in octahedral geometry and the spectra are interpreted satisfactorily in terms of a cubic ligand field model including spin-orbit coupling. The observed crystal field spectra are well reproduced withB=745 cm−1,C=3410 cm−1,Dq=700 cm−1 and ζ (spin-orbit interaction) =520 cm−1. No spectral evidence for tetragonal distortion is observed.

POLARIZED ABSORPTION SPECTRA OF NICKEL ION IN MAGNETIC TRIMETHYL AMMONIUM NICKEL TRICHLORIDE DIHYDRATE (NiTAC) [(CH3)3NH]NiCl3.2H2O SINGLE CRYSTALS

Abstract The low temperature polarized absorption spectra of the Ni 2+ ions in the orthorhombic [(CH 3 ) 3 NH]NiCl 3 .2H 2 O NiTAC single crystal have been reported at 300 K and 15 K. The polarization spectra show the presence of a lower field (D 4 ) which is rather small to split the levels. A moiety vibration of 370 cm −1 has been observed. No magnon or magnon-phonon side bands are observed.