Welcome to IKU Academic Digital Archive System
OpenAccess@IKU is Istanbul Kultur University's Academic Digital Archive System, established in June 2014 to digitally store and provide open access to academic and artistic outputs in line with international standards and intellectual property rights. The system includes various outputs such as articles, presentations, theses, books, book chapters, reports, encyclopedias, and works of art produced by the university's faculty members and students.
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Recent Submissions
Structural and Luminescent Properties of a Cr3+/sm3+ Doped Gdalo3 Orthorhombic Perovskite for Solid-State Lighting Applications
(Royal Society of Chemistry, 2025) Elhamdi, I.; Souissi, H.; Kammoun, S.; Dhahri, E.; Pina, J.; Costa, B. F. O.; Brito, A. L. B.; FAUSTO, RUI; Lopez-Lago, E.
The Cr3+ and Sm3+ doped GdAlO3 perovskite with formula Gd0.995Sm0.005Al0.995Cr0.005O3, was synthesized via a solid-state reaction method, and its structure, morphology, and photoluminescence properties were thoroughly investigated. The compound crystallizes in the orthorhombic Pbnm space group, with Cr3+ transition-metal ions substituting Al3+ in the octahedral symmetry site, and Sm3+ lanthanide (rare-earth) ions occupying the tetrahedral site. The material's morphology and chemical composition homogeneity were evaluated through Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray analysis. Photoluminescence excitation (PLE) and emission spectra (PL) were used to shed light on the electronic structure of the Cr3+ cations, through crystal field analysis in the Oh symmetry site. Theoretical studies enabled the precise assignment of the Cr3+ 3d-3d transitions. The intra-configurational 4f-4f transitions of Sm3+ resulted in a variety of excitation bands appearing in the high-wavelength range of the PLE spectrum. The photoluminescence studies supported the occurrence of energy transfer in the doped GdAlO3 perovskite between Gd3+, Sm3+ and Cr3+ ions. The obtained results suggest the high potential of the synthesized material for solid state lighting applications.
A Protocol for the Investigation of the Intramolecular Vibrational Energy Redistribution Problem: the Isomerization of Nitrous Acid as a Case of Study
(Royal Society of Chemistry, 2025) Duarte, Leonardo J.; Nunes, Claudio M.; FAUSTO, RUI; Braga, Ataualpa A. C.
The conformational isomerization of nitrous acid (HONO) promoted by excitation of the nu OH or nu N 00000000 00000000 00000000 00000000 11111111 00000000 11111111 00000000 00000000 00000000 O stretching normal coordinates is the first observed case of an infrared-induced photochemical reaction. The energy captured by the excited normal modes is redistributed into a highly excited vibrational level of the tau OH torsion normal coordinate, which is the isomerization reaction coordinate. Herein, we present simple numerical methods to qualitatively investigate the coupling between the normal coordinates and the possible gateways for vibrational energy redistribution leading to the isomerization process. Our methodology involves the generation of the relevant 2D potential energy surface (PES), by spanning the reaction coordinate and one of the 3N - 7 projected normal coordinates along the intrinsic reaction coordinate (IRC). Once the PES has been obtained, the time-independent wavefunctions are calculated using the standard discrete variable representation (DVR) approach. The reaction barrier is investigated using the interacting quantum atoms (IQA) decomposition scheme, evidencing an important contribution from the exchange-correlation energy to the isomerization. Coupling between normal coordinates indicates preferential normal modes to redistribute the vibrational energy. 1D deep tunneling rates were found to be negligible.
Solvatochromism and Cis-Trans Isomerism in Azobenzene-4-Sulfonyl Chloride
(Springer Nature, 2025) Sidir, İsa; Sidir, Yadigar Gülseven; Berber, Halil; FAUSTO, RUI
Solvatochromism exhibited by azobenzene-4-sulfonyl chloride (here abbreviated as Azo-SCl) has been investigated in a series of non-polar, polar-aprotic and polar-protic solvents. The UV-vis spectra of Azo-SCl exhibit two long-wavelength bands, observed at 321-330 nm (band-I) and 435-461 nm (band-II), which are ascribed to the pi*-pi (S2 <- S0) and pi*-n (S1 <- S0) transitions, respectively. The shorter wavelength band indicates a reversal in solvatochromism, from negative to positive solvatochromism, for a solvent with a dielectric constant of 32.66 (which is characteristic of methanol), while the longer wavelength band signposts negative solvatochromism in all range of solvent's dielectric constant investigated, demonstrating different interactions with the solvents in the S2 and S1 excited states. Using Catal & aacute;n and Kamlet-Taft solvation energy models, we found that the shift in the solvatochromic behavior of band-I (S2 <- S0) happens because solvent dipolarity/polarizability and hydrogen bonding affect the S2 state in opposite ways. Dipolarity/polarizability stabilizes the S2 state compared to the ground state, while hydrogen bonding destabilizes it. In contrast, for S1, both effects work together to destabilize the excited state. For all studied solvents, UV irradiation (lambda >= 311 nm; room temperature) was found to lead to fast trans-cis azo photoisomerization. In the absence of light, the photogenerated cis form quickly converts back to the trans form. Interpretation of the experimental data is supported by quantum chemical calculations undertaken within the Density Functional Theory (DFT) framework, including Time Dependent DFT calculations for excited states.
A Comprehensive Exploration of Optical Properties of GdAlO3: Cr3+
(Elsevier, 2025) Souissi, H.; Kammoun, S.; Dhahri, E.; Pina, J.; Costa, B. F. O.; Brito, A. L. B.; FAUSTO, RUI
This study focused on the optical properties of the Cr3+-doped GdAlO3 perovskite, through comprehensive analysis of its photoluminescence spectra. The GdAlO3: Cr3+ perovskite, synthesized by a traditional solid-state process, crystallizes in the orthorhombic Pbnm space group, with Cr3+ ions substituting Al3+ ions in octahedral sites. Photoluminescence excitation and emission spectra of the material were obtained and assigned. The zerophonon lines ZPL of the observed emission and excitation transitions associated with the Cr3+ ions, in the visible range, were determined, and the experimental spectral data were modelled by the Fourier transformation of the autocorrelation function, enabling the calculation of diabatic potential energy profiles for the ground and lowest energy excited states. Crystal field parameters were derived, providing insight into the electronic structure of Cr3+ in the Oh symmetry site. The results highlighted the significant impact of coordination on the electronic structure of Cr3+ ions, with a notably high nephelauxetic effect parameter (h = 1.44), indicating a high degree of covalency in the metal-ligand bonds. Energy transfer from Gd3+ to Cr3+ in GdAlO3: Cr3+ was found to be significant, contributing to the enhancement of the deep-red emission of the compound attributed to the 2Eg(2G) -> 4A2g(4F) d-d transition of Cr3+. Finally, the CIE 1931 chromaticity coordinates of the photoluminescence emission of GdAlO3:Cr3+ were determined, positioning the emission at the boundary of the chromaticity diagram, indicative of its high color purity and potential suitability for red light-emitting display applications.
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