S. A. Zhurkov

Luminescence and electronic excitations in Li6Gd(BO3)3: Ce3+ crystals

This paper reports on a study of the luminescence emitted by Li6Gd(BO3)3: Ce3+ crystals under selective photoexcitation to lower excited states of the host ion Gd3+ and impurity ion Ce3+ within the 100–500-K temperature interval, where the mechanisms of migration and relaxation of electronic excitation energy have been shown to undergo noticeable changes. The monotonic 10–15-fold increase in intensity of the luminescence band at 3.97 eV has been explained within a model describing two competing processes, namely, migration of electronic excitation energy over chains of Gd3+ ions and vibrational energy relaxation between the 6Ij and 6Pj levels. It has been shown that radiative transitions in Ce3+ ions from the lower excited state 5d1 to 2F5/2 and 2F7/2 levels of the ground state produce two photoluminescence bands, at 2.08 and 2.38 eV (Ce1 center) and 2.88 and 3.13 eV (Ce2 center). Possible models of the Ce1 and Ce2 luminescence centers have been discussed.

Thermodynamic properties and structure of oxyfluorides Rb2KMoO3F3 and K2NaMoO3F3

According to the results of calorimetric and structural studies, the Fm{ie1202-1}m phase in K2NaMoO3F3 remains stable at least to 100 K. No ferroelectric transformation assumed earlier has been revealed in a series of Rb2KMoO3F3 samples prepared using various technologies. Only a phase transition of nonferroelectric origin has been observed near 195 K, and its thermodynamic characteristics have been determined. An analysis of the stability of the cubic structure of molybdenum fluorine-oxygen elpasolites-cryolites has been performed in the framework of the hypothesis on strengths of interatomic bonds. The barocaloric effect in Rb2KMoO3F3 has been estimated.

Luminescence and electronic excitations in KBe2BO3F2 crystals

This paper reports on a study of the dynamics of electronic excitations in KBe2BO3F2 (KBBF) crystals by low-temperature luminescent vacuum ultraviolet spectroscopy with nanosecond time resolution under photoexcitation by synchrotron radiation. The first data have been obtained on the kinetics of photoluminescence (PL) decay, time-resolved PL spectra, time-resolved PL excitation spectra, and reflection spectra at 7 K; the estimation has been performed for the band gap Eg = 10.6−11.0 eV; the predominantly excitonic mechanism for PL excitation at 3.88 eV has been identified; and defect luminescence bands at 3.03 and 4.30 eV have been revealed. The channels of generation and decay of electronic excitations in KBBF crystals have been discussed.

Electronic structure of KTiOAsO4, a novel material for non-linear optical applications

A high-quality KTiOAsO4 (KTA) single crystal has been successfully synthesized employing the high temperature solution growth technique with rotating and pooling. The XPS valence-band spectra have been measured for pristine and the 1.5 keV Ar+ ion-bombarded thin (001)KTA plate cut from the crystal part that was without any optical inhomogeneities or domain boundaries. The present XPS measurements have revealed the existence of two O 2s subbands on the XPS spectrum of the pristine (001)KTA surface. It has been established that 1.5 keV Ar+ ion bombardment of the (001)KTA surface causes the complete elimination of the O 2s sub-band related to oxygen atoms involved in the formation of Ti–O–As bonds in KTA. In addition, the XPS results reveal that such a treatment leads to a significant decrease of the relative intensity of the XPS As5+ 3d core-level spectrum and causes the formation of the additional As0 3d core-level spectrum in the topmost layer of the (001)KTA surface. The experimental data are compared to the results of the first-principles band-structure calculations of KTA.

Luminescence and electronic excitations in crystals K2Al2B2O7 with defects

This paper reports on the results of the comprehensive study of the dynamics of electronic excitations in K2Al2B2O7 (KABO) crystals, obtained by low-temperature luminescence vacuum ultraviolet spectroscopy with nanosecond time resolution upon photoexcitation by synchrotron radiation. For the first time, the data have been obtained on the photoluminescence (PL) decay kinetics, PL spectra with time resolution, PL excitation spectra with time resolution, and reflection spectra at 7 K; the intrinsic nature of PL at 3.28 eV has been established; luminescence bands of defects have been separated in the visible and ultraviolet spectral regions; an intense long-wavelength PL band has been detected at 1.72 eV; channels of the formation and decay of electronic excitations in K2Al2B2O7 crystals have been discussed.