We have studied the f-f absorption spectra of Er3+ in GaN crystal grown by gas phase epitaxy in chlorine system. A detailed study of 4I15/2 yields 2H11/2 transitions in the region 19000-19260 cm-1, has been carried out at 293, 77 and 2K. At T equals 2K the 4I15/2 yields 2H11/2 spectrum contains 6 lines in accordance with theoretical predictions for Er3+ in noncubic crystal field. The levels of 2H11/2 multiplet are situated at: 19041, 19049, 19074, 19108, 19191, 19246 cm-1. The number of lines observed at T equals 2K and its small width indicate that in our samples Er3+ ions occupy predominantly a unique position in GaN lattice. Most probably, Er3+ substitutes Ga atoms or enters in interstitial position.
We present the findings of high efficient light absorption in self-assembled quantum wells (SQW) embedded in silicon microcavities that exhibit a distributed feedback identified by the FIR transmission spectra. The photo and electroluminescence from SQW is found to be enhanced in the range of the Rabi splitting. The intraband hole transitions are shown to give rise to a fast energy transfer into the d- shell transitions of the center incorporated into the microcavity which is caused by strong sp-d mixing in built- in electric field and revealed by the intracenter emission. Besides, high efficient Er3+-related 4I13/2 $ARLR 4I15/2 absorption and emission a re observed from self-assembled quantum wells (SQW) embedded in silicon microcavities. The microcavities of this art are prepared by the short-time diffusion of boron into the Si(100) wafer doped with erbium. The intraband electron transitions accompanied by tunneling through strongly coupled SQW series are found to excite the 4I13/2 yields 4I15/2Er3+-intracenter emission that is enhanced in the range of the Rabi splitting revealed by the transmission spectra.
The effect of external electric field on the absorption spectra of LiNbO3 crystals doped with Nd3+ and Cr3+ ions has been investigated at 77 K by means of sensitive modulation method. A linear Stark effect is observed on many lines of Nd3+ and on B-lines of Cr3+-centers in a field directed along the trigonal axis of the crystal. No field effect is observed in a field directed perpendicular to the trigonal axis. Such properties of the Stark effect show that the permanent dipole moments of Nd3+ and Cr3+ centers are oriented along the trigonal axis of the crystal. This confirms that the centers possess C3 point symmetry. The quantitative characteristics of the field effect are determined.
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