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3 Nanoparticles
Published in Odireleng Martin Ntwaeaborwa, Luminescent Nanomaterials, 2022
S.J. Mofokeng, F.V. Molefe, L.L. Noto, M.S. Dhlamini
Metal oxide semiconductors as luminescent materials are mostly designed and used as a host lattice that is doped with a (RE3+) ion, which acts as the luminescence centers [11–14]. The role of a suitable host materials is to tune the luminescent lifetime for the luminescent materials that consist of intrinsic defects. These defects are known to trap and release the electrons to the luminescent centres, which result in extended duration of the emission that can last up to several hours or days. The host is the one that determines whether the f-f transition or the f-d transition of the dopant ion will be favoured, including the intensity of their signal [11]. Recently, researchers are working hard to develop different host materials that can produce high quantum yield. Some materials include mixed luminescent materials, doped luminescent materials and co-doped luminescent materials [12].
Time-Resolved Laser-Induced Fluorescence Spectroscopy for Staging Atherosclerotic Lesions
Published in Mary-Ann Mycek, Brian W. Pogue, Handbook of Biomedical Fluorescence, 2003
Laura Marcu, Warren S. Grundfest, Michael C. Fishbein
The most important characteristics of a fluorophore (fluorescent molecule) for fluorescence measurements are the quantum yield and fluorescence lifetime. The quantum yield is expressed as the ratio of the number of photons emitted to the number of photons absorbed. The fluorescence, or radiative, lifetime is determined by the time the molecule spends in the excited state prior to decaying radiatively to the ground state. Direct measurements of fluorescence lifetime, τ, is based on the assumption that this process follows first-order kinetics quantitatively described by equation: It=I0e−t/τ
Molecular Fluorescence and Phosphorescence
Published in Grinberg Nelu, Rodriguez Sonia, Ewing’s Analytical Instrumentation Handbook, Fourth Edition, 2019
Ricardo Q. Aucelio, Sarzamin Khan, Andrea R. da Silva, Fernando M. Lanças, Emanuel Carrilho
Because of the lower relative energy of the excited triplet state, the phosphorescence emission band of a substance always occurs at higher wavelengths (less relative energy transition involved) than fluorescence, as illustrated in Figure 6.2 for benzo[f]quinolone (intensity normalized spectra). In contrast, because of the chain of events, fluorescence lifetimes are orders of magnitude shorter than the ones of phosphorescence and the probabilities of these processes occurring are reflected on their quantum yield values. In most cases, fluorescence quantum yield (ϕF) is significantly higher than phosphorescence quantum yields (ϕP) unless conditions for the occurrence of phosphorescence are extremely favorable.
Organo-soluble dendritic zinc phthalocyanine: photoluminescence and fluorescence properties
Published in Inorganic and Nano-Metal Chemistry, 2022
Ebru Yabaş, Safacan Kölemen, Emre Biçer, Toghrul Almammadov, Pınar Başer, Mehmet Kul
On the other hand, fluorescence quantum yield is a measure of the efficiency of converting absorbed light into emitted light and is a parameter that can be used to explain energy transfer within the molecule.[60] The fluorescence properties of 1 and 2 in solution phase were examined and Figure 5 shows the emission and excitation spectra for 1 and 2. The excitation and the absorption spectra of 1 and 2 are similar in DMSO, and these spectra are mirror images in the emission spectra.[61] Fluorescence quantum yields were calculated from measured emission spectra of compounds. Fluorescence quantum yields for compound 1 and 2 were found to be 0.26 (26%) and 0.33 (33%) respectively (Table 1). The fluorescence quantum yields of compounds 1 and 2 are higher than the fluorescence quantum yields of unsubstituted ZnPc. At the same time, it was observed that fluorescence quantum yield increased with increasing generation in dendritic phthalocyanines. As a result, the substituents attached to the phthalocyanine ring have a significant effect on the fluorescence quantum yield.[62] The energy transfers between the phthalocyanine ring and the substituted groups may have resulted in an increase in fluorescent quantum efficiency.[60]
Effect of operating conditions and interfering substances on photochemical degradation of a cationic surfactant
Published in Environmental Technology, 2018
Bijoli Mondal, Asok Adak, Pallab Datta
In addition to determination of rate constant, quantum yields were also calculated for the degradation of CTAB by UV irradiation. The quantum yield is useful for determination of the photolytic efficiency and is defined as the moles of a compound transformed per mole of photons absorbed by the compound [25]. The apparent fluence-based pseudo-first-order rate constant was used to calculate the apparent quantum yield (Equation (2)):In Equation (2), is the experimentally determined apparent fluence-based pseudo-first-order photolysis rate constant (cm2 mJ−1), is the apparent quantum yield at 253.7 nm (mol/Einstein), is the apparent molar absorptivity at 253.7 nm (M−1 cm−1) and is the molar photon energy at 253.7 nm (4.72 × 105 J/Einstein). The apparent quantum yield for degradation of CTAB was found to be 0.305 (± 0.043) mol/Einstein. Comparable quantum yields of 0.582 and 1.344 mol/Einstein for CTAB and linear alkylbenzenesulfonate were reported as in previous studies [26,27].
Phthalocyanines formed from several precursors: synthesis, characterization, and comparative fluorescence and quinone quenching
Published in Journal of Coordination Chemistry, 2018
H. R. Pekbelgin Karaoğlu, H. Yasemin Yenilmez, Makbule B. Koçak
Fluorescence lifetime (τF) is the average time of the molecule at the excited state before fluorescing. This value affects the quantum yield, and longer lifetime results in a higher quantum yield of fluorescence. Factors, such as internal conversion and intersystem crossing, reduce the fluorescence lifetime while the value of ΦF decreases. In the present examination, fluorescent lifetimes (τF) were calculated by the equation of Strickler and Berg. [37]. Using this equation, we obtained a good correlation between fluorescent lifetimes, both experimentally and theoretically, of the unaggregated molecules, which was also the case for the octa-(3-(diethylamino)phenoxy- and hexylsulfanyl-substituted Pc compounds in DMF. The fluorescence lifetimes (τF) and natural radiative lifetimes (τ0) of ZnPc were calculated by the respective equation, and the corresponding values are displayed in Table 2. The lifetimes of fluorescence (τF) values of the octakis(3-(diethylamino)phenoxy and hexylsulfanyl-substituted zinc phthalocyanine are lower than that of unsubstituted zinc phthalocyanine in DMF [38]. The kF value of the substituted zinc phthalocyanines was smaller than that of unsubstituted ZnPc [23].