Luminescent loss mechanisms

Tummeltshammer, C., Brown, M.S., Taylor, A., Kenyon, A.J., and Papakonstantinou, I. (2013) Efficiency and loss mechanisms of plasmonic luminescent solar concentrators. Opt Express, 21 (S5), A735-A749. 

To investigate materials such as laser gain media only simple experimental techniques are usually required. To evaluate the potential of a new material in a technological application it is often sufficient to measure absorption and emission spectra along with luminescence lifetimes, though it is desirable to also have an indication of relevant loss mechanisms. These include nonradiative decay, excited state absorption and energy transfer. The result of significant nonradiative decay is indicated by variations in luminescence intensity and lifetime as a function of temperature... 

Negative Ions and Trapped Electrons. At the present time we can only speculate on the nature of electron traps in irradiated polyethylene. Partridge (33) suggests that electrons are trapped between molecular chains because luminescence in irradiated polyethylene occurs in the temperature intervals where mechanical losses occur. For large doses, free radicals, R , are abundant enough to be significant in trapping electrons. The reaction ... 

Interactions between luminescent ions cause nonradiative losses by two mechanisms energy migration and crossrelaxation. 

The rate constant for total deactivation of singlet oxygen by Vaska s Complex + kq) was determined by IO2 luminescence quenching and is listed in Table 1. In order to obtain the rate constant of chemical quenching (k ), competition experiments were carried out with 9,10-dimethylanthracene (DMA, same conditions as above). DMA is known to quench IO2 only chemically. " Loss of 1 and DMA were monitored spectrophoto-metrically and the results fitted to the equation of Higgins et al A second independent determination of was obtained by measurements of direct disappearance of 1 compared with a tetramethylethylene (TME) reference, which quenches singlet oxygen only by a chemical mechanism. Values of / r, and by difference, of kq, are listed in Table 1,... 

In the majority of cases the compatibility of the polymers is characterized by the glass-transition temperature Tg, determined by methods such as dilatometry, differential scanning calorimetry (DSC), reversed-phase gas chromatography (RGC), radiation thermal luminescence (RTL), dynamic mechanical spectroscopy (DMS), nuclear magnetic resonance (NMR), or dielectric loss. The existence of two... 

Laser emission efficiency has a strong dependence on the distribution of the de-excitation processes. It has been proved that proper management of the pump and laser mode volumes is crucial to achieve high CW laser efficiency, reduce the parasitic luminescence, and decrease the heat generation, which can result in the loss of excitation by ASE, distortion of the beam, and mechanical fracture. These properties are also important for the design of cooling systems and evaluation of material characteristics, e.g., emission quantum efficiency from thermal lensing data [1, 11]. 

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