Delhi Technological University

About: Delhi Technological University is a education organization based out in New Delhi, India. It is known for research contribution in the topics: Computer science & Control theory. The organization has 4427 authors who have published 6761 publications receiving 71035 citations. The organization is also known as: Delhi College of Engineering & DTU.

Spin mixed charge transfer states of iridium complex Ir(ppy)3: transient absorption and time-resolved photoluminescence

Abstract: Nanosecond transient absorption and time-resolved spectroscopic techniques were applied to study an organometallic phosphorescent emitter Ir(ppy)3 complex, tris[2-phenylpyridinato-C2,N] iridium(III) dissolved in tetrahydrofuran (THF) under degassed conditions at ambient temperature. Transient absorption curves obtained at a pump pulse of 355 nm and at a probe wavelength of 430–600 nm show positive and negative signals, indicating triplet–triplet (T–T) absorption and triplet–singlet (T–S) emission. Tri-exponential global fitted transient absorption curves and time-resolved photoluminescence (PL) decays demonstrated the presence of four close low lying triplet states, of which, two emit green PL with a lifetime of 210 ns and 1.71 μs. The emitting states are spin mixed metal-to-ligand charge transfer (3MLCT) states produced from a non-equilibrium 1MLCT state following fast intersystem crossing (ISC), whereas the 1MLCT state is produced directly and indirectly depending on the excitation wavelength. Moreover, the electronic structures for the ground state and low-lying excited states of Ir(ppy)3 were studied using quantum chemistry calculations.

Bianchi type-V cosmological models with perfect fluid and heat flow in Saez-Ballester theory

Abstract: In this paper we discuss the variation law for Hubble’s parameter with average scale factor in a spatially homogeneous and anisotropic Bianchi type-V space-time model, which yields constant value of the deceleration parameter. We derive two laws of variation of the average scale factor with cosmic time, one is of power-law type and the other is of exponential form. Exact solutions of Einstein field equations with perfect fluid and heat conduction are obtained for Bianchi type-V space-time in these two types of cosmologies. In the cosmology with the power-law, the solutions correspond to a cosmological model which starts expanding from the singular state with positive deceleration parameter. In the case of exponential cosmology, we present an accelerating non-singular model of the Universe. We find that the constant value of deceleration parameter is reasonable for the present day Universe and gives an appropriate description of evolution of Universe. We have also discussed different types of physical and kinematical behaviour of the models in these two types of cosmologies.

Some frw models of accelerating universe with dark energy

Abstract: The paper deals with a spatially homogeneous and isotropic FRW space-time filled with perfect fluid and dark energy components. The two sources are assumed to interact minimally, and therefore their energy momentum tensors are conserved separately. A special law of variation for the Hubble parameter proposed by Berman (Nuovo Cimento B 74:182, 1983) has been utilized to solve the field equations. The Berman’s law yields two explicit forms of the scale factor governing the FRW space-time and constant values of deceleration parameter. The role of dark energy with variable equation of state parameter has been studied in detail in the evolution of FRW universe. It has been found that dark energy dominates the universe at the present epoch, which is consistent with the observations. The physical behavior of the universe has been discussed in detail.