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3 doped with different concentrations of cerium and nitrogen
Published in Domenico Lombardo, Ke Wang, Advances in Materials Science and Engineering, 2021
G.W. Pang, D.Q. Pan, C.X. Liu, L.Q. Shi, X.D. Wang, L.Z. Liu, J.B. Liu, L. Ma, L.L. Zhang, B.C. Lei
The band gap of N@O&3Ce@3Ta system is 2.295 eV, which is larger than that of pure NOT. This is due to the excessive concentration of doping elements, which severely destroys the integrity of the crystal. Due to the electric imbalance around the impurities, a crystal field is formed. Under the action of the crystal field, energy level splitting occurs. Concurrently, impurity levels [34] are formed near the Fermi level, and the energy difference between the Fermi level and the top of the valence band and the bottom of the conduction band is 0.802 eV and 1.376 eV, respectively. In fact, deep energy levels near the center of the forbidden gap often form an effective recombination center, which promotes the recombination of non-equilibrium carriers and plays an important role in enhancing the photoelectric and luminescent properties of semiconductors [35]. It can be seen from the density of states (DOS) in Figure 4 that the impurity energy level is mainly formed by the contribution of the N-2p state. The increased forbidden band can be divided into two small forbidden bands, which become the bridge of the electronic transition from valence band to conduction band. A small amount of energy can cause a transition to the impurity level and then to the conduction band. Due to the reduced energy required, NOT can respond to low-energy visible light, i.e., its photocatalytic efficiency is improved.
Crystals and Glasses
Published in Marvin J. Weber, and TECHNOLOGY, 2020
Merritt N. Deeter, Gordon W. Day, Allen H. Rose
By definition, magnetooptic effects are those effects in which the optical properties of certain materials are affected by applied magnetic fields or the material’s own magnetization. Magnetooptic effects are observed in both materials which emit light and materials which transmit (or reflect) light. The microscopic source of both types of effect is usually the energy level splitting induced by the magnetic field.1–5 Effects such as the Zeeman effect, which are observed in materials which emit light, have been of primary importance in deducing electronic structure and calculating energy levels. The emphasis in this chapter, however, is on materials in which magnetic fields generally alter some characteristic (such as intensity or state of polarization) of light which either propagates through the material or reflects off of its surface.
Solid Solution Design toward New Phosphor Discovery and Photoluminescence Tuning
Published in Ru-Shi Liu, Xiao-Jun Wang, Phosphor Handbook, 2022
Zhiqiang Ming, Ming Zhao, Zhiguo Xia
The 4fn energy-level splitting is mainly affected by the Coulomb field, spin-orbit coupling, and crystal field, and 5d energy-level splitting is mainly influenced by different matrix materials [14]. Compared with the 5d energy level, the 4fn energy level is extremely insensitive to lattice and the energy of the 4fn level can be regarded a constant in a host. Therefore, when studying the 4f–5d transitions of Eu2+ and Ce3+ ions, relevant factors affecting the 5d energy level need to be mainly considered. Figure 3.2 shows the effects of the host lattice on the 5d energy levels of free Eu2+ and Ce3+ ions. Based on the semiempirical Dorenbos model, the energy gap is strongly related to a given host lattice (A), which is dependent on the spectroscopic redshift D(A) and Stokes shift ΔS(A) [15]. If the first 5d energy level is known for a specific lanthanide ion in host A, one may determine the redshift D(A). From that, the positions of the unrelaxed and relaxed lowest 5d energy levels for all other lanthanides in the same compound can be predicted [16]. The D(A) is mainly determined by the centroid shift (εc) and crystal field splitting (εcfs). Several electrons of the anionic ligands move into the bare orbitals of the central metal ion and reduce the cationic valency, which would bring about the reduction of the interaction between metal ions and ligands. This effect is named the nephelauxetic effect (also known as the covalency effect). An increase in the degree of covalency effect can lead to a larger centroid shift, which means that the 5d levels of the free ion move to lower energy due to the decrease in the interelectron repulsion [17]. Besides the covalency of the chemical bonds between the luminescent center and its ligands, the polarizability of the neighboring anion ligands plays an essential role in the covalency effect. If anions or ionic complexes are put in, then the magnitude of centroid shift can be obtained according to the degree of the covalency effect. The extent of centroid shift is given in the following order: no ligands < F− < Cl− < Br− < I− < O2− < N3− < S2− < Se2− and SO42− < CO32− < PO43− < BO33− < SiO44− < AlO45−. In addition, the higher the degree of covalency, the larger centroid downshift will be generated, which reduces the emission energy of the 5d–4f transition.
First-principles study of point defects with different valences on the carrier activity, lifetime, absorption spectrum, and redox reaction of AlN (Li/Na/K) system
Published in Philosophical Magazine, 2022
Zhichao Wang, Qingyu Hou, Yuqin Guan, Zhenchao Xu, Chunwang Zhao
The calculated DOS of the all systems are shown in Appendix Fig. A3(a–g). Figure A3(a) shows that DOS of the Al36N36 system is symmetrical, proving that the Al36N36 system is non-magnetic. The magnetic moment is 0 μB. Figure A3(b–g) demonstrate that the Al34LiHiN36 (VAl2−,1−,0), Al34NaHiN36 (VAl2−,1−,0), Al34KHiN36 (VAl1−,0), Al35LiHiN35 (VN0), Al35NaHiN35 (VN0), and Al35KHiN35 (VN0) system DOS are asymmetrical, proving that the those doped systems are magnetic. This is because the cleavage of the impurity energy level leads to further magnetic moments in the system [60]. The magnetic moments of the doped systems are 0, 1, 1, 1 μB (μB is the Bohr magneton); 0, 1, 1, 1 μB; 0, 1, 1, 1 μB; 2, 0 μB; 2, 0 μB; and 1 and 0 μB, respectively. The energy level splitting caused by the built-in magnetic field will make the bandgap smaller [60]. The analysis result is the same as the band structure analysis.
Multireference configuration interaction calculations on the FeS molecule
Published in Molecular Physics, 2022
Ramon S. da Silva, Maikel Y. Ballester
According to Ref. [15], the calculation of the spin-orbit coupling A allows us to add a correction in the dissociation energy of the ground state. Taking this into account, we deduce a value of 26,809 cm, in fair agreement with the earlier studies. The energy level splitting of the ground state of FeS was examined using the ORCA program. The X state has spin components 4, 3, 2, 1, 0 with Ω = 4 attributed to the X-state (X) [8]. The computed energies of these components at R = 3.8218 a are 0.0, 206.7, 413.5, 620.0, and 826.6 cm for Ω = 4, 3, 2, 1, 0. These values are summarised in Figure 3 where the results derived for the ground state of FeO [82] at v = 0 are included just as reference. From the energetic point of view, the numerical values are in line showing the reliability of the theoretical data. Experimental studies are desirable to confirm these findings.
Quantum interference effect in plasmonic transmission in the presence of quantum emitters
Published in Journal of Modern Optics, 2022
Karun Mehta, Shubhrangshu Dasgupta
In this paper, we show how one can truly exploit the quantum interference effect to mimic the EIT in a plasmonic set up. In a three-level atomic system, the EIT is traditionally achieved by resonantly driving an atomic transition by a strong laser field (the control field). This control field creates two partially ‘dressed’ states. The amplitudes of transition to these states from a common ground state destructively interfere and give rise to transparency of a weak laser field (the probe field) [27]. In the plasmonic configuration, we use several interacting quantum emitters (QEs), all coupled to a common surface plasmon (SP) field, that exists along a plasmonic waveguide (PW). The coupling between these QEs leads to the transmission enhancement of the SP field. Our work is analogous to the EIT, as the guided SP field plays the role of the probe, while the coupling between the QEs leads to the necessary energy-level splitting, which is achieved by using a control field in case of atomic systems. Note that this is unlike PIT, in which it is the SP field that induces transparency of an external field.