Relaxation emission lifetime

Whether a complex in an excited state can manifest its enhanced redox properties will depend on whether it can undergo electron transfer faster than it undergoes something else, such as relaxation to the ground slate (luminescence). The emission lifetime of t Ru(bpy)j]2 in aqueous solution at 25 °C is 0.6 /us and it increases... 

Mc/s and the spontaneous emission lifetime is 10 sec. Obviously this lifetime is too long and the transitions will be saturated exceedingly easily. In other words, the populations of the two levels become essentially equal and no net transition can be observed. Fortunately there are a number of nonradiative relaxation mechanisms open to the upper spin level including interactions with other electrons, with nuclei having nuclear magnetic moments, and with the lattice. The latter process is often known as spin-lattice relaxation. The term "lattice" generally refers to the degrees of freedom of the system other than those directly related with spin. Spin... 

Further quantum yield measurements (111) and emission lifetimes (111-113,115) have also been reported which demonstrate that the radiative transition probability from a vibronic state is determined by the combination of vibrational modes that have been excited. The transition rates that may be of interest in comparing data from all three phases are, of course, those from the lower levels of Sj, since relaxation in higher-pressure gases and condensed media will lead to these states. The data of Spears and Rice (111) show that the emission probability from the levels 0, 6 16 and 1 are 2.2 x lO s", 3.4 x 10 s l,... 

Intraband relaxation in most systems occurs on timescales that are short relative to the spontaneous emission lifetimes of the intraband transition, and this has hindered potential applications of intraband transitions for infrared detection and emission. Quantum dots with large number of surface traps have however been shown to rapidly extract electrons from the P levels of the nanocrystal. Mid infrared photons incident on such a material induce a PL quench at room temperatures, allowing for the visualization of mid-infrared light. 

Due to the simple electronic stmcture of Yb ", Yb -doped ceramic lasers have no problem of de-excitation processes like the concentration-dependent selfquenching by downconversion or upconversion cross-relaxation. However, a reduction in emission lifetime and emission quantum efficiency has been observed. In addition, cooperative processes could occur, due to the interaction between two excited Yb " ions, when the concentrations of Yb " are too high. The parasitic deexcitation processes are usually accompanied by the generation of heat that is up to twice as much as that due to the quantum defect [202]. Therefore, it is important to have a good matching between the pump and mode volume in the laser materials. 

In photochemical experiments we are generally concerned with the spontaneous luminescence of the excited molecule simultaneous with the deactivation of the molecule to the ground electronic state. The study of parameters relating to luminescence (the energy distribution of emitted light, generally known as the emission spectrum, the emission lifetimes and the frequency of incident light needed to observe emission) provide important information on the excited state relaxation processes. ... 

The radiative and nonradiative (fc ) rate constants estimated using the emission lifetimes (Tobs) and the intrinsic emission quantum yields ( Ln) are summarized in Table 6.1. The radiative rate constant for Eu(hfa)3(fBu-xantpo) in acetone was estimated to be 5.4 x 10 s This value is much similar to that for Eu(hfa)3(fBu-xantpo) in acetone-t/e (5.5 x 10 s ). The nonradiative rate constant for Eu(hfa)3(fBu-xantpo) in acetone-t/s (2.7 x 10 s ) is smaller than that for Eu(hfa)3(fBu-xantpo) in acetone (3.0 x 10 s ). The relatively smaller kai for Eu(hfa)3(fBu-xantpo) in acetone-t/s is attributed to the suppression of vibrational relaxation surroundings of the Eu(Ill) complex. The nonradiative transitions of lanthanide complexes are affected by the high-vibrational frequency of C-H and O-H bonds of solvent. The author consider that introduction of deuterated solvent is effective for enhancement of emission quantum yield of octa-coordinated Eu(lll) complexes. 

Fig. 15. Energy level diagram fisr the three lowest excited states of [Ru(bpy-hg)j] in (Zn(bpy-hglgKClOJz.The spin-latice relaxations (sir) from state 111) to the states II) and 11) are very fast,but the relaxation from state II) to 11) is hindered at T = 1.2 K, due to a slow process of direct phonon emission. This leads to a decay time of 220 10 ns [165,166], while the emission from state 11) decays with the usual emission lifetime of t, = 230 ps. Since the states II) and 11) are deactivated differendy by Franck-Condon (FC) and Herzberg-Teller (HT) vibrations, respectively, the emission spectra change distincdy with time (see Fig. 16). Similar properties are also observed for partially and per-deuterated [Rulbpylg] chromophores...

The lifetime of an analyte in the excited state. A, is short typically 10 -10 s for electronic excited states and 10 s for vibrational excited states. Relaxation occurs through collisions between A and other species in the sample, by photochemical reactions, and by the emission of photons. In the first process, which is called vibrational deactivation, or nonradiative relaxation, the excess energy is released as heat thus... 

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