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Description
Zinc oxide has a variety of practical applications due to its unique properties. In particular, high radiation hardness and the presence of an ultrafast emission component make this material prospective for scintillators [1]. As a rule, various forms of ZnO exhibit two luminescence bands. One of them is a narrow UV band located near the absorption edge of the crystal; therefore it is called near-band-edge (NBE) emission. Another one is a broad band, its maximum usually placed in the green spectral range, this luminescence with decay time in microsecond range is associated with deep-level (DL) emission. It is known that the introduction of elements of group III: In or Ga in ZnO leads to an increase in the intensity of fast NBE luminescence and reduction in the intensity of the slow component [1].
This work presents the results of the complex study of ZnO, ZnO:Ga and ZnO:In scintillation ceramics which were prepared by hot uniaxial pressing technique [2].
The obtained ZnO ceramics with thickness of 0.5 mm show the total transmittance of 55% at 550 nm wavelength, which is a rather high value for ceramics based on a material possessing a hexagonal structure. The transmittance of ZnO:In and ZnO:Ga ceramics reaches maximum near 500 nm and then begins to drop with wavelength. Increase in the dopant concentration leads to growth of absorption in long-wavelength spectral range due to creation of large amount of donor centers. Maximum value of transparency in total transmittance spectra is determined by average grain size: the finer the grain the smaller the total transmittance.
Reflectance spectra of the ceramics have been measured in the IR range to estimate concentration of free charge carriers. Minima of the spectral reflectance are located at 14.90, 3.75 and 6.88 um for ZnO, ZnO:Ga and ZnO:In, respectively. As expected, the free charge carriers concentration in ZnO:In(0.1 wt.%) (n=1.53×1019 cm–3) and ZnO:Ga(0.1 wt.%) (n=3.439×1019 cm–3) is much higher than that in ZnO ceramics (n=3.26×1018 cm–3). Measurements of radioluminescence spectra show that introduction of indium or gallium suppresses the DL band and increases the intensity of the NBE band (peaking at the 388.3 and 389.6 nm for In and Ga, respectively). Maximum of NBE luminescence intensity is reached at dopant concentration 0.13 wt.% and 0.05 wt.% for ZnO:In and ZnO:Ga, respectively. Radioluminescence decay curves of the ceramics have been studied. The main decay constant of the ZnO:In(0.13 wt.%) ceramics is 0.7 ns. Annealing of the ZnO:Ga and ZnO:In ceramics in the Ar:H2 atmosphere allowed to increase the light yield of the fast component by ~ 6 times. Physical processes responsible for luminescence kinetic and spectral properties of the studied ceramics are discussed.
References
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299, 458 (1990). - P. Rodnyi, K. Chernenko, O. Klimova et al. Rad. Measurements. 90,
136 (2016).
