Scintillators can absorb high-energy rays or particles (X-ray or
Chinese Optics Letters, Volume. 21, Issue 7, 071601(2023)
Tb3+-doped borosilicate glass scintillators for high-resolution X-ray imaging
Scintillators are the vital component in X-ray perspective image technology that is applied in medical imaging, industrial nondestructive testing, and safety testing. But the high cost and small size of single-crystal commercialized scintillators limit their practical application. Here, a series of Tb3+-doped borosilicate glass (BSG) scintillators with big production size, low cost, and high spatial resolution are designed and fabricated. The structural, photoluminescent, and scintillant properties are systematically investigated. Benefiting from excellent transmittance (87% at 600 nm), high interquantum efficiency (60.7%), and high X-ray excited luminescence (217% of Bi4Ge3O12), the optimal sample shows superhigh spatial resolution (exceeding 20 lp/mm). This research suggests that Tb3+-doped BSG scintillators have potential applications in the static X-ray imaging field.
1. Introduction
Scintillators can absorb high-energy rays or particles (X-ray or
Silicate glass has the advantages of high heat resistance, high mechanical strength, and excellent physical-chemical stability, but it also has a high melting temperature[18,19,25]. The addition of boron oxide can effectively reduce the melting temperature, and the resulting phase separation phenomenon can be solved by adding sodium oxide. The addition of alumina can form aluminum–oxygen tetrahedrons in glass and bridge the glass network, which closes the glass structure and improves performance. The addition of barium oxide can effectively introduce heavy element barium to improve the radiation resistance and absorption of X rays. Such borosilicate glass (BSG), combined with a glass network intermediate (alumina) and glass network extras (sodium oxide and barium oxide), may present good scintillating properties in the X-ray imaging field after being activated by the appropriate REI.
Among the REI,
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In this work, the BSG with the addition of alumina, sodium oxide, and barium oxide were designed and fabricated as the glass host for
2. Experiment
2.1. Specimen preparation
Glass specimens were produced via conventional melt-quenching on the basis of a specific constituent of (mole fraction)
2.2. Sample characterization
X-ray diffraction (XRD) patterns were analyzed utilizing an X-ray apparatus (MiniFlex/600, Rigaku) with a
The static X-ray imaging system includes an X-ray source, imaging objects, scintillator sample, and optical camera. A Mini-X X-ray tube (Amptek) with Ag target was selected as the X-ray source (the input voltage is maintained at 50 kV, and the input current can be adjusted in the 5–79 µA range). An X ray partially absorbed by an imaging object (such as an encapsulated chip, ballpoint pen, or standard X-ray test pattern plate) was projected onto the scintillator glass; the resulting radiative luminescence is refracted through a prism and captured and recorded by an sCMOS camera (Teledyne Photometrics) to form X-ray images.
3. Results and Discussion
3.1. Structural properties
Figure 1(a) depicts the XRD patterns of all specimens. All samples only show diffraction humps without diffraction peaks, which means that all samples are glassy. Figure 1(b) exhibits the FT-IR spectra of G-host and G-6Tb specimens. The absorption at about
Figure 1.(a) XRD patterns of all specimens; (b) FT-IR spectra of G-host and G-6Tb specimens.
Density (
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The transmittance of the scintillator is an important factor that affects the spatial resolution of an X-ray imaging system. The transmittance spectra of all specimens are presented in Fig. 2(a). All specimens show good transmittance, whose value is about 87%@600 nm. The absorption peaks situated at 340, 352, 368, 378, and 484 correspond to the emblematic transition of
Figure 2.(a) Transmittance spectra of all samples; (b) relationship between α2 and hν for G-host and G-6Tb samples.
The photographs of all samples are displayed in Fig. 3. In the sunlight, all samples appear very transparent. The high transparency of samples allows the printed font to be clearly seen through the sample. And under the excitation of 365 nm light, G-xTb specimens present typical green emission of
Figure 3.Photos of all samples (a) under daylight and (b) under 365 nm light irradiation.
3.2. Photoluminescent properties
Figure 4(a) demonstrates the PL spectra (
Figure 4.(a) PL spectra (λex = 378 nm) of all samples; (b) PLE spectra (λem = 542 nm) of all samples.
IQE values of the G-xTb specimens were gauged and calculated, as demonstrated in Fig. 5(a). The values of IQE enumerated in Table 2 can be computed by utilizing the following formula[41,42]:
Figure 5.(a) IQE spectra of G-xTb specimens; (b) decay curves (λex = 378 nm) of 542 nm emission of G-xTb specimens.
The luminescence decay curves (
3.3. Radioluminescent properties and X-ray imaging
To characterize the scintillating capability of G-xTb specimens in X-ray imaging, Fig. 6(a) shows the XEL spectra of commercial BGO crystal and G-xTb specimens. As the
Figure 6.(a) XEL spectra of BGO crystal and G-xTb specimens; (b) relationship between XEL intensity and X-ray dose rate.
The ratio of the integrated XEL intensity between G-xTb samples and BGO is calculated and listed in Table 2. Notably, the XEL intensity of the G-6Tb specimen reaches 217% of that of BGO. It suggests that the G-6Tb sample might have a potential application in X-ray imaging. The relationship between XEL intensity and the X-ray dose rate of the G-6Tb sample is displayed in Fig. 6(b). These experimental data points match well (
The X-ray imaging capacity was investigated by a suborbicular G-6Tb optimal sample with
Figure 7.Photos of G-6Tb sample for (a) X-ray imaging, (c) encapsulated chip, (e) ballpoint pen, and (g) standard X-ray test pattern plate; X-ray images of (b) sample, (d) encapsulated chip, (f) ballpoint pen, and (h) standard X-ray test pattern plate.
The spatial resolution is one of the most important parameters for X-ray imaging. It can be obtained in the image of a standard X-ray test pattern plate [photo in Fig. 7(g)], shown in Fig. 7(h). The image distinctly shows that six light lines can be resolved, even at densities over 20 lp/mm, indicating that the optimal sample presents superhigh spatial resolution (exceeding 20 lp/mm). Such high spatial resolution can meet the requirements of actual X-ray imaging. For a better comparison, the spatial resolution values of some different scintillating materials for X-ray imaging are listed in Table 3. The spatial resolution of the G-6Tb sample reaches the highest level. In brief,
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Figure 8 illustrates the mechanism of
Figure 8.Mechanism of Tb3+-doped BSG scintillators.
In the measurement of XEL spectra, the color of the G-6Tb sample changes from colorless to slightly yellow, indicating that X-ray irradiation will cause damage to glass. Figure 9(a) shows the transmittance spectra of the G-6Tb sample irradiated by an X ray with different input powers for 5 min. It is clear that the transparency at 320–550 nm decreases with the increase of input power. For a better comparison and to explain the color change mechanism, the transmittance spectra of the G-6Tb sample before irradiation, after X-ray irradiation (10 W), and their difference are displayed in Fig. 9(b). A broad absorption band at around 320–550 nm is observed, which can corresponde to the charge change absorption of
Figure 9.(a) Transmittance spectra of G-6Tb sample before radiation, after being irradiated by X rays with different input powers for 5 min, and after subsequent heat treatment; inset (i) is photo of G-6Tb sample after X-ray irradiation (10 W, A-I) and inset (ii) is photo of G-6Tb sample after subsequent heat treatment (H-T); (b) transmittance spectra of G-6Tb sample before irradiation, after X-ray irradiation (10 W), and their difference.
Inset (i) is the photo of the G-6Tb specimen after 10 W of X-ray irradiation. Inset (ii) displays the photograph of the G-6Tb specimen after subsequent heat treatment (300°C for 3 h). Combined with the transmittance curve after heat treatment in Fig. 9(a), it is interesting to note that the slightly yellow absorption from
The effect of irradiation time on XEL intensity was investigated. The XEL spectra and relative intensity curve of the G-6Tb specimen with continuous long-time X-ray irradiation (7 W) are shown in Figs. 10(a) and 10(b). With increasing irradiation time, the G-6Tb sample exhibits good irradiation luminescence stability. Only slight changes occur. The corresponding transmittance spectra of the G-6Tb sample before irradiation, after 100 min of X-ray irradiation, and their difference are displayed in Fig. 10(c). Similar to Fig. 9(c), their difference curves also exhibit absorption bands from
Figure 10.(a) XEL spectra of G-6Tb specimen with different X-ray irradiation time (7 W); (b) relative XEL intensity of G-6Tb sample after different irradiation time; (c) transmittance spectra of G-6Tb sample before irradiation, after 100 min X-ray irradiation, and their difference.
4. Conclusions
A battery of highly transparent BSG scintillators for X-ray imaging were devised and manufactured by melt-quenching technology. The transmittance of all specimens is about 87% at 600 nm, and the
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Wenjun Huang, Junyu Chen, Yi Li, Yueyue Wu, Lianjie Li, Liping Chen, Hai Guo, "Tb3+-doped borosilicate glass scintillators for high-resolution X-ray imaging," Chin. Opt. Lett. 21, 071601 (2023)
Category: Optical Materials
Received: Jan. 19, 2023
Accepted: Apr. 13, 2023
Published Online: Jul. 26, 2023
The Author Email: Hai Guo (ghh@zjnu.cn)