Xiaoping Ouyang

Guided-mode resonance assisted directional emission of a wavelength-shifting film for application in scintillation detection

Thin-film luminescent layers as wavelength shifters using in the scintillation detection system suffer with low efficiency due to the total internal reflection and the non-directional emission. In the present work, we design and fabricate a photonic crystal on the surface of LuTaO(4):Eu(3+) thin-film which is a newly developed luminescent material using in radiation detection systems. The entire structure shows guided-mode resonances with only one TE and TM mode. As a result, the emitting light is effectively extracted. Furthermore, due to only two modes existing in the layer, the directionality of emission is strongly controlled. This result enables the structured LuTaO(4):Eu(3+) thin-film to be a potential wavelength shifter with high-efficiency.

Scaling-induced enhancement of X-ray luminescence in CsI(Na) crystals

We report on the diameter dependence luminescence property of CsI(Na) crystals under X-ray excitation. When CsI(Na) crystal diameter decreases to nano-scale, the X-ray excited luminescence decay time is speeding up from ∼600u2009ns to ∼10u2009ns and 420u2009nm Na-related cathodeluminescence is affected drastically. The reason is confirmed that diameter reduction leads surface effect to accelerate the excitons quenching. These measurement results identify a critical distinguished boundary ∼20u2009μm) of crystal diameter, which provide a new way to potential application of CsI(Na) crystals in the development of fast X-ray and gamma scintillator film detectors with large area.

Enhancement of directional broadband luminescence from a scintillation film via guided-mode resonance in a photonic crystal structure

Scintillation films play an important role in radiation detection. Improved light output and control of emission directionality are critical for practical applications. To obtain enhancement of broadband directional luminescence from a Lu2SiO5:Ce3+ scintillation film, a special photonic crystal structure is deposited on the film surface to provide multiple guided-mode resonances. The structure can be designed according to the application requirements. Numerical simulations are performed to analyze the enhancement. Overall, this method could be used when directional emission is required for radiation detection.

The luminescence characteristics of CsI(Na) crystal under α and X/γ excitation

In this paper, we study the effective decay time characteristic of CsI(Na) crystal under 239Pu alpha particle and 137Cs gamma-ray excitation using a single photon counting decay time measurement system. The measurement system employs a silicon optical fiber to couple and transit single photon. The slow decay time component of CsI(Na) crystal is 460–550u2009ns. We observe a 15u2009ns fast decay component under alpha particle excitation. In addition, we find that the primary stage of the falling edge in the decay time curve is non-exponential and drops rapidly when CsI(Na) crystal is excited by 239Pu alpha particles. Since the high density of self-trapped-excitons (STEs) is produced in alpha particle excitation process, we propose that the fast falling edge is corresponding to the quenching process of STEs which transit with non-radiation in the case of high excitation density. To prove this proposal, we excited the CsI(Na) crystal with sub-nanosecond intensive pulsed X-ray radiation. Our X-ray impinging results sh...

Modified timing characteristic of a scintillation detection system with photonic crystal structures

It is intuitively expected that an enhanced light extraction of a scintillator can be easily achieved by photonic crystal structures. Here, we demonstrate a modified timing characteristic for a detection system induced by enhanced light extraction with photonic crystal structures. Such improvement is due to the enhanced light extraction which can be clearly proven by the independent measurements of the light output and the timing resolution. The present investigation is advantageous to promote the development of a scintillation detection system performance based on the time-of-flight measurement.

Plasmonic lattice resonance-enhanced light emission from plastic scintillators by periodical Ag nanoparticle arrays

We have demonstrated that periodical arrays of silver nanoparticles can enhance the light emission from a plastic scintillator layer on the surface of a silicon substrate. The enhancement is attributed to surface lattice resonances with a photonic-plasmonic nature. Although the enhancement exhibits directional characteristics for individual wavelengths, the wavelength-integrated enhancement shows a monotonous increase with increasing emission angle. As a result, an overall 1.81-fold wavelength- and angle-integrated enhancement has been obtained. This observation is promising for fundamental and applied research into enhanced luminescent material layers on opaque substrates.

Directional emission of quantum dot scintillators controlled by photonic crystals

We have demonstrated enhanced light emission from a CdSe/ZnS quantum dot scintillator film in the normal direction by photonic crystal structures. With the control of the photonic crystal structures, a two-fold enhancement was achieved for the wavelength-integrated emission spectra under the excitation of both ultra-violet and X-rays, which is beneficial to radiation detection applications. Furthermore, it is found that the optical properties such as the bandwidth and peak wavelength can be controlled by adjusting the thickness of a TiO2 conformal layer which was deposited on the surface of the photonic crystal slab formed from solidified resist.

A theoretical and experimental research on detection efficiency of HPGe detector for disc source with heterogeneous distribution

If we treat some heterogeneous distributed media including heterogeneous distributed radioactive sources, radioactive polluted field, “hot point/hot area” and “hot particle” as uniform distributed media, directly affects the accuracy of the detection efficiency calibrated, introduced the great metrical deviation. A Standard Normal distribution disc source was simulated by a point source experiment. The detection efficiency of heterogeneous distributed disc source is defined as multiply efficiency function of point source by the probability density function. And then we carried out process of the mathematical integrality and normalization. A description of the analysis and experimental results of this method are presented. The theoretical and experimental calculation of detection efficiency of HPGe detector for heterogeneous distribution disc source is consistent with each other.

Recoil-proton track imaging as a new way for neutron spectrometry measurements

Recoil-proton track imaging (RPTI) is an attractive technique to optically record the tracks of recoil protons in scintillation gas by using realtime imaging devices. For the first time, its use as an online nuclear track detector for neutron spectrometry measurements (NSM) is explored. Based on the RPTI methodology for NSM, a very basic detector system is designed, consisting of the neutron-to-proton recoil system and proton track imaging system. Satisfactory performance of the RPTI neutron spectrometer has been examined with a series of Monte Carlo simulations. Moreover, using well-defined line-proton sources from a tandem accelerator, the capability of the detector for imaging proton tracks at the single-particle level in real time has been validated in preliminary experiments. From the clear single proton tracks in the images, the proton ranges were easily distinguished, and precise proton energy spectra were unfolded, laying a solid experimental foundation for the future implementation of NSM.

Directional emission of plastic luminescent films using photonic crystals fabricated by soft-X-ray interference lithography and reactive ion etching

In this report, a novel method to prepare photonic crystals based on the combination of soft-X-ray interference lithography (XIL) and reactive ion etching (RIE) with a bi-layer photoresist system was developed. XIL can be utilized to prepare periodic structures with high efficiency but the depth of etch is limited due to the strong absorption of photoresist for soft-X-ray. Based on the pattern prepared by XIL, RIE can be utilized to further etch a second layer of photoresist, so that one can obtain a large depth of etch. Controlling the dispersion relation of the prepared photonic crystals, strongly directional emission of plastic luminescent films was demonstrated. A wavelength-integrated enhancement of 2.64-folds enhancement in the range of 420 to 440u2009nm in the normal direction was obtained. Guided-mode resonance and Fabry-Perot resonance could be the critical factors to control the directional emission. Devices based on directional emission films have a variety of applications in such as detectors, optical communication and display screens.