Selected pair luminescence

In GaP, selected pair luminescence (SPL), whose principle is explained in Sect. 1.3.3, has been used by Street and Senske [163] to directly measure the transition energies of the MgGa, Znoa, and Cp acceptors. The advantage of this method is that a value of the ground state energy can also be obtained directly. The absorption by the classical method of a few lines of Be, Mg, Cd, and C acceptors in GaP has also been reported by Kopylov and Pikhtin [103]. 

The absorption of the G and D lines of the Znin acceptor in InP have been reported by Causley and Lewis [30], and this appears to be the only known acceptor absorption result for this compound. Their positions are 241.5 cm-1 (29.94 meV) for the G line (2P3/2 (Ts-) and 286.0 cm-1 (35.46 meV) for the D line (2P5/2 (Ts-). The scarcity of absorption results is due to the fact that such spectra would be close to the one-phonon absorption of InP (37.7 and 42.8meV for the TO and LO phonons, respectively). However, shallow acceptor transitions have been identified in InP by selective pair luminescence (SPL) and excitation spectroscopy (Dean et al. [48]). The separation from the IS3/2 ground state of some S and P acceptor states of Znin and Cdin have also been measured by Raman scattering [188]. 

Trigonal ML3 metal complexes exist as optically active pairs. The complexes can show enantiomeric selective binding to DNA and in excited state quenching.<34) One of the optically active enantiomers of RuLj complexes binds more strongly to chiral DNA than does the other enantiomer. In luminescence quenching of racemic mixtures of rare earth complexes, resolved ML3 complexes stereoselectively quench one of the rare earth species over the other. 35-39 Such chiral recognition promises to be a useful fundamental and practical tool in spectroscopy and biochemistry. 

Figure 9. (a) Schematic representation of the five-module format of a photoactive triad which is switchable only by the simultaneous presence of a pair of ions. This design involves the multiple application of the ideas in Figure 1. The four distinct situations are shown. Note that the presence of each guest ion in its selective receptor only suppresses that particular electron transfer path. The mutually exclusive selectivity of each receptor is symbolized by the different hole sizes. All electron transfer activity ceases when both guest ions have been received by the appropriate receptors. The case is an AND logic gate at the molecular scale. While this uses only two ionic inputs, the principle established here should be extensible to accommodate three inputs or more, (b) An example illustrating the principles of part (a) from an extension of the aminomethyl aromatic family. The case shown applies to the situation (iv) in part (a) where both receptors are occupied. It is only then that luminescence is switched "on". Protons and sodium ions are the relevant ionic inputs.

The observation of luminescence from laser dyes by ECL methods offers the possibility of using this approach to create dye lasers. A laser operating by ECL would not require an additional pump laser, and enhanced power, tunability, and wavelength selection are additional factors. While the pumping rate achieved by ECL previously has been two orders of magnitude lower than the optimal, Horiuchi et al. have reported a device structure designed to enhance the ECL efficiency and realize laser action driven by ECL [67], This experiment is illustrated in Fig. 14. A pair of sputter-deposited platinum film electrodes were positioned facing each other 2 to 7 microns apart. One electrode functioned... 

The reconciliation of these two apparently conflicting results is quite interesting and is connected to the broad distribution of recombination lifetimes. Those electron-hole pairs which are created with small separations are more likely to result in geminate recombination than the more distant pairs. The close pairs are also more likely to contribute to the luminescence and the distant pairs to LESR. Thus the two experiments are selectively measuring different parts of the distribution. The density of geminate pairs of separation, R, is given by. 

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