Scintillation materials and detectors that are used in many applications, such as medical imaging, security, oil-logging, high energy physics and non-destructive inspection, are reviewed. The fundamental physics understood today is explained, and common scintillators and scintillation detectors are introduced. The properties explained here are light yield, energy non-proportionality, emission wavelength, energy resolution, decay time, effective atomic number and timing resolution. For further understanding, the emission mechanisms of scintillator materials are also introduced. Furthermore, unresolved problems in scintillation phenomenon are considered, and my recent interpretations are discussed. These topics include positive hysteresis, the co-doping of non-luminescent ions, the introduction of an aimed impurity phase, the excitation density effect and the complementary relationship between scintillators and storage phosphors.

https://www.jstage.jst.go.jp/article/pjab/94/2/94_PJA9402B-02/_pdf

Inorganic scintillating materials and scintillation detectors.

Vacuum-Ultraviolet Photon Detections.

The luminescence and scintillation properties of ZnO single crystals were studied by photoluminescence and X-ray-induced luminescence (XRIL) techniques. XRIL allowed a direct comparison to be made between the near-band emission (NBE) and trap emissions providing insight into the carrier recombination efficiency in the ZnO crystals. It also provided bulk luminescence measurements that were not affected by surface states. The origin of a green emission, the dominant trap emission in ZnO, was then investigated by gamma-induced positron spectroscopy (GIPS) - a unique defect spectroscopy method that enables positron lifetime measurements to be made for a sample without contributions from positron annihilation in the source materials. The measurements showed a single positron decay curve with a 175 ps lifetime component that was attributed to Zn vacancies passivated by hydrogen. Both oxygen vacancies and hydrogen-decorated Zn vacancies were suggested to contribute to the green emission. By combining scintillation measurements with XRIL, the fast scintillation in ZnO crystals was found to be strongly correlated with the ratio between the defect luminescence and NBE. This study reports the first application of GIPS to semiconductors, and it reveals the great benefits of the XRIL technique for the study of emission and scintillation properties of materials.

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ZnO Luminescence and scintillation studied via photoexcitation, X-ray excitation, and gamma-induced positron spectroscopy.

Nonlinear optical response of bulk ZnO crystals with different content of intrinsic defects

The pulse radiation detectors are sorely needed in the fields of nuclear reaction monitoring, material analysis, astronomy study, spacecraft navigation, and space communication. In this work, we demonstrate a nanosecond X-ray detector based on ZnO single crystal semiconductor, which emerges as a promising compound-semiconductor radiation detection material for its high radiation tolerance and advanced large-size bulk crystal growth technique. The resistivity of the ZnO single crystal is as high as 1013 Ω cm due to the compensation of the donor defects (VO) and acceptor defects (VZn and Oi) after high temperature annealing in oxygen. The photoconductive X-ray detector was fabricated using the high resistivity ZnO single crystal. The rise time and fall time of the detector to a 10 ps pulse electron beam are 0.8 ns and 3.3 ns, respectively, indicating great potential for ultrafast X-ray detection applications.

Nanosecond X-ray detector based on high resistivity ZnO single crystal semiconductor

Single crystal bulk ZnO scintillator grown by the hydrothermal method was tested on its scintillation performances. In X-ray induced radio luminescence spectrum, it exhibited two intense emission peaks at 400 and 550 nm. The former was ascribed to the free and bound exciton related luminescence and the latter to oxygen vacancy related one, respectively. X-ray induced scintillation decay time of the exciton related emission measured by the pulse X-ray streak camera system resulted ∼ 4 ns. Finally, the light yield under 241Am 5.5 MeV α-ray was examined and it resulted ∼ 500 ph/5.5 MeV-α.(© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Optical and scintillation properties of bulk ZnO crystal

Response-time-improved ZnO scintillator by impurity doping

We report an over one-order-of magnitude improvement in the response time of conventional hydrothermal method-grown zinc oxide (ZnO) scintillator by introducing additional quenching channels via intentional indium ion doping. A 3-ps fluorescence decay time constant is achieved, therefore making it the fastest scintillator operating below 100 nm to date. Using this indium-doped ZnO, relative jitter between extreme ultraviolet free electron laser (EUV-FEL) probe and optical pump pulses is evaluated to be less than 3 ps. Moreover, pulses from these sources can be synchronized with 3-ps accuracy through in-situ observation of relative time difference in single-shot base.

https://iopscience.iop.org/article/10.1143/APEX.4.062701/pdf

Response Time-Shortened Zinc Oxide Scintillator for Accurate Single-Shot Synchronization of Extreme Ultraviolet Free-Electron Laser and Short-Pulse Laser

High quality In-doped ZnO single crystal was grown using the hydrothermal method. The growth rate for both ; and ; directions is about 80 μm/day. The X-ray rocking curve (XRC) full width at half maximum (FWHM) of the (0002) reflection is 24.2 arcsec. In order to make it possible to use this material as a scintillator for in situ imaging of soft X-ray laser with high spatial resolution, we prepared an In-doped ZnO wafer (9.0 mm x 9.0 mm x 0.75 mm) and mounted it on a vacuum flange. The decay time constant is evaluated to be 120 ps, therefore making it an ideal scintillator for in situ imaging device of soft X-ray laser with high spatial resolution. Furthermore, In-doped ZnO scintillator with such short decay time constant is suitable for high accuracy alignment and synchronization of ultrafast, short wavelength laser sources for pump-and-probe experiments.

Fabrication of In-Doped ZnO Scintillator Mounted on a Vacuum Flange

A scintillator material is made of a zinc-oxide single crystal grown on a +C surface or a −C surface of a plate-shaped seed crystal of zinc oxide including a C surface as a main surface. The zinc-oxide single crystal contains In and Li. In response to an incident radiation, the scintillator material emits fluorescence of less than 20-ps fluorescence lifetime.

Akira Wakamiya

Papers

Optical and scintillation properties of bulk ZnO crystal

Response-time-improved ZnO scintillator by impurity doping

Response Time-Shortened Zinc Oxide Scintillator for Accurate Single-Shot Synchronization of Extreme Ultraviolet Free-Electron Laser and Short-Pulse Laser

Fabrication of In-Doped ZnO Scintillator Mounted on a Vacuum Flange

Scintillator material and scintillation detector