Temperature-dependent luminescence

Temperature-dependent luminescence measurements in the range from 77 to 300 K show quenching of the peak luminescence by a factor of about 15. Similar behavior is observed in the lifetime quenching [665, 666], As the band gap of the PECVD a-Si H is about 1.6 eV, nonradiative deexcitation of Er may occur at elevated temperatures. The amount of quenching lies in between that of c-Si and LPCVD a-Si H, just like the bandgap. 

FIGURE 44 Temperature-dependent luminescence and the corresponding luminescence decay of vanadate in (A) YPo.95Vo.o504 Eu NPs and (B) YV04 Eu NPs. Reprinted with permission from Riwotzki and Haase (2001). Copyright 2001 American Chemical Society. 

Ru(dmb)j(decb) ] , [Ru(decb) (dmb) ], and (Ru(decb) (dmb -4,4 -dimethyl-2,2 -pyridine, decb 4,4 -bis(ethylcarboxy)-2,2 -bipyridine). Emission properties of [Ru(bpy) nH O and the circular dichroism spectrum of the excited state absorption of (a)-[Ru(bpy)3] have both been reported. The luminescence of Ru(II) and Os(II) polypyridyls has been measured in MeCN as a function of pressure and temperature, and it has been found that at high pressures the radiative and non-radiative transition rates between the luminescent CT level and the ground state are generally increased by 5-10%. Temperature dependence luminescence studies on [Ru(bpy) L] ... 

Temperature-dependent luminescence spectra for a series of palla-dium(ii) and platinum(ii) complexes with thiocyanate, halide, and dithiocarbamate ligands have been investigated. The results show that the luminescence band maxima of palladium(ii) and platinum(ii) complexes have opposite shifts with increasing temperature. The palladium complexes exhibit a negative shift of at least 1 cm /K, while the platinum(ii) ones have a positive shift of -1-1.6 cm /K. ... 

A large amount of work has been published on Re complexes of the general type [(L)Re(CO)3(a-diimine)] +. These complexes exhibit Re —> (diimine) MLCT emission at room temperature in solution and the emission energy can be tuned by variation of the diimine, ancillary ligand, L, and solvent. Several reviews have appeared that discuss the luminescence behavior of these complexes. " Recently, detailed temperature-dependent luminescence measurements have been made on several methylated phenanthroline (w-phen) complexes of the type [ClRe(CO)3( i-phen)] the emission from the complexes was comprised of components from the MLCT and m-phen localized tt-tt states. Emission from this class of chromophores has been plied recently to immunoassays based on luminescence polarization of Re diimine complexes and the development of unique luminescent arylethynylene polymers. ... 

Grinberg M, Barzowska J, Shen YR, Bray KL, Hanuza J, Deareh PJ (2006) The effect of pressure on luminescence properties of Cr ions in LiSc(W04)2 crystals-Part II Pressure-and temperature-dependent luminescence kinetics. J Lumin 116 15... 

The temperature-dependent luminescence intensity of P-sialonrEu " is shown in Fig. 16.31. At 150 °C the luminescence of P-sialonrEu " remains 83 % of the initial... 

Trindade N, Tabata A, Scalvi R, Scalvi L (2011) Temperature dependent luminescence spectra of synthetic and natural alexandrite (BeAl204 Cr ). Mater Sci Appl 2 284-287 Trofimov A (1962) The nature of linear luminescence spectrum in zircon. Geochemistry 11 972-975 (in Russian)... 

Degen, J., Kupka, H., and Schmidtke, H.-H. (1987) Temperature-dependent luminescence spectra of [ReClt] doped in K2PtCl6-type crystals. Chem. Phys., 117, 163. 

Fig. 9. Temperatures dependence of the luminescence efficiency of the system Cai-jPbiWO for three values of X (modified from JA Groenink, thesis, Utrecht, 1979)...

The high-spin/low-spin interconverison in a Ni11 complex of the cyclam derivative (639) bearing a luminescent naphthalene substituent has been used as a fluorescent molecular thermometer.161 The Ni11 tends to quench fluorescence of the proximate naphthalene subunit, but the two spin states exert a different influence on the emission properties. Emission is temperature dependent, since the high spin —> low spin conversion is endothermic, i.e., a temperature increase favors formation of the low-spin form. 

The first photophysical investigation performed on stereochemically pure metal-based dendrimers having a metal complex as the core is that concerning the tetranuclear species based on a [Ru(tpphz)3]2+ core (tpphz=tetrapyrido[3,2-a 2, 3 -c 3",2"-h 2",3"j]phenazine) [67]. Dendrimer 45 is an example of this family. In this compound, two different types of MLCT excited states, coupled by a medium- and temperature-dependent photoinduced electron transfer, are responsible for the luminescence behavior. However, the properties of all the optical isomers of this family of compounds are very similar. This finding is also in... 

The temperature dependence of luminescence from the sample irradiated at 1 x 1013 cm-2 with 28Si+ indicates, above —110 K, an activation energy of 90 meV for the competing nonradiative recombination process— this competing process may be the thermal dissociation of geminate pairs or bound excitons at donorlike or acceptorlike centers. The 0.09-eV value of activation energy is consistent with the results of Troxell and Watkins (1979). 

Wallace WL, Bard AJ (1979) Electrogenerated chemi-luminescence. 35. Temperature-dependence of the ECL efficiency of Ru(bpy)32+ in acetonitrile and evidence for very high excited-state yields from electron-transfer reactions. J Phys Chem 83 1350-1357... 

Even when the d-d state is at much higher energy than the emitting level, it can still be of paramount importance in the photophysics and photochemistry of the system. Indeed, a major contributor to the temperature-dependent loss of emission intensity in luminescent metal complex based sensor materials is nonradiative decay via high-energy d-d excited states.(15) The model for this is shown in Figure 4.4A. The excited state lifetime is given by... 

There are possible advantages of the temperature dependence of excited state lifetimes. The dependence can be used for luminescence-based temperature sensors, which is an area of considerable interest. Clearly, with a suitable AE, complexes that give significant lifetime changes in a wide range of possible temperatures can be designed. We discuss this issue elsewhere.(16)... 

The temperature dependence of luminescent metal complexes can be controlled by molecular design that affects the energy gap between the emitting state and the deactivating d-d or by altering the preexponential factor for thermal deactivation. The sometimes large temperature dependencies of lifetime and quantum yields for metal complexes also suggest their use as temperature sensors. 

The long-lived phosphorescence of the tryptophan in alkaline phosphatase is unusual. Horie and Vanderkooi examined whether its phosphorescence could be detected in E. coli strains which are rich in alkaline phosphatase.(89) They observed phosphorescence at 20°C with a lifetime of 1.3 s, which is comparable to the lifetime of purified alkaline phosphatase (1.4 s). Long-lived luminescence was not observed from strains deficient in alkaline phosphatase. The temperature dependence of tryptophan phosphorescence in the living cells was slightly different from that for the purified enzyme, indicating an environmental effect. 

The mechanisms of luminescence decay from an optical center are of critical importance. In particular we have to know if there are any processes internal to the center or external to it, which reduce the luminescence efficiency. It is possible to define two decay times, ir, the true radiative decay time which a transition would have in absence of all non-radiative processes, and r, the actual observed decay time, which maybe temperature dependent, as will usually occur when there are internal non-radiative channels, and which may also be specimen dependent, as when there is energy transfer to other impurities in the mineral. The quantum yield may be close to unity if the radiationless decay rate is much smaller than the radiative decay. 

The luminescence of Bi " is quite diverse and depends strongly on the host lattice (Boulon 1987 Blasse and Grabmaier 1994 Blasse et al 1994). For the heavy Bi " the transitions between the ground state and the Pi state becomes additionally allowed by spin-orbit mixing of the Pi and Pi states. After excitation at low temperature, the system relaxes to the lowest excited state. Consequently, the emission at low temperatures can be ascribed to the forbidden transition Pq- Sq and has a long decay time. Nevertheless, both Pi and Po are emitting levels and they are very close so that at higher temperatures the luminescence from the Pi level may appear with a similar spectrum, but shorter decay (Fig. 5.49). 

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