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Photonic Nanodevices and Technologies against Light Pollution
Published in Tuan Anh Nguyen, Ram K. Gupta, Nanotechnology for Light Pollution Reduction, 2023
Elisangela Pacheco da Silva, Elizângela Hafemann Fragal, Ederson Dias Pereira Duarte, Sidney A. Lourenço, Edvani C. Muniz, Thiago Sequinel, Rafael Silva, Eduardo José de Arruda, Vanessa Hafemann Fragal
LED is an electronic device that emits light through solid, semiconductor material such as gallium arsenide (GaAs) or gallium phosphide (GaP), with positive and negative polarities when energized by an electrical current. Figure 13.5a illustrates the basic LED conformation. LED is a semiconductor diode of the type P-N junction, which, when energized, emits visible light – hence LED (Light-Emitting Diode). Light is not monochromatic but consists of a relatively narrow spectral band produced by the electron’s energetic interactions. The light-emitting process by applying an electrical source of energy is called electroluminescence. At any forward-biased P-N junction, within the structure, close to the junction, hole and electron recombination occurs. This recombination requires the energy possessed by the electrons to be released, which occurs in the form of heat or photons of light Figure 13.5b [23].
Light Sources
Published in Toru Yoshizawa, Handbook of Optical Metrology, 2015
Electroluminescence is the light emission when electric field is applied to a material. Electro-luminescence in semiconductors results from radiative recombination of electrons from the conduction band with holes from the valence band. Prior to recombination, electrons and holes are separated either by doping of the material to form a p−n junction (as in electroluminescence devices such as LEDs) or through excitation by impact of high-energy electrons accelerated by a strong electric field. When the emission is triggered by an electric current injected into a forward-biased p−n junction, as in the case of LEDs, the process is called injection electroluminescence [65,66]. Examples of electroluminescent materials include III–V semiconductors, such as InP, GaAs, and GaN, powder zinc sulfide doped with copper or silver, thin-film (TF) zinc sulfide doped with manganese, organic semiconductors, natural blue diamond (diamond with boron as a dopant), etc. In crystals such as diamonds, the source of luminescence can be lattice defects.
MOF-based Electrochemical Sensors for Nitrogen Oxide/Carbon Dioxide
Published in Ram K. Gupta, Tahir Rasheed, Tuan Anh Nguyen, Muhammad Bilal, Metal-Organic Frameworks-Based Hybrid Materials for Environmental Sensing and Monitoring, 2022
Raghabendra Samantaray, Soujanya Ghosh, Nityananda Agasti
Another class of MOFs, called electroluminescent MOFs, have been investigated in the development of electroluminescent sensors. These cells are the simplest type of electroluminescent devices, consisting of a thin layer of conjugated polymer placed between two electrodes [42]. Electroluminescent devices can emit light by applying an electrical current or a strong electric field as electrical energy is converted into visible radiation. It is known that electroluminescent devices can be fabricated by using either organic or inorganic electroluminescent materials. MOFs are an organic-inorganic hybrid system that could form attractive electroluminescent materials with the overall advantages of both [42].
A series of theoretical studies on phosphorescent materials based on deep red/near-infrared iridium complex with low-efficiency roll-off performance
Published in Molecular Physics, 2023
Ye Ji, Xi-Lian Guo, Jia-Yu Yang, Hai-Han Zhang, Xu-Hui Liu, Ming-Xing Song, Zheng-Kun Qin, Jia Wang, Fu-Quan Bai
The efficiency of OLED devices depends on the injection, transport and balance of electron and exciton compounding. Table 2 shows the ionisation potentials (IPs), electron affinities (EAs), hole recovery potential (HEP), electron recovery potential (EEP), ‘small pole’ stability energy (SPE) and recombination energy λ of these six complexes. IPs and EAs are used to predict holes and barriers to electron injection as well as to predict charge transfer rate and equilibrium. For electroluminescent phosphors, the lower IP means that the holes enter more easily into the light-emitting layer of the hole transport layer (HTL); the higher EA indicates that electrons are more easily introduced into the electron transport layer (ETL). Many reports have confirmed trends in comparing IPs and EAs to speculate on charge injection features. In the ‘small pole’ stability energy, the same thing was found by us. At the same time, the self-grasping charge energy is what we are speculating in this SPE-based material. The redundant electrons trapped by geometric relaxation also lead to the SPE.
Theoretical study on a series of Blue-Green Ir(III) complexes used in OLED
Published in Molecular Physics, 2023
Hao-Yuan Chi, Guo-Qing Xi, Xue-Ming Zhao, Shao-Jun Qu, Xiang Liu, Ye Ji, Ming-Xing Song, Yong-Ling Zhang, Zheng-Kun Qin, Hong-Jie Zhang
The efficiency of OLED devices depends on the injection, transport, and balance of electrons and exciton compounding. The IPs, EAs, λ, EEP, SPE, and HEP are listed in Table 2. Here, IPs are ionisation potentials, EAs are electron affinities, λ is reorganisation energies, EEP is electron-extraction potential, SPE is stabilisation energy, and HEP is hole-extraction potential [8]. The ionisation potentials and electron affinity values can estimate the potential barriers for holes and electrons. Recombination energy was assessed for equilibrium and charge transfer rates. In electroluminescent materials, a lower electron affinity implies that it is more difficult to enter from the electron-transport layer (ETL). Higher ionisation energy makes it more difficult to enter the hole-transport layer (HTL) [9]. We did not consider the solvent factor because it is negligible [31–35].
Theoretical research on the relationships between aromatic ligands and spectroscopic properties of Pt(II) complexes
Published in Molecular Physics, 2022
In summary, a series of cyclometalated Pt(II) complexes have been explored with theoretical calculation methods. According to the calculations, the minimum values and maximum values of ESP are all elevated with the –CF3 introduced, which implies the electrons are transferred to the electron withdrawing group. All the S1 excitations are local excitation (LE) and mainly arose from pyrazolate ligand, metal to pyridyl and pyrimidinyl ligand. With respect to fluorescent emissions, complex 3 represents distinctive characteristics. For complex 3, most of the holes and electrons are located in the centered metal ion, so this excitation should be assigned as MC rather than MLCT and LLCT of the other three complexes. The electroluminescent properties calculation shows that complex 1 is suitable for hole transport material and complex 4 can be applied to electron transport material. Complexes 2 and 4 have stronger molecular rigidity and little structural distortions between different states. Complex 3 shows significant structural distortions on the S1 state and it may be applied in TADF materials.