Band size-tunable

Structures made by electrochemical nanostructuring of semiconductors show photonic band gap tunable with the period of structure, nanostmcture sizes and their dielectric surroundings. Experiments demonstrate both phase matching for second-harmonic generation and an enhancement of second- and third-harmonic generation efficiencies in the nanostructured materials. 

Systematic size induced changes in the electronic structure of QDs have been extensively studied in the last decade. Sustained efforts have established interesting applications based on the blue-shift of the absorption edge due to the quantum confinement in nanometer-sized samples. Absorption spectroscopy is one of the simplest technique that has been employed to study the electronic structure of nanocrystals. Upon irradiation with light of energy greater than the band gap, NCs are known to absorb photons and promote electrons from the valence band (VB) to the conduction band (CB). The onset of the absorption spectrum generally corresponds to the band gap of QDs. The band gap is size tunable and decreases very sensitively with increase in the size of the dot. This relationship is shown in Fig. 2a for a typical system like the ZnO QDs. This size dependence... 

Tunable diode laser absorption spectroscopy (TDLAS) has been used to measure oxides of nitrogen during flight (71). By tuning the laser to specific infrared absorption bands, the technique can selectively measure each compound. Detection limits are higher (25-100 pptrv for a 3-min response time) than the best chemiluminescent methods, and the instrumentation is less amenable to aircraft operations than the chemiluminescence techniques because of weight and size. 

Tunable narrow-band lasers can be tuned to every wanted molecular transition 10 I A within the tuning range of the laser. However, selective excitation of a single upper level can only be achieved if neighboring absorption lines do not overlap within their Doppler width (Fig. 1.53). In the case of atoms this can generally be achieved, whereas for molecules with complex absorption spectra, many absorption lines often overlap. In this latter case the laser simultaneously excites several upper levels, which are not necessarily energetically close to each other (Fig. 1.53a). In many cases, however, the fluorescence spectra of these levels can readily be separated by a spectrometer of medium size [160]. 

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