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The luminescent Z-scan technique with time resolution is applied to the study of the luminescence properties of CH3NH3PbBr3 single crystals representative of the family of hybrid organic–inorganic lead perovskites successfully applied recently in photovoltaics and currently investigated as potential nanosecond scintillators. The third harmonic of Ti-sapphire laser (λ = 266 nm) with a pulse duration of 26 fs and 1 kHz frequency was applied for the luminescence excitation creating the charge carriers with the estimated density from 1017 to 1021 cm−3 in the temperature range from 13 to 300 K. Temperature and excitation density dependence of the luminescence yield and kinetics is interpreted with the consideration of the temperature-dependent binding of electrons and holes into excitons, a saturation of defects responsible for the non-radiative relaxation channel competing with exciton creation; absorption saturation resulting in the increased penetration depth of the excitation radiation and hence the increased contribution of the re-absorption. [ABSTRACT FROM AUTHOR]

Two series of (Gd, Y, Yb)3Al2Ga3O12 quintuple compounds with a garnet structure and solely doped with Ce and Tb were prepared in the form of ceramics by sintering in oxygen at 1600 °C for two hours and studied for the interaction of activator ions with ytterbium ions entering the matrix. It was shown that the photoluminescence and scintillation of Ce3+ ions are completely suppressed, predominantly by tunneling ionization through the charge transfer state (CTS) of the Ce4+-Yb2+ ions. The photoluminescence of Tb3+ ions is quenched in the presence of ytterbium, but not completely due to the poor resonance conditions of Tb3+ intraconfiguration transitions and the CTS of the single Yb3+ and the CTS of Ce4+-Yb2+ ions. The scintillation in the visible range of both Ce3+- and Tb3+-doped samples is intensely quenched as well, which indicates strong competition from Yb3+ ions to activators in interaction with the Gd substrate. [ABSTRACT FROM AUTHOR]

A mechanism of firefly high‐scintillation light yield (LY) of Tb‐doped quaternary (Gd, Y)3Al2Ga3O12 garnet ceramics is reported. Through measurements with the synchrotron source, the high efficiency of the luminescence excitation, providing a quantum yield Q > 1 below the photon multiplication energy range, is defined. The excitation efficiency reaches two at the excitation energy slightly above 2Eg. The cascade of photons is explained by combining three factors: first, the high quantum yield Q ≈ 1 of the luminescence at excitation in lower mixed states 4f75d1 with high spin (HS) and low spin (LS); second, the cross‐relaxation 4f7(6P)5d1(HS) → 4f7(8S)5d1(HS) provides the excitation of 4f8(7F0) →4f8(5D1,4) transition of the 4f8 configuration of the same or neighboring Tb ion, which is followed by the luminescence from 5D1,4; and finally, the relaxation of 4f7(8S)5d1‐5(HS) configuration into the excited 4f8 configuration occurs with future emission from 4f8(5D1,4) states. This cascade forms the final stage of the scintillation in the compound being studied and provides a LY twice as high compared with the material when doped with Ce. [ABSTRACT FROM AUTHOR]

Technological factors and processes contributing to the scintillation mechanism have been considered in quaternary garnet ceramics doped with Ce(Gd,Lu)3Al2Ga3O12. The super-stoichiometric additive of gadolinium in the material composition or its co-doping with a low concentration of Mg were found to be effective tools to suppress phosphorescence in the quaternary garnet, confirming that it is not an intrinsic property of the material. The Monte-Carlo simulation of electronic excitation transfer demonstrates that the hopping migration along the gadolinium sublattice plays an essential role in forming the scintillation kinetic parameters. Breaking the integrity of the gadolinium sublattice by substitution with heavier lutetium ions increases the role of self-trapped states in the excitation of Ce3+ ions, which ensures both an increase in the fraction of short ~20 ns and very long ~600 ns components in the scintillation kinetics. [ABSTRACT FROM AUTHOR]

Thin-film diamond–rare earth fluoride nanocomposites have been produced by chemical vapor deposition to be used as a source of intensive photo- and X-ray luminescence. The composites with embedded Eu-containing nanoparticles show high-intensity orange narrow-band photoluminescence near the wavelength of 612 nm. Using β-NaGdF4:Eu instead of Eu-(III) tri-(2,6-pyridine dicarboxylic acid) and europium fluoride in the diamond matrix resulted in enhanced signal/noise ratio in the luminescence. The mapping of the spatial distribution of photoluminescence intensity on macro- and micro scale revealed highly uniform emission originated from the composite. The developed composite material with mechanically strong, highly thermally conducting and transparent diamond matrix opens a way to use the diamond–fluoride composites as photo- and X-ray luminescent screens (scintillators) capable to withstand high photon fluxes. [ABSTRACT FROM AUTHOR]

A comparative study of structural properties, photoluminescence and electrical conductivity of SiO xN y/SiO2, SiO xN y/Si3N4 and SiN x/Si3N4 superlattices is presented. The samples were prepared by plasma enhanced chemical vapor deposition and annealed at 1150 °C in order to produce arrays of silicon nanocrystals, with their formation being confirmed by X-ray diffraction analysis and photoluminescence spectroscopy. Reference samples without silicon nanocrystals were also fabricated by annealing of as-prepared films at a lower temperature (700 °C). All high temperature -annealed samples are characterized by similar photoluminescence spectra with the maxima in the range from 1.3 to 1.6 eV, which were attributed to Si nanocrystals. The peak position, as well as photoluminescence lifetime in the microsecond range, point to the quantum confined origin of the emission. Current-voltage measurements revealed an increase in conductivity by several orders of magnitude for the samples with Si nanocrystals in SiN x/Si3N4 superlattices as compared to both SiO xN y/Si3N4 and SiO xN y/SiO2 films, as well as to low temperature annealed counterparts. The dependence of the conduction mechanism in superlattices on their structural properties is discussed. [ABSTRACT FROM AUTHOR]

Luminescence emission and excitation spectra as well as decay kinetics of Y2O3-Yb nanoparticles elaborated by the polyol mediated synthesis method have been measured at liquid helium temperature under VUV excitation. In nanoparticles the ratio of intensities of Charge Transfer Luminescence (CTL) and exciton excitation peaks differs from that for Y2O3-Yb single crystal, and changes with the particle size variation from 13 to 52 nm. This effect can be connected with the variation of excitation light scattering with particle dimensions. Two types of luminescence decay acceleration are observed. Acceleration of exponential decay time with decrease of nanoparticle size and the appearance of very fast decay component in small nanoparticles that we connected to energy transfer to the surface defects. [ABSTRACT FROM AUTHOR]