Phase transition, radio- and photoluminescence of K3Lu(PO4)2 doped with Pr3+ ions

Luminescent characteristics of K3Lu(PO4)2:Pr3+ (1 and 5 mol.%) microcrystalline powders, a promising optical material for scintillation applications, were investigated using various experimental techniques. The material shows emission features connected with both high intensity interconfigurational 4f15d→4f2 transitions (broad UV emission bands) and intraconfigurational 4f2→4f2 transitions (weak emission lines in the visible range). The output of X-ray excited 4f15d→4f2 emission of Pr3+ increases with a temperature rise from 90 K to room tem- perature and higher depending on the Pr3+ ions concentration. The high 5% concentration of Pr3+ ions is found to be favourable for the stabilization of a monoclinic phase (P21/m space group) over a trigonal one (P3 space group) while emission properties of the material reveal that a phase transition occurs at higher temperatures. Decay kinetics of Pr3+ 4f15d→4f2 emission are recorded upon excitation with high repetition rate X-ray syn- chrotron excitation and pulse cathode ray excitation. Issues related to a non-exponential decay of luminescence and presence of slow decay components are discussed in terms of energy transfer dynamics. The presence of defects was revealed with thermoluminescence measurements and these are suggested to be the mainly responsible for delayed recombination of charge carriers on the Pr3+ 4f15d states. Some peculiarities of host-to- impurity energy transfer are discusse

Identification of the nature of traps involved in the field cycling of Hf₀.₅Zr₀.₅O₂-based ferroelectric thin films

The discovery of ferroelectricity in hafnium oxide has revived the interest in ferroelectric memories as a viable option for low power non-volatile memories. However, due to the high coercive field of ferroelectric hafnium oxide, instabilities in the field cycling process are commonly observed and explained by the defect movement, defect generation and field induced phase transitions. In this work, the optical and transport experiments are combined with ab-initio simulations and transport modeling to validate that the defects which act as charge traps in ferroelectric active layers are oxygen vacancies. A new oxygen vacancy generation leads to a fast growth of leakage currents and a consequent degradation of the ferroelectric response in Hf₀.₅Zr₀.₅O₂ films. Two possible pathways of the Hf₀.₅Zr₀.₅O₂ ferroelectric property degradation are discussed

Optical and Electronic Properties of Undoped La2Be2O5La_2Be_2O_5 Single Crystals in the Far Ultraviolet Energy Range

The optical and electronic properties of undoped $La_{2}Be_{2}O_{5}$ single crystals were determined using low-temperature ($\mathit{T}$=10  K) far ultraviolet (4.9–33 eV) synchrotron radiation spectroscopy, optical absorption spectroscopy (=80 and 320 K), and calculations for the dispersions of the optical functions. On the basis of the obtained data we determined the Urbach’s formula parameters and the cut-off energy $\mathit{E_{e}}$=5.49  eV at 80 K for the low-energy tail of the host absorption, the bandgap $\mathit{E_{g}}$=6.78  eV at 10 K, the energy threshold for the creation of unrelaxed excitons $\mathit{E_{ex}}$=6.28  eV, and other electronic properties

Photoluminescence of nanostructured Zn2SiO4:Mn2+\mathrm{Zn_2SiO_4:Mn^{2+}} ceramics under UV and VUV excitation

The photoluminescence of Zn$_2$SiO$_4$:Mn$^{2+}$ ceramics with a particle size of 120 ± 10 nm, which is excited in the range of 3.5–5.8 eV and subjected to synchrotron radiation with photon energies of up to 20 eV, is investigated. Nanoscale Zn$_2$SiO$_4$:Mn$^{2+}$ ceramics possesses intense luminescence with a maximum of 2.34 eV, the position and half-width of the band are independent of the excitation energy. It is found that the photoluminescence at 2.34 eV decays nonexponentially upon ultraviolet excitation. In the case of nanoscale ceramics is irradiated by vacuum ultraviolet, an additional photoluminescence-excitation channel is likely to occur due to interaction of band states and intrinsic vacancy-like defects of the Zn$_2$SiO$_4$ matrix

Optical and luminescence characterization of LiBaAlF6 single crystals

Far ultraviolet optical, luminescence excitation and pulse cathodoluminescence spectroscopy methods were used to determine the electronic structure properties of undoped single crystals of LiBaAlF6 (LBAF). The spectrum of the refraction index in the ultraviolet–visible range was recorded. The photoluminescence excitation spectroscopy was carried out for both the excitonic (4.3 eV) and fast vacuum ultraviolet (6.6 eV) emission bands of LBAF single crystals at 10 K. Modeling of the photoluminescence excitation spectra for excitonic emission was performed to characterize the low-energy tail of the host absorption of LBAF single crystals. The pulse cathodoluminescence spectroscopy method was used to characterize the fast vacuum ultraviolet (6.6 eV) emission band and proof its origination from the radiative core-valence transitions F− 2p →→ Ba2+ 5p

Unraveling Pr3+ 5d-4f emission in LiLa9(SiO4)6O2 crystals doped with Pr3+ ions

LiLa9(SiO4)(6)O-2 (LLSO) crystals doped with Pr3+ ions were grown using the slow cooling flux method. The crystals were characterized by means of luminescence and optical spectroscopy and luminescence decay measurements upon excitation in UV, VUV and X-ray range including using synchrotron radiation sources. The spectroscopic data revealed the presence Pr3+ 5d <-> 4f emission and excitation bands related to Pr3+ ions replacing La3+ i n two nonequivalent positions, and features related Pr3+ 4f -> 4f emission. The photon cascade emission is not observed in LLSO:Pr3+, since Pr3+ S-1(0) state is above the bottom of 4f(n-1)5d mixed-states band. Apart from the emission features related to Pr3+, a defect-related emission was observed upon UV, VUV, and ionizing radiation excitation. Presence of the defects was shown with thermoluminescence measurements and suggested to be the main reason for suppression the 5d -> 4f emission. Peculiarities of host-to-impurity energy transfer are analyzed and discussed

Luminescence of LaBr3LaBr_3 :Ce,Hf scintillation crystals under UV-VUV and X-ray excitation

The present study was carried out by means of the low temperature time-resolved luminescence UV–VUV spectroscopy as well as the optical and thermally activation spectroscopy. The Ce3+ centers in regular lattice sites and located in the vicinity of the point defects of crystal structure were observed. Spectral and kinetic characteristics of the luminescence of these centers were defined. A photoluminescence of new point defects of the crystal structure are also manifested. We evaluated the energy of the interband transitions as Eg ≈ 6.2 eV in LaBr3. At the excitation energies Eexc>13 eV (higher than 2Eg) the effect of the electronic excitations multiplication was detected

Optical properties of KPb2Cl5KPb_2Cl_5 and RbPb2Cl5RbPb_2Cl_5 single crystals in the far ultraviolet spectral region

Electronic structure properties of undoped single crystals of KPb2Cl5 (KPC) and RbPb2Cl5 (RPC) have been studied using low-temperature (T=8°K) far ultraviolet (3.7–24 eV) synchrotron radiation spectroscopy. Dispersions of optical functions have been calculated. The electronic transitions at 4.4–5.0 eV were ascribed to the excitation of cationic excitons. The energy region of 5–9 eV was associated with the transitions from the valence band to the conduction band: 6S10→6P11 at 6.28 eV, 6S10→6P32 at 5.94 eV. The complex band at 7.87 eV was attributed to the excitation of anionic excitons. The 19–24 eV peaks were associated with the 5d→6p transitions in Pb2+ ions