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For the first time, the temperature evolution of the absorption spectra of Alq3 thin film, prepared by the method of vacuum thermal evaporation, was investigated in the range of 16–320 K. The optical energy gaps were obtained from direct allowed transitions at this temperature range by means of Tauc plots. [ABSTRACT FROM AUTHOR]

Halide perovskites recently emerged as promising materials for the detection of ionising radiation. Single crystals of halide perovskites exhibit very fast and bright scintillation when cooled and may outperform the best modern scintillators at temperatures below 100 K. In this work we report on low-temperature scintillation properties of CsPbCl3 single crystals, grown using the Bridgeman method. The temperature dependences of the luminescence and decay kinetics were studied using X-ray excitation. At low temperatures, the crystal exhibits an intense narrow-band emission at about 420 nm with very fast decay kinetics. This emission, of which a characteristic feature is the strong thermal quenching, is attributed to the radiative decays of bound and trapped excitons. The fast, middle, and slow decay time constants obtained from a fit of a sum of exponential functions to the decay curve at 10 K are 0.1, 1 and 11 ns, respectively. The scintillation light yield of CsPbCl3 at 7 K measured at excitation with α-particles from an 241Am source is estimated to be 140 ± 15% of a reference LYSO-Ce crystal and 19000 ± 2000 ph per MeV under 14 keV X-ray excitation at 10 K. It is concluded that owing to a reduced amplitude of the slow decay component, CsPbCl3 exhibits an ultra-fast scintillation response that is superior to that of other halide perovskites. The combination of sub-nanosecond response time and the encouraging light yield has the potential of establishing this material as first choice for scintillation applications that rely on prompt detector response at cryogenic temperatures. [ABSTRACT FROM AUTHOR]

We have obtained X-ray emission spectra of Ga and Ge in Ca3Ga2Ge4O14, X-ray emission OKα-spectra in Ca3Ga2Ge4O14, Ca3Ga2Ge4O14 + Ce3%, and Ca3Ga2Ge4O14 + Eu4% and Xray photoelectron spectra in Ca3Ga2Ge4O14 . Our X-ray spectral studies of the Ca3Ga2Ge4O14 gallogermanate have shown that the top of the valence band near the Fermi level is formed mainly by p states of gallium and germanium as well as p states of oxygen, whose intensity is sufficiently low. The middle of the valence band is formed by gallium 3d states with oxygen 2s states lying below them. These states are hybridized with 4p states of gallium and germanium because of which there are Kβ′′-satellites in the Kβ2-subbands of gallium and germanium. The bottom of the valence band is formed by 3d states of germanium, whose contribution to chemical bonding is insignificant. The X-ray emission bands of Ga and Ge in Ca3Ga2Ge4O14 and the photoelectron spectrum of the valence electrons of Ca3Ga2Ge4O14 are in good agreement. The OKα-band changes its fine structure only slightly upon doping Ca3Ga2Ge4O14 with Ce or Eu. The investigations of intrinsic luminescence under X-rays excitation of Ca3Ga2Ge4O14 gallogermanate are presented. [ABSTRACT FROM AUTHOR]

This work investigates temperature changes of the optical absorption edge of (NH4)2CuCl4·2H2O crystals in the region of the ferroelastoelectric (FEE) phase transition. The low-energy tail of the absorption edge in these materials shows an exponential shape. The temperature range above 200.5 K and below 100 K follows the empirical Urbach's rule. The obtained experimental data confirmed the existence of the FEE phase transition at 200.5 K. Nonfulfillment of Urbach's rule just below the phase transition temperature is explained by the scattering of light on the FEE domains. [ABSTRACT FROM AUTHOR]

Gallium oxide has recently been identified as a promising scintillator. To assess its potential as a detector material for ionizing radiation at low temperatures, we measured the luminescence and scintillation properties of an undoped Ga2O3 crystal over the 7–295 K temperature range. The emission of the crystal is due to the radiative decay of self-trapped excitons and donor-acceptor pairs and peaks at a wavelength of 380 nm. The scintillation light output of the undoped Ga2O3 increases with a decrease in temperature, reaching a maximum value of 19 300 ± 2200 ph/MeV at 50 K. The measured luminescence kinetics has a recombination character with specific decay time (τ0.1) increasing from 1 to 1.8 μs at cooling. Since radiative decay in the crystal competes with nonradiative processes, material optimization could lead to the scintillator achieving a yield of 40800 ph/MeV, a figure considered to be an upper limit. [ABSTRACT FROM AUTHOR]

On the basis of spectroscopic studies of (NH2(C2H5)2)2CoCl4 crystals, the absorption bands corresponding to the internal electronic transitions in the Co2+ ion were identified. The values of the crystal field and Racah parameters were calculated. The temperature evolution of the absorption spectra of (NH2(C2H5)2)2CoCl4 crystals reveals the anomalies of their parameters at the points of phase transitions. The corresponding changes of the absorption spectra were discussed in terms of distortion of the metal-halogen complex. The temperature dependences of the absorption spectra of (NH2(C2H5)2)2CoCl4 crystals confirm the presence of the thermochromic phase transitions at 255 and 330 K. [ABSTRACT FROM AUTHOR]

The results of the investigations of X-ray excitation spectra, thermostimulated luminescence and influence of light illumination on the thermoluminescence glow curves of Eu3+-doped Ca3-xCdxGa2Ge3O12 garnet polycrystalline samples are presented. It is shown that Ca3-xCdxGa2Ge3O12 polycrystalline samples are characterized by intrinsic luminescence, which consists of several components. The nature of intrinsic luminescence is discussed. It is suggested that the nature of thermoluminescence glow peak near 150 K is connected with the [(VGe+VO)--F+] associations formed under X-ray irradiation at 85 K. The influence of light illumination on the TSL intensity of the preliminary X-ray irradiated samples is shown. [ABSTRACT FROM AUTHOR]

We have obtained X-ray emission spectra of Ga and Ge in Ca3Ga2Ge4O14, X-ray emission OKα-spectra in Ca3Ga2Ge4O14, Ca3Ga2Ge4O14 + Ce3%, and Ca3Ga2Ge4O14 + Eu4% and Xray photoelectron spectra in Ca3Ga2Ge4O14 . Our X-ray spectral studies of the Ca3Ga2Ge4O14 gallogermanate have shown that the top of the valence band near the Fermi level is formed mainly by p states of gallium and germanium as well as p states of oxygen, whose intensity is sufficiently low. The middle of the valence band is formed by gallium 3d states with oxygen 2s states lying below them. These states are hybridized with 4p states of gallium and germanium because of which there are Kβ′′-satellites in the Kβ2-subbands of gallium and germanium. The bottom of the valence band is formed by 3d states of germanium, whose contribution to chemical bonding is insignificant. The X-ray emission bands of Ga and Ge in Ca3Ga2Ge4O14 and the photoelectron spectrum of the valence electrons of Ca3Ga2Ge4O14 are in good agreement. The OKα-band changes its fine structure only slightly upon doping Ca3Ga2Ge4O14 with Ce or Eu. The investigations of intrinsic luminescence under X-rays excitation of Ca3Ga2Ge4O14 gallogermanate are presented. [ABSTRACT FROM AUTHOR]

Gallium oxide has recently been identified as a promising scintillator. To assess its potential as a detector material for ionizing radiation at low temperatures, we measured the luminescence and scintillation properties of an undoped Ga2O3 crystal over the 7–295 K temperature range. The emission of the crystal is due to the radiative decay of self-trapped excitons and donor-acceptor pairs and peaks at a wavelength of 380 nm. The scintillation light output of the undoped Ga2O3 increases with a decrease in temperature, reaching a maximum value of 19 300 ± 2200 ph/MeV at 50 K. The measured luminescence kinetics has a recombination character with specific decay time (τ0.1) increasing from 1 to 1.8 μs at cooling. Since radiative decay in the crystal competes with nonradiative processes, material optimization could lead to the scintillator achieving a yield of 40800 ph/MeV, a figure considered to be an upper limit. [ABSTRACT FROM AUTHOR]