The indirect band gap of icosahedral B12As2 (IBA) has been determined by variable temperature photoluminescence measurements (8 K-294 K) on solution-grown bulk samples. In addition, evidence of three shallow acceptor levels and one shallow donor level is reported. The low-temperature spectra were characterized by broad and intense deep defect emission, donor-acceptor pair (DAP) bands, and exciton recombination. The appearance of DAP emission verifies the incorporation of a donor in IBA, which has not been reported previously. The temperature dependence of the free exciton (FE) intensity reflected a FE binding energy of 45 meV. The variation of the FE peak position with temperature was fitted with both Varshni and Passler models to determine an expression for the temperature dependence of the indirect band gap. The resulting low and room temperature band gaps are Eg(0) = 3.470 eV and Eg(294 K) = 3.373 eV, respectively. The latter is not consistent with previous reports of the room temperature band gap, 3.2...

/pdf/photoluminescence-investigation-of-the-indirect-band-gap-and-4n9rx8rhhc.pdf

Photoluminescence investigation of the indirect band gap and shallow impurities in icosahedral B12As2

We report the results of the investigation of the temperature dependence of the spontaneous emission of localized excitons in Zn1−xCdxSe quantum wells (QWs). Two main peaks, which show a strong change in relative intensities with temperature, dominate the spectra. The presence in the spectra of biexcitons and bound excitons was ruled out after the corresponding analyses. Calculation of the fundamental transitions of the QWs suggested that the peaks are due to thickness fluctuations of one and two monomolecular layers. The successful analysis of the spectra in terms of a simple two-level model indicated that localization of excitons due to QW thickness fluctuations and exciton migration are basic processes which have noticeable influence in the spontaneous emission of Zn1−xCdxSe QWs.

Temperature dependence of exciton localization in Zn1−xCdxSe quantum wells

Luminescence as a weak cold glow from rotting wood, certain insects, mushrooms, fish, microorganisms, sea algae, minerals, and, finally, polar lights has been known since ancient times. This interesting and initially mysterious phenomenon attracted the attention of many scientists during the last four centuries (Harvey, 1957). However, it was not subjected to systematic study until the middle of the 19th century. Stokes (1852) formulated the first law in the history of luminescence (Stokes’ rule), which states that the wavelength of the luminescence is greater than the wavelength of the exciting radiation.

Theory of Luminescence

Photoluminescence properties of intra-well exciton migration in Zn1−xCdxSe quantum wells

Free exciton and bound exciton photoluminescence (PL) of a quantum well (QW) in the presence of free carriers is studied in a model that includes the transfer of particles among free carrier, free exciton, and bound exciton states under an external excitation It is shown that the free carrier state is important not only at high temperature but also at low temperature General formulas for the free exciton, bound exciton, and free carrier PL are developed The two‐dimensional (2D) law of mass action for the free carrier and free exciton PL is reproduced at high temperature, and the model of the free exciton trapped by the impurities is obtained for the QW system with low defect concentration Free exciton and bound exciton PL for high defect concentration is also discussed and the 2D law of mass action is obtained at high temperature as well Experimental observations such as the thermal behavior of free exciton and bound exciton PL, the recently observed sharp temperature‐induced reduction of the PL line

Free carrier, free, and bound exciton photoluminescence of quantum well

Free exciton (FE) and bound exciton (BE) photoluminescence (PL) of quantum well (QW) affected by free carrier (FC) is studied by a model which includes the transfer of particles among FC, FE, and BE states. It is shown that FC state is important not only at high temperature but also at low temperature. General formulas for FE and BE PL are developed. The two‐dimensional law of mass action is reproduced for high temperature, and the trapping of FE by defects is obtained for low defect concentration. Temperature behavior of FE and BE PL for high defect concentration is also discussed.

Er‐Xuan Ping

Papers

Free and bound exciton photoluminescence of quantum well affected by free carriers