Potential well

About: Potential well is a research topic. Over the lifetime, 1430 publications have been published within this topic receiving 30812 citations.

Temperature dependence of photoluminescence in silicon quantum dots

Abstract: The optical properties of silicon quantum dots (QDs) embedded in a SiO2 matrix are investigated at various temperatures using photoluminescence (PL) and time-resolved photoluminescence. Two broad luminescence bands, the S-band located at 600–850 nm and the F-band located at 450–600 nm, are observed. In the S-band a stretched exponential time evolution is observed and the short wavelengths have significantly shorter lifetimes than the long wavelengths. In the low temperature regime, the process of carrier delocalization from the defect states and capture into the QDs is dominant, which results in a decrease in PL intensity from the F-band and an increase from the S-band. In the high temperature regime, the carriers captured into the QDs decrease due to competition between the defect states, which results in a PL intensity decrease for both bands. The PL intensity on the high energy side of the S-band decreases more strongly than that on the low energy side due to the state filling effect, which results in a 30 nm red shift. The S-band is attributed mainly to zero-phonon electron–hole recombination due to enhancement of the quantum confinement effect. The F-band has a single exponential evolution with a much shorter lifetime of nanoseconds and is attributed to defect states of silicon oxide.

Efficient infrared-upconversion luminescence in porous silicon: A quantum-confinement-induced effect.

Abstract: We demonstrate for the first time that a porous silicon layer (PSL), which has a bright light-emission band in the range of 500--700 nm, exhibits a strong visible-range luminescence under the illumination of an infrared ultrashort pulsed laser. The dependence of integrated luminescence intensity on pump power shows that this is a third-order nonlinear optical effect. By comparing with UV-light-excited spectra of PSL and samples with low porosity which have inefficient luminescence, a possible explanation is proposed whereby the large nonlinear optical response is due to the quantum confinement effect.

Tuning the potentials of "extra" electrons in colloidal n-type ZnO nanocrystals via Mg2+ substitution.

Abstract: Colloidal reduced ZnO nanocrystals are potent reductants for one-electron or multielectron redox chemistry, with reduction potentials tunable via the quantum confinement effect. Other methods for tuning the redox potentials of these unusual reagents are desired. Here, we describe synthesis and characterization of a series of colloidal Zn(1-x)Mg(x)O and Zn(0.98-x)Mg(x)Mn(0.02)O nanocrystals in which Mg(2+) substitution is used to tune the nanocrystal reduction potential. The effect of Mg(2+) doping on the band-edge potentials of ZnO was investigated using electronic absorption, photoluminescence, and magnetic circular dichroism spectroscopies. Mg(2+) incorporation widens the ZnO gap by raising the conduction-band potential and lowering the valence-band potential at a ratio of 0.68:0.32. Mg(2+) substitution is far more effective than Zn(2+) removal in raising the conduction-band potential and allows better reductants to be prepared from Zn(1-x)Mg(x)O nanocrystals than can be achieved via quantum confinement of ZnO nanocrystals. The increased conduction-band potentials of Zn(1-x)Mg(x)O nanocrystals compared to ZnO nanocrystals are confirmed by demonstration of spontaneous electron transfer from n-type Zn(1-x)Mg(x)O nanocrystals to smaller (more strongly quantum confined) ZnO nanocrystals.