Large energy resolution improvement of LYSO scintillator by electron beam lithography method

Abstract

A (Lu,Y)2SiO5:Ce (LYSO) crystal, as a heavy inorganic scintillator, is currently in high demand for various applications in the fields of particle detection. However, its high refractive index (n = 1.83) gives restriction on the measurements of rare events or weak particle flow, where high energy resolution is urgently required for detectors based on the crystal. Utilizing the electron beam lithography technique and the ion beam lithography method, we have successfully prepared a 2.0 × 2.0 mm2 large area two-dimensional photonic crystal (PhC) structure on the LYSO crystal surface. Compared with the plain reference sample, the optical measurements show a 53% enhancement of light extraction for the LYSO nanostructured surface, and the resulted improvement of energy resolution (full width at half maximum) is measured to be 43.8% by gaussian fittings to the energy spectra excited by the 241Am α source. With the advantage of high-resolution patterning, high thermal stability, and firm stickiness on the substrate, the present prescription of the PhC fabrication is still favorable for some special fields (e.g., homeland security and space exploration) though the writing process is extremely time consuming and expensive to use.

Light Extraction Enhancement Techniques for Inorganic Scintillators

“…Indeed, from measurements performed on our air-coupled samples with Teflon wrapping we observed an improvement of ∼25% and ∼15% in energy resolution and ∼50% and ∼30% in light gain for LYSO and BGO, respectively. In this case, the gain provided by the PhC coating, without employing optical coupling compounds, was in line with what reported in the literature [17][18][19][20][21][22]26].…”

“…These structures rely on a high refractive index contrast between the nanostructure and the surrounding medium, leading to interesting optical properties especially if applied on the surface of high refractive index material. Indeed, PhCs have shown to be capable of increasing the amount of light extracted from inorganic scintillators, albeit to varying degrees and under often quite different experimental conditions, such as for LSO [17], LYSO [19][20][21][22] (self-assembly and e-beam, and nanoimprint), GYGAG and SrI 2 [23] (nanoimprint), CsI(Na) [24,25], and BGO [26] (self-assembly). A more comprehensive description of the PhC physics is reported in [17,18].…”

Bright Innovations: Review of Next-Generation Advances in Scintillator Engineering

“…Gain in the measured light signal is reported in the articles cited here, and we have used the terminology “light output” for it. The following observations could be made based on Table : The significant variation of light output was seen even with the similar combinations of a scintillator and a dielectric PhC, having different dimensions of the nanostructure, e.g., The light output of LYSO coated with TiO 2 PhC increases by 53% and up to 70% in the 2D pattern of air holes of different sizes engraved on TiO 2 . The light output of LYSO coated with a monolayer of polystyrene nanospheres varies from 38% to 220%, depending on the size of the nanospheres. , PhCs with higher RI materials lead to stronger scattering amplitudes, therefore, more light extraction and brighter diffraction orders, e.g., gain in light output by 50% and 40% and energy resolution by 9% and 3.6% when GYGAG nanoimprinted with polymers with RI 1.875 and 1.825, respectively Similarly, the deposition of an additional layer of a higher refractive index, e.g., TiO 2 , is an additional way to fine-tune a photonic layer, e.g., light output increases by 33% and 101.6% in BGO/PMMA ( n = 1.5) and BGO/PMMA ( n = 1.5)/TiO 2 ( n = 2.5) scintillator …”

“…Gain in the measured light signal is reported in the articles cited here, and we have used the terminology "light output" for it. The following observations could be made based on Table 2: (a) The significant variation of light output was seen even with the similar combinations of a scintillator and a dielectric PhC, having different dimensions of the nanostructure, e.g., (i) The light output of LYSO coated with TiO 2 PhC increases by 53% 55 and up to 70% 56 in the 2D pattern of air holes of different sizes engraved on TiO 2 . (ii) The light output of LYSO coated with a monolayer of polystyrene nanospheres varies from 38% to 220%, depending on the size of the nanospheres.…”

Optimization of WLS fiber readout for the HERD calorimeter

“…Titanium oxide, another common highly reflective material, was not included in this measurement due to its signal amplitude being only 50% of the ESR film coating found in previous HERD prototype [12]. Many micro-structure machining techniques have been utilized to modify the surfaces of scintillator, demonstrating their potential in enhancing light output [13][14][15]. However, practical application remains challenging due to processing complexity and inefficiency at this stage.…”