D. Ramachandra Rao

Electron paramagentic resonance and phase transitions in Mn2+ doped Cd(ClO4)2⋅6H2O

An electron paramagnetic resonance study of Mn2+ doped in Cd(ClO4)2⋅6H2O has been made from 328 K to liquid nitrogen temperature. The site symmetry of Cd2+ is trigonal with a water octahedron distorted parallel to the crystallographic c axis. Mn2+ substitutes for Cd2+ and exhibits a characteristic 30‐line hyperfine spectrum at room temperature (298 K) for the magnetic field H along the c axis. The D parameter is small and therefore there is considerable overlapping of lines in the spectrum. The spectrum is axially symmetric. On lowering the temperature, phase transitions are found to occur at 272±1 and 115.5±1 K.

Laser induced fluorescence in CO2, (CO2 + 14N2), (CO2 + 15N2) and (CO2 + He)

Abstract Vibrational deactivation in CO 2 ( v 3 mode) is studied extensively in CO 2 , CO 2 + 14 N 2 , CO 2 + 15 N 2 and CO 2 + H by use of the laser induced fluorescence technique covering the entire range of concentration (0–100 per cent) in the temperature range 300–500°K. While the data on composition yield better average values for the specific rate constants involved, the study with temperature is found to be consistent with the SSH theory.

Electron paramagnetic resonance study of Mn2+-doped iron, cobalt, and nickel perchlorate hexahydrates

Abstract Mn 2+ -doped Fe(CIO 4 ) 2 ·6H 2 O, Co(ClO 4 ) 2 ·6H 2 O, and Ni(ClO 4 ) 2 ·6H 2 O have been studied by EPR from room temperature to liquid nitrogen temperature. Mn 2+ replaces the metal ions at sites of trigonal symmetry. The EPR lines are broad and the D parameters are small; thus, there is considerable overlap in the spectra. The spectra are nearly axially symmetric. The temperature variation study shows phase transitions at 237 ± 5, 154.5 ± 6.5, and 223 ± 5 K in iron, cobalt, and nickel perchlorate hexahydrates, respectively.

Stimulated Raman spectra of H2O and D2O

Abstract SRS of the valence band of liquid H 2 O and D 2 O are obtained using a nanosecond pulse from a Q -switched ruby laser. The SRS contours obtained are in overall agreement with those of earlier workers using picosecond pulses and help clarify the results of one of the published works. The broad SRS bands are less likely to be attributed to self-focusing in water, but to the stimulation of overlapping components.

Steady state and transient fluorescence studies of CaF2: Dy3+ single crystals

The steady state and transient fluorescence spectra of CaF2: Dy3+ have been studied using Ar+ and N2 lasers in the temperature range 77–673 K and in the wavelength region 4500–9000 A. The spectra show the presence of two types of centers (type A and type B) with decay times of 1.3 and 3.5 ms. The observed spectrum is mostly due to type A centers. Three new groups of fluorescence 4F92−6H112, 4F92−(6H92, 6F112) and 4F92−(6H72, 6F92) have been observed for type A centers, and a tentative assignment of the positions of the Stark levels of 6H112, (6H92, 6F112) and (6H72, 6F92) has been made. The change in the intensity of the transitions with temperature and excitation wavelength are discussed.

Electronic spectrum of NSe

Abstract Isotope shift studies and fine structure analysis of the emission spectrum observed in the visible region have established the existence of the NSe molecule. Molecular constants are reported identifying the transition as 2 π r - X 2 π r . The nature of the molecular formation and heat of dissociation are discussed.

Emission spectrum of Te2

Abstract The analysis of high resolution emission spectra of isotopic enriched 130Te2 gave the rotational constants suggesting the transition as a σ - σ type. Heat of dissociation of Te2 is evaluated from the computed dissociation limit in the excited state.

Fluorescence and lifetime studies of Ho3+: CaF2

Abstract Four fluorescence groups in the wavelength region 4775–7590 A have been recorded in Ho3+: CaF2 single crystals in the concentration range from 0.01 to 0.1 wt% of Ho3+. The observed variation of the relative intensities of various fluorescence lines with concentration indicate the presence of more than one Ho3+ site in CaF2. This has been further substantiated by the observation of three different fluorescent decay times. The increase in the fluorescent decay times with concentration above 373 K is explained as probably being due to reabsorption of fluorescence radiation.

Radiative decay rates in LaF3:Dy3+

Abstract The decay times of fluorescence from 4 F 9/2 and 4 I 15/2 levels of LaF 3 :Dy 3+ single crystals have been measured in the temperature range 77 to 673 K. The decay rate of 4 F 9/2 is found to be 720s −1 and that of 4 I 15/2 is calculated to be less than 1.5 × 10 3 s −1 .

Multiphonon relaxations in Ho3+: LAF3 single crystal

Abstract The mulliphonon transition rates in Ho 3+ :LaF 3 are estimated from the observed fluorescence decay rates of the states 5 F 3 and ( 5 F 4 , 5 S 2 ), in the temperature interval 80–675°K. The data is analyzed in terms of the existing theoretical models. The analysis indicates that the high energy phonons play a dominant role in these multiphonon transitions.