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A detailed analysis of photoluminescence of Eu-doped Na0.5Bi0.5TiO3 (NBT) is performed using it as a tool for describing the local structure of NBT. The obtained results reveal the low symmetry of the Eu3+ local environment in NBT, as indicated by the observed maximal number of sublevels of the 5D0→7F1 and the 5D0→7F2 luminescence transitions, clearly observed at low temperatures. Approximation of the luminescence spectra by Gaussian peaks provides valuable information about the shift of the involved levels upon change of the excitation wavelength. Variation in the strength of the crystal field in Eu-doped NBT is evaluated. Temperature dependence of the luminescence above room temperature is analyzed for the poled and the unpoled states of the material. The results obtained for Eu-doped NBT are compared with the results for Er-doped NBT reported previously. [ABSTRACT FROM AUTHOR]

Photoluminescence in Er-doped NBT is studied at different temperatures. Remarkable reduction of the luminescence intensity in the green spectral range is found in the poled state comparing with the depoled state. Luminescence spectra at low temperatures reveal continuous wavelength shift of some maxima belonging to the 4 S 3/2  →  4 I 15/2 transition depending on the excitation wavelength, which is explained by large variety of different environments around Er 3+ related to the random distribution of Na + and Bi 3+ in A-sublattice of the ABO 3 perovskite structure. Poling extends the wavelength range where shift of luminescence maxima is observed in the direction of longer excitation wavelengths. This feature can be explained by more ordered structure characteristic to the poled state comparing with the depoled one. Luminescence spectra of Er-doped BaTiO 3 are also measured at low temperatures, and confirm the role of Na + and Bi 3+ ion disorder in the observed spectral features of Er-doped NBT. [ABSTRACT FROM AUTHOR]

In this paper a novel method for synthesis of LaInO3: Er3+ is reported and upconversion luminescence properties of the synthesized material at different temperatures (9-300 K) are studied. The samples were prepared by co-precipitation and subsequent heat treatment of lanthanum, indium and erbium hydroxides. It is shown that the excitation at 980 nm leads to a strong green upconversion luminescence in the material. At the concentrations above 0.1 mol. % of Er3+ the energy transfer upconversion mechanism of the luminescence becomes evident. Further increase of Er3+ content in the material leads to higher red-to-green upconversion luminescence intensity ratio. The mechanisms responsible for the observed variation are discussed. [ABSTRACT FROM AUTHOR]

Low-temperature ultraviolet-excited photoluminescence (PL) and recombination luminescence (RL) properties of La-doped Ca 2 SnO 4 have been investigated by luminescence, electron paramagnetic resonance (EPR) and optically-detected magnetic resonance (ODMR) techniques. Two PL and RL bands at 340 nm and 450 nm have been observed. PL excitation spectra measurements with a synchrotron source showed a significant difference between the 450 nm and the 340 nm PL bands. The 450 nm band has a long-lasting hyperbolic decay, while the 350 nm band shows a fast decay. Assuming an excitonic nature of the 340 nm band, the band gap of the Ca 2 SnO 4 :La has been estimated to be approximately 5.5 eV. ODMR measurements suggest that the low-temperature RL band at 450 nm is caused by tunnelling recombination of electron trap and hole trap centres, and the recombination energy is transferred to Sn2+ luminescence centres. • Ca 2 SnO 4 :La exhibits a long-lasting afterglow at low temperatures. • ODMR techniques show that afterglow originates from recombination of F-type and V-type centres. • Band gap energy of 5.5 eV is estimated from luminescence excitation measurements. [ABSTRACT FROM AUTHOR]

Different compositions of europium doped aluminosilicate oxyfluoride glass ceramics prepared in air atmosphere have been studied by electron paramagnetic resonance (EPR) and optical spectroscopy methods. X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements show presence of homogenously distributed SrF 2 nanocrystals after the heat treatment of the precursor glass. Efficient Eu 3+ incorporation in the high symmetry environment of glass ceramics is observed from the photoluminescence spectra. EPR spectra indicate Eu 3+ → Eu 2+ reduction upon precipitation of crystalline phases in the glass matrix. For composition abundant with Eu 2+ in the glassy state such behaviour is not detected. Local structure around europium ions is discussed based on differences in chemical compositions. [ABSTRACT FROM AUTHOR]

In this paper, we have performed comparative analysis of EPR, optical absorption (OA) and luminescence spectra for a series of Gd 3 Ga 5 O 12 (GGG) single crystals irradiated with fast neutrons with fluencies varied from 1016 to 1020n/cm2. In a crystal irradiated with the maximum neutron fluence, the EPR spectra demonstrated the formation of several paramagnetic defects. In particular, EPR spectrum shows a strong resonance at (effective) g ≈ 1.4 with practically isotropic behavior in the crystal rotation around the [1 1 1] direction (magnetic field being perpendicular to [1 1 1]) and several weaker lines in the g ≈ 1.1–2.6 region, which show more pronounced angular dependences. While the photoluminescence of non-irradiated GGG is characterized by uncontrolled impurities, in the case of neutron-irradiated GGG, a broad asymmetric luminescence band was observed with a peak at 725–733 nm, which increased with fluence. Consequently, this band can be associated with the formation of radiation defects. [ABSTRACT FROM AUTHOR]

In this paper a novel method for synthesis of LaInO3: Er3+ is reported and upconversion luminescence properties of the synthesized material at different temperatures (9-300 K) are studied. The samples were prepared by co-precipitation and subsequent heat treatment of lanthanum, indium and erbium hydroxides. It is shown that the excitation at 980 nm leads to a strong green upconversion luminescence in the material. At the concentrations above 0.1 mol. % of Er3+ the energy transfer upconversion mechanism of the luminescence becomes evident. Further increase of Er3+ content in the material leads to higher red-to-green upconversion luminescence intensity ratio. The mechanisms responsible for the observed variation are discussed. [ABSTRACT FROM AUTHOR]