A. P. Skvortsov

Multiplicity of europium centers in doped stoichiometric crystals of lithium niobate

The optical spectra of europium-doped stoichiometric lithium niobate (LiNbO3:Eu3+) crystals have been studied using combined excitation-luminescence spectroscopy in the range of 5D0 → 7F1, 7F0 optical transitions. Analysis of the results shows that Eu3+ ions can occupy 14 energetically nonequivalent positions in the LiNbO3 crystal lattice. This multiplicity of impurity centers is related to possible variants of the incorporation of Eu3+ ions into the LiNbO3 crystal lattice and the compensation of excess charge. Energy positions of the 5D0 level and the lowest sublevel of the 7F1 Stark multiplet are determined for Eu3+ centers of all 14 types.

Light emission from erbium-doped nanostructures embedded in silicon microcavities

Abstract We present the findings of high-efficient Er 3+ -related 4 I 13/2 ↔ 4 I 15/2 absorption and emission from self-assembled quantum wells (SQW) embedded in silicon microcavities. The microcavities are prepared by the short-time diffusion of boron into the Si (1 0 0) wafer doped with erbium. The intraband electron transitions accompanied by tunneling through strongly coupled SQW series are observed to excite the 4 I 13/2 ↔ 4 I 15/2 Er 3+ -intracenter emission, 1.54 μm , that is enhanced by strong sp–f mixing in the range of the Rabi splitting revealed by the transmission spectra.

Optical absorption spectra and energy levels of Er3+ ions in KTaO3 crystals

The optical absorption spectra of erbium-doped potassium tantalate (KTaO3:Er) crystals have been studied. Absorption lines corresponding to the intraconfiguration f-f electron transitions from the 4I15/2 ground state to the levels of 4F9/2, 4S3/2,2H11/2, 4F7/2, 4F5/2(4F3/2), 2H9/2, and 4G11/2 excited states of Er3+ ions have been observed in a wavelength range of 350–660 nm. The transitions to 4F9/2, 2H11/2, 4F7/2, and 2H9/2 levels have been studied in detail at T = 2 K. Based on the obtained results, it is suggested that Er3+ impurity centers of two types exist in KTaO3:Er3+ crystals. The number of lines observed for the major type centers corresponds to that theoretically possible for Er3+ ions in a noncubic crystal field with a local compensation of the impurity charge. The energy positions of the levels of excited states for the observed transitions are determined.

Absorption spectra of bulk aluminum nitride crystals doped with Er3+ ions

This Letter presents results of analysis of the absorption spectra of AlN:Er3+ bulk crystals. In the spectral of 370–700 nm, absorption lines responsible for intraconfiguration electron transition from the ground state 4I15/2 to the excited states of Er3+ ions are found. Transitions to the levels of the 4F9/2, 2H11/2, and 4G11/2 states at 2 K are studied in detail. The number of observed lines for these transitions fully agrees with that theoretically possible for f–f electron transitions in Er3+ ions found in a noncubic crystal field. The small width of the observed lines and their number indicate that erbium ions displace mostly one regular crystal position. Most probably, Er3+ occupies the position of Al. Energy positions of excited states for the considered transitions are determined.

Absorption spectra of Er3+ ions in Li6Y(BO3)3 crystals

The optical absorption spectra of Li6Y(BO3)3:Er3+ crystals have been studied. The absorption lines corresponding to intraconfiguration electronic transitions from the 4I15/2 ground state to the levels of excited states of Er3+ ions have been found in the spectral range of 370–700 nm. The transitions to the 4F9/2, 4S3/2, 2H11/2, 4F7/2, 4F5/2, 4F3/2, 2H9/2, and 4G11/2 levels have been investigated in detail at 2 K. The number of lines observed for these transitions corresponds to the theoretical maximum for the f-f electronic transitions in Er3+ ions located in the noncubic crystal field. The narrowness of the lines observed and their number indicate that erbium occupies one regular position (specifically, the yttrium position). The energy levels of the excited states have been determined for the transitions under study.

Infrared and ESR spectroscopy of KTaO3 : Er

Infrared reflection and ESR spectra of KTaO3 : Er3+ single crystals have been investigated. The frequency of the lowest optical phonon mode TO1 has been found to increase as compared to undoped KTaO3 crystals, which indicates the suppression of the ferroelectric instability of the system. The ESR spectra have revealed the presence of two Er3+ centers of different (cubic and non-cubic) symmetries in KTaO3 : Er3+.

Li-impurity effect in optical spectra of KTaO3:Er3+ crystals

The f–f absorption and emission spectra of Er3+ impurities were observed and identified in KTaO3 and K1 – xLixTaO3 single crystals. It was shown that Li off-centers related random fields markedly influence intensity, width and position of zero-phonon lines. The detail analysis of the absorption spectra obtained allowed one to determine energies of the Stark sublevels of excited states for Er3+ dominant centers of noncubic symmetry.

Absorption spectra of GaN:Er3+ crystals

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.

The absorption spectra of gallium nitride crystals doped with erbium ions

We have measured the absorption spectra of Er3+ ions introduced by diffusion into bulk GaN crystals grown by vapor phase epitaxy in a chloride system. The wavelength interval of 518–527 nm corresponding to the region of the 4I15/2→2H11/2 transition was studied in detail at 293, 77, and 2 K. At 2 K, the spectrum of this transition displays six lines, which correspond to the theoretically possible number of sublevels of the 2H11/2 state of Er3+ ion occurring in a noncubic crystal field. The positions of levels in the 2H11/2 multiplet correspond to 2.360, 2.361, 2.365, 2.369, 2.379, and 2.386 eV. Both the number and narrow width of lines observed at 2 K indicate that Er3+ ions predominantly occupy the same regular position in GaN crystals. Most probably, erbium ions occupy gallium sites in the crystal lattice.

Light emission from erbium- doped nanostructures embedded in silicon microcavities

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