Armenian National Academy of Sciences

About: Armenian National Academy of Sciences is a government organization based out in Yerevan, Armenia. It is known for research contribution in the topics: Population & Laser. The organization has 4090 authors who have published 4042 publications receiving 40828 citations. The organization is also known as: Armenian National Academy of Sciences & NAS RA.

Modeling the crystal-field splitting of the energy levels of Er 3+ in charge-compensated sites in lithium niobate

Abstract: We have calculated the crystal-field splitting of the energy levels of Er 31 (4f 11 ) in charge-compensated sites having C3 symmetry in the host crystal of lithium niobate, LiNbO3 ~LN!, with crystal-field parameters obtained from lattice-sum calculations. The charge-compensation model assumes that Er 31 substitutes into Li 1 sites that are shifted from the Li 1 positions in the undoped lattice with excess charge compensated for by niobium vacancies and defect complexes. The calculated splitting of 11 multiplet manifolds 2S11 LJ including the ground state 4 I 15/2 of Er 31 (4f 11 ) is compared with existing data in the literature, as well as with polarized absorption and fluorescence spectra obtained in the present study betwee n 8 K and room temperature. The calculated splitting is compared with the experimental splitting without least-squares adjustments to the crystal-field splitting parameters, although the centroids between multiplet manifolds are adjusted to account for J mixing between states. The calculated splitting supports site symmetries for Er 31 as C3 , in agreement with magnetic resonance studies. The calculation also predicts the symmetry label of the ground-state Stark level as 2 G 6 or m~63/2!, in agreement with the observed polarized absorption and fluorescence spectra.

Progressive orocline formation in the Eastern Pontides–Lesser Caucasus

Abstract: The Eastern Pontides–Lesser Caucasus fold–thrust belt displays a peculiar northwards arc-shaped geometry that was defined as an orocline in earlier studies. The Lesser Caucasus was affected by two main tectonic events that could have caused orocline formation: (1) Paleocene–Eocene collision of the South Armenian Block with Eurasia; and (2) Oligocene–Miocene Arabia–Eurasia collision. We tested the hypothesis that the Lesser Caucasus is an orocline and aimed to time the formation of this orocline. To determine the vertical axis rotations, 37 sites were sampled for palaeomagnetism in rocks of Upper Cretaceous–Miocene age in Georgia and Armenia. In addition, we compiled a review of c. 100 available datasets. A strike test was applied to the remaining datasets, which were divided into four chronological sub-sets, leading us to conclude that the Eastern Pontides–Lesser Caucasus fold–thrust belt forms a progressive orocline. We concluded that: (1) some pre-existing curvature must have been present before the Late Cretaceous; (2) the orocline acquired part of its curvature after the Paleocene and before the Middle Eocene as a result of South Armenian Block–Eurasia collision; and (3) about 50% of the curvature formed after the Eocene and probably before the Late Miocene, probably as a result of Arabia–Eurasia collision.

4f2 to 4f5d excited state absorption in Pr3+:YAlO3

Abstract: Excited-state absorption spectra, from the 3PJ -1I6 or 1D2 manifold to 4f5d levels, recorded in the 23 000-42 000 cm 1 range and calibrated in units of cross sections, are reported and discussed in the case of Pr 3+ -doped YAlO3. The 4f5d! 4f 2 Pr 3+ emission between 30 000 and 44 000 cm 1 is then observed, showing the possibility of UV laser operation following two-step excitation pumping using near-UV-visible pump photons.