An efficient Cu⁺ doped Gd-based fluoroaluminosilicate scintillator glass for X-ray detectors

Abstract

Glass scintillators possess several advantages compared to single crystals and ceramics, including easy manufacturing, low cost and excellent physicochemical stability. However, the X-ray excited luminescence (XEL) intensity and spatial resolution of glass scintillators need to be further improved. In this paper, in order to improve the scintillating and luminescence properties of Cu⁺ doped glass scintillators, a series of strategies have been adopted. Firstly, Al reducing agent is introduced to inhibit the production of Cu²⁺. Secondly, energy transfer strategy is realized by adding Gd³⁺ sensitizer. Finally, fluoroaluminosilicate glass is selected as glass host to improve the transparency. High transmittance (80.4%@547 nm), extremely high X-ray attenuation efficiency (99.99%@2 mm), excellent integrated XEL intensity (176% of that of Bi₄Ge₃O₁₂) and outstanding spatial resolution (20 lp mm⁻¹) suggest that Cu⁺ doped fluoroaluminosilicate glass may be used in X-ray monitoring and imaging.

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1. Introduction

Scintillator materials have important applications in many fields, such as medical diagnosis, national defense and nuclear technology.^1,2 They can convert high energy X-ray photons into low energy visible light for X-ray monitoring and imaging.^3–5 At present, common scintillator materials are single crystals, ceramics and glasses. Even though single crystals and ceramics possess outstanding scintillating properties, they have the disadvantages of high cost, complex manufacturing processes, difficulty in producing large-sizes and time-consuming production.⁶ In contrast, glass materials attract researchers’ attention because of their advantages of low cost, simple manufacturing technology, convenience of fabricating in large sizes and feasibility of industrial production.^3,7,8

High spatial resolution and X-ray excited luminescence (XEL) intensity are indispensable for high-performance scintillators for X-ray imaging. Therefore, it is urgent to search for activator-doped glass materials with high spatial resolution and high XEL intensity.

The choice of an activator is critical. Rare earth ions such as Tb³⁺, Eu³⁺ and Dy³⁺ are usually used as activators in glass scintillators. They exhibit narrow band emission and fixed emission peaks because of f–f transition. Their fluorescence lifetime is in the order of milliseconds. For dynamic X-ray imaging, ions with short lifetimes like Ce³⁺, Eu²⁺ and Cu⁺ are needed. The lifetime of Cu⁺ is in the microseconds range. Compared with Eu²⁺ and Ce³⁺, Cu⁺ has the advantages of high efficiency, low price and security. In addition, Cu⁺ has wideband blue emission, which comes from the 3d⁹ 4s¹ → 3d¹⁰ transition.^9–12 The visible luminescence of Cu⁺ is consistent with the spectral sensitivity of ordinary photoelectric detector.¹³ Consequently, Cu⁺ doped scintillators may have broad application prospects in X-ray imaging and high-energy radiation detection. For example, many groups have reported perovskite scintillators containing Cu⁺ for X-ray imaging.^13,14 Recently, Liu et al. prepared a Cs₃Cu₂I₅@PMMA scintillator film for X-ray imaging with a spatial resolution of 20 lp mm⁻¹.¹⁵

Three strategies were used to improve the scintillating and luminescent properties of Cu⁺ doped glass. The first one is to use Al powder as reducing agent to control the oxidation of Cu⁺ to Cu²⁺.^16,17 Cu exists in amorphous glass in various valence states (mainly as Cu nanoparticles (NPs), Cu⁺, and Cu²⁺).¹⁸ In melting process, when Al content is superfluous, Cu NPs will be produced as Cu⁺ is reduced, and when Al content is lacking, Cu²⁺ will be produced as Cu⁺ is oxidized.¹⁶ Both will lead to a decrease in the transmittance and XEL intensity of glass.¹⁹ Therefore, it is necessary to control the contents of Cu⁺ and Al accurately to obtain the best comprehensive performance.

The second one is to introduce suitable sensitizer. Gd³⁺ is an excellent luminescent sensitizer, which has an atomic number of 64 and has strong X-ray attenuation.²⁰ The ⁶P_J (J = 3/2, 5/2, 7/2) of Gd³⁺ is close to the ³T_2g of Cu⁺, which is conducive to the energy transfer (ET) of Gd³⁺ → Cu⁺.

The third one is to employ oxyfluoride glass host. Fluoroaluminosilicate glass, a kind of oxyfluoride glass, was selected as host material due to its high mechanical strength, high thermal stability, high chemical stability and low phonon energy environment for activator ions.^21–25 The fluoroaluminosilicate glass possesses high transparency.

In this work, the luminescent and scintillating properties of Cu⁺ doped 70SiO₂–7Al₂O₃–16SrF₂–7GdF₃ glass were investigated using the above three strategies. The optimal glass has excellent transmittance (80.4%@547 nm) and high XEL intensity (176% of that of Bi₄Ge₃O₁₂ (BGO)). High spatial resolution (20 lp mm⁻¹) is presented when applied in X-ray imaging. These results suggest that the optimal glass may be used as a scintillator in the field of X-ray imaging.

2. Experimental

A series of Cu⁺ doped glass scintillators were prepared using melt quenching method. The components of glasses are based on 70SiO₂–7Al₂O₃–16SrF₂–7GdF₃–xCu₂O–yAl (x = 0.05, 0.1, 0.15, 0.2, 0.25, and 0.3; y = 0.5, 0.55, 0.58, and 0.60, in mol ratio). As listed in Table 1, the host without any doping was named G-host, and the glass samples doped with xCu₂O and yAl were named GCuXAlY (X = 20x, Y = 10y). Part A in the ESI† file provides details on the preparation of glass samples and characterization of their structural, luminescent and scintillating properties.

Table 1 The contents of Cu₂O and Al in the GCuXAlY sample, as well as their transmittance at 547 nm and integrated XEL intensity (I_XEL, compared to BGO)

Sample	Cu2O	Al	Transmittance (%)	I XEL (%)
G-host	0	0	44.6	—
GCu1Al5.5	0.05	0.55	61.3	65
GCu2Al5.5	0.1	0.55	65.2	110
GCu3Al5.5	0.15	0.55	80.4	176
GCu4Al5.5	0.2	0.55	78.5	134
GCu5Al5.5	0.25	0.55	69.5	90
GCu6Al5.5	0.3	0.55	70.8	81
GCu3Al5	0.15	0.50	70.8	124
GCu3Al5.8	0.15	0.58	78.4	149
GCu3Al6	0.15	0.60	77.9	139

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3. Results and discussion

The X-ray diffraction (XRD) patterns of representative glass samples are shown in Fig. 1(a). The undoped G-host sample has obvious diffraction peaks. These peaks match well with the PDF standard card of SrF₂, suggesting the crystallization of SrF₂ nanocrystals in G-host sample. The XRD patterns of GCu5Al5.5, GCu3Al5.5 and GCu3Al6 samples show a hump shape without an obvious diffraction peak, indicating the amorphous phase of these glass samples. The introduction of Cu⁺ and Al inhibits the crystallization of SrF₂ nanocrystals.

Fig. 1 (a) XRD patterns of the GCu5Al5.5, GCu3Al5.5, GCu5Al6 and G-host samples and standard patterns of SrF₂ (PDF#88-2294). (b) FTIR spectra of GCu3Al5.5 and G-host samples. (c) Transmittance spectra of the GCuXAl5.5 and G-host samples. (d) Transmittance spectra of GCu3AlY and G-host samples.

Fig. 1(b) depicts the Fourier transform infrared spectroscopy (FTIR) spectra of G-host and GCu3Al5.5 samples. The FTIR spectra show a wide absorption band in the range of 400–1400 cm⁻¹. The strongest absorption band in 900–1100 cm⁻¹ region corresponds to the symmetric stretching vibration of Si–O–Si in the [SiO₄]⁴⁻ tetrahedron.^26,27 The characteristic absorption in the range of 700–780 cm⁻¹ is caused by the valence vibration of Al–O bond in [AlO₄]⁵⁻ tetrahedron.^26–28 The absorption band of 400–543 cm⁻¹ belongs to the flexural vibration of Si–O–Si and Si–O–Al bridge oxygen.^26–28 It is worth noting that absorption peaks of GCu3Al5.5 near 1100 cm⁻¹ and 700–780 cm⁻¹ shift to a lower wavenumber compared to G-host sample. This is due to the substitution of Si⁴⁺ by Al³⁺ with the doping of Al, which interferes with the main characteristics of Si–O tensile vibration.²⁹

Fig. 1(c) and (d) show the transmittance spectra of GCuXAlY and G-host samples. The wide absorption band of 600–800 nm belongs to characteristic Cu²⁺ absorption. The wide absorption band in the 270–340 nm UV region in Cu⁺ doped glass is assigned to the d¹⁰ → d⁹s (d → s) transition of Cu⁺.^9,10,16,30

In Fig. 1(c), G-host has a low transmittance because it contains SrF₂ nanocrystals. When the concentration of Cu⁺ is low (X < 3), the transmittance of glass samples increases with the rise of Cu⁺ concentration. When X = 3, the glass sample has the best transmittance. When Cu₂O is excessive (X > 3), the transmittance of the glass samples decreases because the concentration of Cu²⁺ increases and the absorption of Cu²⁺ becomes stronger.

In Fig. 1(d), when the concentration of Al is low (Y < 5.5), the absorption band of Cu²⁺ is obvious because the content of Al is insufficient to reduce Cu²⁺. When Y = 5.5, glass sample has the best transmittance. When the concentration of Al increases (Y > 5.5), the transmittance of glass samples decreases slightly because of a small excess of Al.

The transmittance of each glass sample at 547 nm is given in Table 1. GCu3Al5.5 has the highest transmittance above 80% at 400–800 nm.

As presented in Fig. S1 (ESI†), the energy gap (E_g) between the conduction band and valence band of G-host is calculated to be 3.95 eV.²⁸

Fig. 2(a) presents the photoluminescence excitation (PLE) spectra of GCuXAl5.5 samples detected at 446 nm emission. A wide excitation band peaked at 291 nm can be observed, which is a result of the d → s transition of Cu⁺.^9,10,16,30 In addition, the excitation peak at 313 nm comes from the ⁸S_7/2 → ⁶P_7/2 transition of Gd³⁺.^20,31,32 The excitation peak of Gd³⁺ suggests the existence of ET from Gd³⁺ to Cu⁺.

Fig. 2 (a) PLE (monitored at 446 nm) and PL spectra (excited by 291 nm) of GCuXAl5.5 samples. (b) PLE (monitored at 313 nm) and PL spectra (excited by 273 nm) of GCuXAl5.5 samples. (c) PLE (monitored at 446 nm) and PL spectra (excited by 273 nm) of GCu3Al5.5 sample. (d) Fluorescence decay curves of 313 nm emission (excited by 273 nm) of G-host and GCuXAl5.5 samples.

The photoluminescence (PL) spectra of GCuXAl5.5 samples under the excitation of 291 nm are displayed in Fig. 2(a). The wide blue emission band peaked at 446 nm corresponds to the d⁹s → d¹⁰ (s → d) transition of Cu⁺.^9,10,16,30 When X < 3, the PL and PLE intensity increase as more Cu²⁺ is reduced to Cu⁺. When X > 3, the PL and PLE intensity decreases due to concentration quenching. GCu3Al5.5 has the highest PL intensity.

The PLE spectra of the GCuXAl5.5 samples monitored at 313 nm are shown in Fig. 2(b). The main excitation peak at 273 nm corresponds to the ⁸S_7/2 → ⁶I_7/2 transition of Gd³⁺.³³ In PL spectra excited at 273 nm (Fig. 2(b)), a narrow peak with extremely high intensity appears at 313 nm, which comes from ⁶P_7/2 → ⁸S_7/2 of Gd³⁺.^20,31,32 The wide band peaked at 446 nm belongs to the characteristic transition of Cu⁺. With the increase of X, the PL and PLE intensity of Gd³⁺ decrease continuously, which is due to the ET of Gd³⁺ → Cu⁺. When X < 3, the PL intensity of Cu⁺ gradually increases, which is caused by increased Cu⁺ and the ET from Gd³⁺ to Cu⁺. When X > 3, the PL intensity of Cu⁺ decreases as a result of concentration quenching. GCu3Al5.5 has the highest PL intensity of Cu⁺. The overlap of PL spectra excited at 273 nm and PLE spectra monitored at 446 nm of GCu3Al5.5 sample in Fig. 2(c) demonstrates the ET of Gd³⁺ → Cu⁺.

Fig. 2(d) shows the fluorescence attenuation curves of 313 nm of GCuXAl5.5 (excited at 273 nm). The average lifetimes τ of the ⁶P_7/2 level of Gd³⁺ are presented in Fig. 2(d), which are calculated using the following formula,

where I(t) is the emission intensity at time t. The lifetime of ⁶P_7/2 level of Gd³⁺ decreases gradually with the rise of X. This confirms the ET of Gd³⁺ → Cu⁺.

The PLE spectra (λ_em = 446 nm) and PL spectra (λ_ex = 291 nm) of GCu3AlY samples are shown Fig. 3(a). In PLE spectra, the excitation band at 291 nm and excitation peak at 313 nm come from the d → s transition of Cu⁺ and the ⁸S_7/2→⁶P_7/2 transition of Gd³⁺, respectively. In PL spectra, the wide blue emission band peaked at 446 nm corresponds to the s → d transition of Cu⁺.

Fig. 3 (a) PLE (monitored at 446 nm) and PL spectra (emitted by 291 nm) of GCu3AlY samples. (b) PLE (monitored at 313 nm) and PL spectra (emitted by 273 nm) of GCu3AlY samples. (c) Fluorescence decay curves of 313 nm emission (λ_ex = 273 nm) of GCu3AlY samples. (d) Fluorescence decay curves of 446 nm emission (λ_ex = 291 nm) of GCu3Al5.5 samples.

When the concentration of Cu⁺ is constant and concentration of Al increases, the PL intensity of Cu⁺ first increases because Cu²⁺ is effectively reduced. Then PL intensity decreases due to concentration quenching. In order to further verify the reduction process, XPS spectra of GCu3Al5 and GCu3Al5.5 samples are given in part C of the ESI† file. The PL spectra indicate GCu3Al5.5 is optimal sample with the highest PL intensity.

Fig. 3(b) shows the PLE spectra (λ_em = 313 nm) and PL spectra (λ_ex = 273 nm) of GCu3AlY samples. In PLE spectra, the excitation peak at 273 nm corresponds to the ⁸S_7/2 → ⁶I_7/2 transition of Gd³⁺. In PL spectra, the narrow band at 313 nm and broad band at 446 nm come from the ⁶P_7/2 → ⁸S_7/2 transition of Gd³⁺ and the s → d transition of Cu⁺, respectively. The PL spectra indicate that GCu3Al5.5 is optimal sample with the highest PL intensity under 273 nm excitation.

The fluorescence attenuation curve of GCu3AlY monitored at 313 nm is displayed in Fig. 3(c). The τ values of ⁶P_7/2 of Gd³⁺ in GCu3Al5, GCu3Al5.5, GCu3Al5.8 and GCu3Al6 samples are 2.21, 2.69, 2.73 and 2.91 ms. Fig. 3(d) shows the fluorescence attenuation curve of the optimal sample GCu3Al5.5 monitored at 446 nm. The average lifetime of d⁹s of Cu⁺ is 40.35 μs.

PL spectra collected by integrating sphere are shown in Fig. S3(a) and (b) (ESI†). The calculation of internal quantum efficiency (IQE), external quantum efficiency (EQE) and absorption efficiency (Abs) values are given in part D in the ESI.† The IQE, EQE and Abs of the GCu3Al5.5 sample were obtained under 291 nm and 273 nm excitation. The IQE value of GCu3Al5.5 is 63.0% excited at 291 nm and 76.2% excited at 273 nm. The EQE value of GCu3Al5.5 is 55.3% excited at 291 nm and 66.7% excited at 273 nm. The Abs value of GCu3Al5.5 is 87.7% excited at 291 nm and 87.5% excited at 273 nm. The GCu3Al5.5 sample has high IQE, EQE and Abs, which symbolize that it might be a candidate for scintillator materials.

The excellent transparency, luminescent properties, wide band blue emission, short lifetime and high IQE all prove that Cu⁺ doped fluoroaluminosilicate glass might be an applicable scintillator for X-ray monitoring and imaging.

XEL intensity is one of important parameters to estimate the scintillating properties. Fig. 4(a) shows the XEL spectra of GCuXAl5.5 samples and BGO crystal. Fig. 4(b) shows the XEL spectra of GCu3AlY samples and BGO crystal. The emission band at 446 nm is attributed to the s → d transition of Cu⁺.¹¹ The characteristic emission peak at 313 nm is associated with the ⁶P_7/2 → ⁸S_7/2 transition of Gd³⁺. The XEL intensity of each glass sample is listed in Table 1 and Fig. 4(a) and (b).

Fig. 4 (a) XEL spectra of GCuXAl5.5 samples and BGO crystal. (b) XEL spectra of GCu3AlY samples and BGO crystal. (c) Attenuation coefficients of BGO, YAG:Ce,Si and GCu3Al5.5 at different photon energy states. (d) X-ray attenuation efficiency as a function of thickness. (e) XEL intensity of GCu3Al5.5 sample at different radiation times. (f) The relationship between radiation dose rate and XEL intensity of GCu3Al5.5 sample.

In Fig. 4(a), as X increases, the XEL intensity of Cu⁺ of GCuXAl5.5 significantly improves because of ET from Gd³⁺ to Cu⁺ and increased concentration of Cu⁺ (X < 3). The XEL intensity of Cu⁺ subsequently decreases due to the concentration quenching of Cu⁺ and increased concentration of Cu²⁺ (X > 3). The XEL intensity reaches the maximum value when X = 3. In Fig. 4(b), as Y increases, the XEL intensity of Cu⁺ of GCu3AlY first rises because of increased concentration of Cu⁺ (Y < 5.5) and then decreases due to concentration quenching of Cu⁺ (Y > 5.5). The XEL intensity reaches the maximum value when Y = 5.5. According to the above, GCu3Al5.5 sample has the highest XEL intensity.

The XEL intensity of GCu3Al5.5 is 176% of that of BGO. Compared with other scintillators listed in Table 2, GCu3Al5.5 sample displays outstanding XEL performance. Because the ET of Gd³⁺ → Cu⁺ is important in PL and XEL, the effect of Gd³⁺ concentration on XEL intensity was investigated and is shown in Fig. S4 and Table S2 (ESI†). The optimal GdF₃ content is 7 mol%. Therefore, in this work, the content of GdF₃ is fixed at 7 mol%.

Table 2 I _XEL (compared with BGO) and spatial resolution of Cu⁺-doped scintillators and other reported scintillators

Materials	Type	I XEL (%)	Spatial resolution (lp mm^−1)	Ref.
BGO	Crystal	100	—
Na2O–Gd2O3–BaO–B2O3–P2O5–Tb2O3	Glass	52	10	34
SiO2–B2O3–GdF3–CaO–Tb2O3–Dy2O3	Glass	38.2	—	35
BaCl2:Eu^2+	Glass ceramics	132	20	36
SiO2–KF–LaF3–GdF3–CeF3	Glass ceramics	170	—	37
B2O3-CaF2-Al2O3-Y2O3-Si3N4-Cu2O	Glass	37.8	—	38
SiO2–Al2O3–CaF2–NaF–CuO1/2–Al	Glass	141	20	19
Cs3Cu2I5Sb@PMMA	Perovskite	—	12	39
Cs3Cu2I5@PMMA	Perovskite	—	12.5	40
GCu3Al5.5	Glass	176	20	This work

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Refractive index (n), density (ρ) and effective atomic number (Z_eff) are fundamental parameters for glass scintillators. These parameters of GCuXAlY samples are measured (or estimated) and listed in Table S3 (ESI†).

Based on the XCOM web database, the X-ray absorption capacity of GCu3Al5.5 is compared with that of several commercial scintillators and Si. The result is given in Fig. 4(c). GCu3Al5.5 has X-ray attenuation capability close to BGO, higher than Si and comparable to Y₃Al₅O₁₂:Ce (YAG:Ce) in the range of 50–150 KeV. Commonly used X-ray photons have energy between 16 and 150 keV. This demonstrates that GCu3Al5.5 has an excellent X-ray attenuation capability. As displayed in Fig. 4(d), the X-ray attenuation efficiency of GCu3Al5.5 with thickness of 2 mm reaches 99.99% when the X-ray photon energy is 70 KeV. The GCu3Al5.5 for X-ray imaging is polished to 0.5 mm and its X-ray attenuation efficiency is 97%. Therefore, it can be used as an X-ray scintillation screen with thin thickness.

Irradiation stability is one of the crucial factors used to determine the performance of a scintillator in practical applications of X-ray imaging. Therefore, it is necessary to research the dynamic response of glass samples under prolonged irradiation. GCu3Al5.5 was continuously irradiated for 2 hours and the XEL spectra of GCu3Al5.5 were measured every 5 min. Fig. 4(e) reveals the time-dependent integrated XEL intensity of GCu3Al5.5. The XEL spectra during irradiation are shown in Fig. S5(a) (ESI†). The XEL intensity increases gradually in the first 40 min and reaches 1.5 times the XEL at 0 min, then stabilizes at this level within the next 80 min. This phenomenon is called the “bright burn effect” and can be explained as follows. There are traps in glass samples. They form a competitive relationship with the luminescent centers in the process of capturing charge carriers. In the first 40 min of irradiation, the charge carriers gradually fill the traps and more charge carriers are captured by Gd³⁺ and Cu⁺. So, the XEL intensity increases during this period. When the traps are filled completely, the carriers are only caught by the luminescent centers (Gd³⁺, Cu⁺), and the XEL intensity remains stable with increased irradiation time. After 120 min of irradiation, GCu3Al5.5 sample still maintains a high transmittance, as shown in Fig. S5(b) (ESI†), indicating that GCu3Al5.5 sample has excellent radiation resistance capacity.

Fig. 4(f) presents the linear relationship between XEL intensity and the radiation dose rate of GCu3Al5.5. For the purpose of excluding the influence of the “bright burn effect”, GCu3Al5.5 was irradiated for 40 min before test. The correlation coefficient (R²) of 99.86% proves that GCu3Al5.5 has excellent X-ray image contrast and it will contribute to high spatial resolution.^30,41,42

A homemade X-ray imaging system (shown in Fig. S6, ESI†) is used to achieve X-ray imaging. The GCu3Al5.5 with optimal scintillating performance is polished to 0.5 mm. Fig. 5(a)–(c) show the daylight photographs of chip, capsule containing nail, and resolution test standard line pair card. Fig. 5(d)–(g) show the X-ray images of chip, capsule containing spring, capsule containing nail, and resolution test standard line pair card obtained with GCu3Al5.5 as scintillator. When irradiated by X-ray, GCu3Al5.5 scintillator emits bright blue light. The spatial resolution of glass scintillator in Fig. 5(g) comes up to 20 lp mm⁻¹, higher than many reported scintillators listed in Table 2. This demonstrates that GCu3Al5.5 has promising applications for finer X-ray imaging.

Fig. 5 Photographs under sunlight and corresponding X-ray imaging of chip (a) and (d), X-ray image of capsule containing spring (e), capsule containing nail (b) and (f) and standard X-ray test line pair card (c) and (g).

Fig. 6 discloses the scintillation mechanism of XEL for GCu3Al5.5 glass. It is usually divided into three continuous processes: conversion, transport, and luminescence. Firstly, under X-ray irradiation, GCu3Al5.5 glass produces plenty of carriers (high-energy holes and electrons) due to Compton scattering and the photoelectric effect. A lot of secondary electrons are generated after carriers are thermalized. Secondly, traps capture some of the secondary electrons. Another part of secondary electrons is transported to luminescent centers (Gd³⁺ and Cu⁺). Finally, by absorbing energy of secondary electrons, Gd³⁺ and Cu⁺ are excited to excited states. For Gd³⁺, the electrons at excited states non-radiatively relax to the first excited energy level ⁶P_7/2, and then radiatively relax to ground state ⁸S_7/2 with emitting light.^33,37,43 Since the ⁶P_J (J = 3/2, 5/2, 7/2) states of Gd³⁺ and ³T_2g and other nearby energy levels of Cu⁺ have the same energy, a part of electrons in ⁶P_J levels of Gd³⁺ can easily transfer energy to nearby Cu⁺ ions non-radiatively. The electrons of Cu⁺ are excited to excited states. For Cu⁺, after non-radiative relaxation, the electrons relax from ¹T_2g, ³T_2g and ¹E_g states to ³E_g luminescent state, and then transition back to the ¹A_g level, producing blue luminescence.^44,45

Fig. 6 Scintillation mechanism under X-ray excitation (the CB and VB are the conduction band and valence band).

4. Conclusion

The PL and XEL properties of Cu⁺ doped glass scintillators have been significantly improved with three strategies of introducing a reducing agent, energy transfer and glass host selection. Due to the introduction of an appropriate amount of reducing agent Al, no Cu NPs are produced and the oxidation of Cu⁺ to Cu²⁺ is inhibited. By introducing the sensitizer Gd³⁺, the density and X-ray absorption capacity of glass samples are increased. Furthermore, the PL intensity and XEL intensity of Cu⁺ are improved by the energy transfer from Gd³⁺ to Cu⁺. Benefitting from high transparency of the fluoroaluminosilicate glass host, glass samples have high transmittance. In brief, the optimal sample GCu3Al5.5 with excellent luminescent and scintillating properties is obtained based on three strategies. The high transmittance (80.4%@547 nm), excellent X-ray absorption capacity, high IQE (76.2%@273 nm), high XEL intensity (176% of that of BGO), linear relationship between dose rate and XEL intensity (R² = 99.86%) and outstanding spatial resolution (20 lp mm⁻¹) suggest that Cu⁺ doped fluoroaluminosilicate glass might have broad application prospects in X-ray imaging.

Data availability

The authors confirm that the data supporting the findings of this study are available within the article and/or its ESI.† The data that support the findings of this study are available upon reasonable request from the corresponding author.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work was supported by NSFC (Grant No. 11974315), and the Natural Science Foundation of Zhejiang Province (Grant No. LZ20E020002).

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4tc04184d

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