Quantum size effect, inorganic

The optical properties of nanoparticles are known to be significantly different from their corresponding bulk materials. The size effect of these NPs causes special optical responses such as surface plasmon resonances (SPRs) in metal nanoparticles or quantum size effects in semiconductors. The possibility of confining these NPs in inorganic matrices produces new functional materials with collective and novel properties. 

The effective mass of electron or hole is defined as h2 l d2E k) / dk2. Near the bottom of the band where the E k) versus k curve is close to parabolic, the effective mass (m ) is + P2)IPiP2a2- Therefore, the curvature of the band and the effective mass of the electron or hole are determined by p. With large p (in a strongly interacting system such as inorganic semiconductors), the curvature of the band is steep, the electron or hole effective mass is small, and the bandwidth is large a more pronounced quantum size... 

Microcrystals of some diacetylenes, prepared by the reprecipitation method, have been studied as dispersions in liquid media. Interesting behavior has been observed in the solid-state polymerization of diacetylene monomers and with the optical properties of polydiacetylene (PDA) microcrystals. First, the polymerization perfectly proceeded from one end to the other end of the diacetylene microcrystals. Next, the excitonic absorption peak position was found to shift to higher energy side with decreasing size of the PDA microcrystals. The size effect was observed even for crystals as large as 100 nm or more in contrast to conventional quantum effect of inorganic semiconductors where size effect is observed only for microciystals of less than about 10 nm size. In addition, since the microcrystal dispersions in water have low optical loss, the c tical Kerr shutter response of PDA microciystals could be measured, and the non-resonant value was estimated to be on the order of 10 to 10" esu in very low concentrations (ca. 10 M). 

---