ELECTRICAL INSTABILITY IN RUBY UNDER OPTICAL PUMPING

The new phenomenon consists in a spontaneous appearance in strongly excited concentrated ruby of domains with strong (~ MV/cm) electric fields of opposite sign which persist for a long time after the termination of pumping. The photoinduced formation of domains was found to depend critically on external conditions (temperature, external electric field, pumping rate and wavelength of optical excitation), as well as on the chromium concentration. Photocurrent measurements support the phenomenological interpretation of the phenomenon as a result of an electrical instability caused by the negative, absolute and differential, conductivity of concentrated ruby under optical excitation

PHONONS IN EXCITED RUBY

New results concerning the properties of acoustic phonons 0.87 THz in ruby are considered including (1) attenuation and anharmonic scattering of ballistic phonons and (2) kinetics of resonance phonon trapping

MULTIPLE RESONANT RAMAN SPIN-FLIP PHONON SCATTERING AND 29 CM-1 PHONON TRANSPORT IN EXCITED RUBY IN A MAGNETIC FIELD

The paper reports on the observation of an anomalous nonmonotonic dependence of trapping of the 29 cm-1 phonons on magnetic field. The effect is due to inelastic phonon scattering processes involving the creation (absorption) of a Zeeman quantum of the E-level (resonance spin-flip phonon Raman scattering) /1/

Inhomogeneous Broadening: Symmetry of Centers and Disorder in Solid Solutions and Nanocrystals

Zero-phonon electronic transitions of Cr3+ impurity ions in solid solutions and nanocrystals are studied. In the series of Lu3xY3-3xAl5O12 (0<x<1) garnet solid solution crystals the modification of zero-phonon R-line (2E–4A2) fluorescence spectra of Cr3+ ions with changing x occurs in a discrete fashion and is not accompanied by strong inhomogeneous broadening. The effect is ascribed to high C3i symmetry of Cr3+(Al3+) sites. The fluorescence line narrowing experiments were performed for the inhomogeneously-broadened R-line of cubic Cr3+ centers in MgO nanocrystals. The inhomogeneous broadening in nanocrystals is attributed to spatial confinement

Inhomogeneous Broadening: Symmetry of Centers and Disorder in Solid Solutions and Nanocrystals

Zero-phonon electronic transitions of Cr3+ impurity ions in solid solutions and nanocrystals are studied. In the series of Lu3xY3-3xAl5O12 (0<x<1) garnet solid solution crystals the modification of zero-phonon R-line (2E–4A2) fluorescence spectra of Cr3+ ions with changing x occurs in a discrete fashion and is not accompanied by strong inhomogeneous broadening. The effect is ascribed to high C3i symmetry of Cr3+(Al3+) sites. The fluorescence line narrowing experiments were performed for the inhomogeneously-broadened R-line of cubic Cr3+ centers in MgO nanocrystals. The inhomogeneous broadening in nanocrystals is attributed to spatial confinement