The dependence of band-structure parameters, in particular the effective masses of electrons, heavy, and light holes, on hydrostatic pressure has been determined in ZnSe by two-photon magnetoabsorption. The electron mass and the average hole masses are found to he pressure-independent, whereas the valence-band warping increases with pressure.

The pressure shift of S excitons in the rutile-type semiconductor tin oxide (SnO(2)) is measured by two-photon absorption. From these data the pressure coefficients of the band gap (62.0 meV/GPa) and of the exciton binding energy (0.87 meV/GPa) are determined. (C) 1999 Elsevier Science Ltd. All rights reserved.

At hydrostatic pressures up to 12 GPa, photoluminescence experiments were performed simultaneously on zincblende (cubic) and wurtzite (hexagonal) gallium nitride. The linear band gap pressure coefficient of hexagonal GaN was determined to be (0.94 +/- 0.04) meV/GPa larger than the one of cubic GaN.

First results are presented on two-photon magnetoabsorption under hydrostatic pressure in ZnSe. The lifting of the 24-fold degeneracy of P excitons, which are only accessible by two-photon transitions by a magnetic field allows the determination of a large number of band-structure parameters, among them electron and hole masses and g-factors.

The S exciton series belonging to the fundamental gap and two hitherto unknown valence bands with even parity have been discovered by two-photon spectroscopy in the rutile-type semiconductor tin oxide (SnO2). Since at least three excitons were observed for each band, it was possible to determine accurately exciton binding energies and band gaps.

Photoluminescence and two-photon measurements were performed on hexagonal bulk GaN. From photoluminescence we have obtained the energies of free 1S excitons, from two-photon spectroscopy the energies of 2P excitons. These results together allow an accurate determination of exciton binding energies and band gaps

Low-temperature photoluminescence measurements are performed simultaneously on cubic (zinc blende) and hexagonal (wurtzite) gallium nitride at hydrostatic pressures up to 11.9 GPa. The linear pressure coefficient of the band gap of hexagonal GaN is found to be (0.94±0.04) meV/GPa larger than that of cubic GaN.

We have investigated the effects of isotopic composition on the band gap of CuCl on a series of samples made out of the stable isotopes (CU)-C-63, (CU)-C-65, Cl-35, and Cl-37. Besides specimens containing elements with the natural abundances, we have measured samples with monoisotopic sublattices as well as artificial mixtures of isotopes. With nonlinear (two-photon absorption, second-harmonic generation) and linear (luminescence) optical spectroscopy we find that the fundamental gap of CuCl increases by 364(18) mu eV/amu when increasing the Cl mass. However, it decreases by 76(5) mu eV/amu when increasing the Cu mass. Using a two-oscillator model for the lattice dynamics of CuCl we show that these rates are consistent with the anomalous increase of the band gap with increasing temperature. These effects can be traced back to the strong p-d mixing in the copper halides. From the temperature dependence of the band gap of CuBr we also estimate the changes of its gap with isotopic composition.

Strontium reacts with nitrogen and hydrogen resp. deuterium under well defined conditions to a phase containing hydride, imide and nitride ions.Sr is evaporated at 1000 degrees C. The Sr vapor reacts with N-2 and H-2 resp. D-2 (p(N-2) = p(H-2/D-2) = 50 mbar) in the gas phase. The product crystallizes as orange-yellow resp. black needles at 800 degrees C.Neither X-ray single crystal nor X-ray and neutron powder diffraction data led to an acceptable model for the crystal structure. A high resolution diffraction experiment with synchrotron radiation gave the needed informations:Splitting of reflections led to a model in R3m with a = 3.870(1) Angstrom and c = 18.958(3) Angstrom. Further split reflections indicate, that the crystals contain areas where SrNH is a second phase besides Sr-2(PI)N. Neutron diffraction data (measured at 2 K, 10 K, 300 K and 505 K) were interpreted by a two phase model with Sr-2(D)N/SrND: In a slightly distorted cubic close packing of Sr-atoms hydride and nitride resp. imide ions occupy each by one third octahedral sites fully and in an ordered way.

The direct observation of free A, B, and C excitons with n=2 in hexagonal bulk gallium nitride (GaN) by two-photon spectroscopy is reported. From these data, the band gaps, exciton binding energies, and hole masses for the three uppermost valence bands are calculated.

Two-photon spectroscopy allows to observe unambigously the free A, B, and C excitons with n=2 in bulk GaN. Their energies allow the precise determination of the three band gaps and of the exciton binding energies.

Two-photon absorption at low temperatures was used to determine the pressure dependence of 2P and 1S excitons in ZnS and of 2P excitons in CdS. From these measurements precise values for the band-gap shifts were obtained. Further, in ZnS pressure-induced changes of the exciton binding energy and of the spherical valence-band parameter (derived from the 2P exciton fine structure) were observed. \textcopyright{} 1996 The American Physical Society.

We have measured the effect of changing the copper isotope on the gap of CuCl and found that it decreases with increasing mass, contrary to observations in other tetrahedral semiconductors. Also, the direct gap of CuCl is found to increase anomalously (i.e., strongly nonlinearly) with increasing temperature. We show that both effects are related to electron-phonon renormalization of the electronic structure. A semiempirical theory is presented which explains these anomalies as due to an opposite sign of the effect on the gap of the copper and the halogen vibrations.

Two-photon spectroscopy has been used to determine the pressure dependence of band-structure parameters such as band gap, exciton binding energy, biexciton binding energy, exchange energy, and Luttinger parameters. Compared to linear spectroscopy it yields not only a higher precision, but is often able to determine a larger number of parameters. Results are presented for ZnTe and CuCl nanocrystals in a LiCl matrix.

Two-photon measurements were performed in AgGaS2 under hydrostatic pressures up to 8 GPa. In both the low-pressure phase (chalcopyrite structure) and the high-pressure phase (above 3.8 GPa, unknown structure), the pressure dependences of the band gap and of the exciton binding energy were determined. Additionally, in the chalcopyrite phase the exchange energy was measured as a function of pressure.