Igor N. Ogorodnikov

Low-temperature time-resolved vacuum ultraviolet luminescent spectroscopy of KH2PO4 crystals with defects

Low-temperature photoluminescence (PL) of unactivated KDP crystals under selective synchrotron excitation is for the first time measured with subnanosecond time resolution. Time-resolved PL (2–6 eV) and PL excitation (4–35 eV) spectra, as well as PL kinetics, are measured at 7 K. From the acquired experimental data, luminescent bands related to intrinsic defects of the KDP lattice are identified; in particular, the long-wave band at 2.6 eV is assigned to L defects, and the band at 3.5–3.6 eV is attributed to D defects. An efficient energy transfer over the hydrogen sublattice is shown to take place in KDP at low temperatures. It results in the efficient excitation of L and D center photoluminescence in the fundamental absorption region, at electron transitions to the bottom levels of the conduction band, corresponding to the states of the hydrogen atom. The band gap Eg is evaluated to be 8.0–8.8 eV.

Sub-nanosecond time-resolved spectroscopy of LiB3O5 under synchrotron radiation

Abstract This paper presents the results of study of luminescence of the LiB3O5 crystals excited with synchrotron radiation. It was revealed that LiB3O5 exhibits a polarized fast luminescence with the complex broad band peaked in the spectral region 3.5–4.2 eV. Time response of the luminescence demonstrates both the fast exponential component with the time constant of 1.2 ± 0.2 ns (300 K) or 1.3 ± 0.3 ns (80 K) and several slow components in the microsecond time range. The paper discusses the origin and excitation channels for the broad-band luminescence in LiB3O5 crystals.

Luminescence of impurity-bound excitons in Li6GdB3O9:Ce3+ single crystals

The anomalous (τ < 10 ns) luminescence of wide bandgap crystals of lithium-gadolinium orthoborate Li(6)GdB(3)O(9) doped with trivalent cerium ions, has been revealed for the first time and investigated through the low-temperature time-resolved vacuum ultraviolet synchrotron spectroscopy. It was shown that the optical transitions at 6.2 eV are due to electron transfer from the ground 4f(1) states of Ce(3+) ion onto the autoionized states near the conduction band bottom of a crystal. These transitions lead to the formation of impurity-bound excitons in the form of correlated electron-hole pair, in which the hole component is localized at 4f-level of the cerium ion and an electron component is located at the conduction band bottom in the attractive potential of this hole. It is established that the direct radiative recombination of the cerium impurity-bound exciton leads to a fast broadband emission at 4.25 eV. The energy threshold for creation of the impurity-bound excitons was determined on the basis of the obtained spectroscopic data. We calculated the H(k) functions of distribution of the elementary relaxations over the reaction rate constants and explained on this basis the decay kinetics and quenching processes, not only for the anomalous emission at 4.25 eV, but for the ordinary 5d-4f luminescence at 3.0 eV in Ce(3+) ions. The paper discusses the decay channels for the impurity-bound excitons and their influence on the decay kinetics and spectra of luminescence in Li(6)GdB(3)O(9) crystals.