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Article

Large-Diameter Bulk Crystal Growth and Scintillation Characterization of Thallium-Based Ternary Halide Crystals for Detection and Imaging

1
Xtallized Intelligence, Inc., Chapmansboro, TN 37035, USA
2
Department of Life and Physical Sciences, Physics Division, Fisk University, 1000 17th Avenue N, Nashville, TN 37208, USA
3
Harvard Medical School/Massachusetts General Hospital, Charlestown, MA 02129, USA
*
Author to whom correspondence should be addressed.
Crystals 2025, 15(6), 502; https://doi.org/10.3390/cryst15060502
Submission received: 24 April 2025 / Revised: 19 May 2025 / Accepted: 23 May 2025 / Published: 25 May 2025

Abstract

:
Scintillators are important for a wide range of applications in detection and imaging. In this paper, the growth and performance results of advanced large-diameter thallium-based ternary halide crystals are presented. Intrinsic crystals of TlMgCl3, TlCaCl3, and other small-diameter TlCaBr3, and TlCa(Cl,Br)3, as well as europium-doped TlCa2Br5, TlCa(Cl,Br)3, and TlSr2I5 are melt-grown by the Bridgman method. These compounds have a high effective atomic number (Zeff) and physical densities due to thallium. The best crystal quality and energy resolution (FWHM) at 662 keV are observed for TlMgCl3, TlCaCl3, and TlSr2I5:Eu at 3.8%, 4.6%, and 3.5%, respectively. The primary decay constants for these compounds are in the range of 0.45 to 0.63 μs. These ternary Tl-halide compounds have proportional or linear response (±0.05%) to γ-rays above 40 keV.

1. Introduction

Advancement in high-energy physics depends largely on the advancement in materials research. The need for new low-cost, bright, high-performing bulk scintillators for high-energy particle detectors requires more research in scintillation materials with properties suitable for the application [1]. Some of the most studied radiation detector materials currently available in the market are inorganic binary compound scintillators [2]. Ternary compounds that are based on these binary compounds are usually formed by adding metal cations. Initial examples of these ternary compounds are listed in an online table [2], and many more ternary compounds have been published in recent years. These recent advances in materials study for radiation sensors, particularly the latest discovery of high-density thallium-based inorganic scintillation crystals, are spurred by a necessity to improve isotope identification capability, for example, for homeland security applications. These new materials also possess many of the required properties for detection materials in high-energy physics applications and research, as well as other fields such as medical imaging and oil well logging. The continuous search for improved scintillation materials for better radiation detection is important, since an ideal scintillator for such applications has yet to be discovered.
Recently, high-detection-efficiency Tl-based scintillation crystals have attracted a good amount of attention from worldwide scintillator researchers. These compounds, for example Ce-doped Tl2LaCl5 (TLC) [3,4,5,6], as well as intrinsic (i.e., not doped) TlMgCl3 (TMC) and TlCaI3 (TCI) [7,8], have been investigated and very promising initial results have been published. These new compounds are of high densities (>5 g/cm3), are bright (light yields between 31,000 and 76,000 ph/MeV for 662 keV photons), have fast decay times (36 ns (89%) for TLC; 46 ns (9%) for TMC; 62 ns (13%) for TCI), and have moderate melting points (between 500 and 700 °C). Other compounds that have been investigated in the past ten years include Tl2HfCl6 [9,10,11], Tl2ZrCl6 [9,11,12], Tl2LaBr5:Ce [5,13], and Tl2CeCl5 [14]. As seen in these published results, Tl-based scintillators, such as the ones previously mentioned, have promising properties desirable for high-energy physics as well as homeland security applications [3,4,5,6,7,8,9,10,11,12,13,14,15,16].
Following the results of studied compounds, Xtallized Intelligence, Inc. (XI, Inc.) has grown several large-diameter (≥14 mm) single bulk crystals of intrinsic and doped thallium-based ternary compound scintillators for high energy physics and other applications. Table 1 shows a list of compounds grown and characterized by XI, Inc. For high-energy physics purposes, physical dimensions of a detection material should accommodate at least 20 times the radiation length of the material. Therefore, to obtain amenable crystals, the large-diameter growth of crack-free, single crystals of high quality and performance must be accomplished. In the following sections, the growth and crystal analysis of intrinsic crystals of TlMgCl3, TlCaCl3, TlCaBr3, and TlCa(Cl,Br)3, as well as europium-doped TlCa2Br5, TlCa(Cl,Br)3, and TlSr2I5 are presented.

2. Materials and Methods

Each of the Tl-based ternary compounds was grown by stoichiometric mixing of the respective binary compounds and growing them by the vertical Bridgman technique [17]. Table 1 shows the ternary compounds that have been grown by XI, Inc. (Chapmansboro, TN, USA). Starting materials of the highest available purity (up to 99.995%) were purchased from US-based chemical vendors APL Engineered Materials, Millipore Sigma, and Thermo Fisher Scientific. For each targeted ternary compound, stoichiometric amounts of the binary compounds and dopants were purified, if necessary, and loaded into a freshly cleaned and baked quartz ampoule sized 16 mm and 1 inch in inner diameter. Material loading was conducted inside an inert glove box with an argon atmosphere. Using a turbo vacuum pump, the loaded ampoule was dehydrated, if necessary, and then sealed in a high vacuum. The ampoule was placed in a two-zone vertical furnace for growth. The top zone of the furnace was set a few degrees above the melting temperature of the compound to ensure a complete melt. The bottom zone was set a few degrees below the crystallization temperature for the compound. The growth was conducted at a rate of 25–35 mm/day. After the crystallization was completed, the ampoule was cooled down 75–150 °C/day to room temperature. The crystal was then retrieved from the growth ampoule and samples were extracted, lapped, and polished for analysis.
For sample characterization, each polished sample was hermetically encapsulated or packaged. The packaged crystal was then coupled to a Hamamatsu R6231-100 photomultiplier tube (PMT) with BC-630 silicone optical coupling compound. The PMT was biased with a Hamamatsu C9525 High Voltage Power Supply and the PMT anode signals were processed through a chain of equipment (a Canberra 2005 preamplifier, a Canberra 2022 spectroscopy amplifier, and an Amptek MCA8000D multichannel analyzer (MCA)) for gamma-ray spectroscopy.
After background subtraction, the 662 keV full energy peak from 137Cs was analyzed to determine the energy resolution of each scintillator and relative light yield with respect to NaI:Tl. Similarly, after background subtraction, full energy peak and x-ray peak positions and full-width half maxima (FWHMs) from other gamma ray sources, such as 241Am (60 keV), 133Ba (31 keV, 53 keV, 81 keV, 276 keV, 303 keV, 356 keV, and 384 keV), 22Na (511 keV and 1275 keV), 60Co (1173 keV and 1333 keV), and 152Eu (40 keV, 122 keV, 245 keV, 344 keV, 779 keV, 964 keV, 1112 keV, and 1408 keV) were also used to determine relative light yield (i.e., non-proportionality) and energy resolution data, respectively. Energy uncertainties were obtained from the 1999 edition of Table of Isotopes [18] and were treated as one standard deviation [19]. Peak position uncertainties were calculated from their respective FWHMs. Error bars on non-proportionality data were calculated by using the division error propagation formula on energy and peak position uncertainties.
Decay time was determined by recording the PMT anode signals using a CAEN DT5720 digitizer. The signals were analyzed offline by first normalizing each signal pulse then adding the normalized pulses to get an average decay curve or temporal data. The averaged data were fitted with an exponential decay function expressed in Equation (1) as follows:
y = y 0 + i = 1 N A i e x x 0 t i ,
where x0 and y0 are the x-axis and y-axis offsets, ti is the ith time constant, and A i = f i t i , where fi is the fraction of ti. The ExpDecayn (n = 1, 2, or 3) fitting procedure in Origin® 2019 software was used for this analysis. The associated standard errors (i.e., standard deviations [20]) on the decay constants from this analysis were noted as uncertainties.
X-ray excited optical luminescence spectra were collected from polished samples of TlMgCl3, TlCaBr3, and TlCa2Br5:Eu. The spectrum collection was carried out using an x-ray tube source that provided <30 keV x-rays and the emission was collected by a fiberoptic-coupled Ocean Optics spectrometer, employing a silicon CCD readout.

3. Results

To start this material investigation and in order to keep both research cost and material waste low, small-diameter (14-to-16 mm) crystal growth runs were carried out initially. After measurements of optical and physical properties, the most promising compounds that were also feasible for larger-diameter crystal growth were grown in 1-inch-diameter sizes.

3.1. 16 mm Diameter Crystal Growth

3.1.1. Intrinsic TlMgCl3

The investigation into the growth of TlMgCl3 was started by growing ∅16 mm crystal boules, then followed by scaling up to several ∅1″ boules. From the ∅16 mm boule, similarly sized (12 × 15 × 15 mm3) single, transparent, crack-free crystal samples of TlMgCl3 were successfully obtained from three different areas in the crystal boule, which were the tip (first to freeze), mid (dle), and tail (last to freeze), respectively, to check the crystal homogeneity and to measure the performance along the growth direction.
Figure 1a shows 137Cs spectra collected by thinner samples retrieved along the growth direction of the 16 mm diameter TlMgCl3 boule that show a similar detector performance (similar energy resolution ~ 4.6% at FWHM for 662 keV, as well as similar full-energy peak position or relative light yield), indicating that the boule was uniform. Because TlMgCl3 had no dopant (i.e., intrinsic) and the growth involved a stoichiometric composition, the crystal performance along the boule was expected to be uniform. Uniformity in a detector volume is important especially when an application requires that the entire detector volume be involved in detection. Tl characteristic x-ray escape peaks (low energy peaks adjacent to the full energy peaks) were commonly observed in these spectra collected with thin samples of compounds with a high Z constituent. Figure 1b shows 137Cs spectra collected at different amplifier shaping times, with the best energy resolution of 4.4% (FWHM) at 662 keV obtained with a 4 μs shaping time.
The comparison of a 137Cs spectrum collected with the TlMgCl3 sample and that collected with a ∅1″× 1″ (∅ 2.54 cm × 2.54 cm) NaI:Tl produced by Saint Gobain is shown in Figure 1c, showing that TlMgCl3 has an excellent peak-to-Compton ratio (PCR) of 7.05 even for a small-sized crystal, compared to a PCR of 5.44 for the ∅1″× 1″ NaI:Tl crystal. Figure 1d shows the x-ray emitted optical luminescence spectrum of TlMgCl3 that shows a broad emission band with a maximum around 436 nm, which is higher than a previously published maximum of 409 nm [7]. Considering the spectral response or quantum efficiency of a PMT with a super bialkali photocathode [21], the emission spectra of both TlMgCl3 (Figure 1d) and NaI:Tl [22], as well as the published light yield of 38,000 photons/MeV for NaI:Tl [19], the estimated light yield for TlMgCl3 is 28,000 photons/MeV, which is slightly lower than a previously published number of 30,600 photons/MeV [7]. It is worth noting that there is a difference in the x-ray emission spectrum in Figure 1d and previously published spectrum in [7], which has a maximum of 409 nm. It is also worth noting that the previously published result was based on the analysis of a much thinner and smaller crystal.
Figure 1e shows one of the polished TlMgCl3 crystal samples from the 16 mm diameter TlMgCl3 crystal boule. Figure 1f shows the non-proportionality data indicating that the response of TlMgCl3 to γ-rays is linear (±0.05%) for energy above 30 keV. Decay time was measured and analyzed using Equation (1) with N = 3, resulting in decay constants of 74 ns ± 1 ns (4%), 338 ns ± 4 ns (50%), and 572 ns ± 7 ns (46%) (Figure 1g).

3.1.2. Intrinsic TlCaCl3

As in the case with TlMgCl3, the investigation into the growth for TlCaCl3 was started by growing ∅16 mm crystal boules, and then it was scaled up to several ∅1″ boules. From the 16 mm diameter boule, similarly sized (approximately 3 × 7 × 10 mm3) single, transparent, crack-free crystal platelet-like samples of TlCaCl3 were successfully obtained from three different areas in the crystal boule (top, middle, and tail, respectively) to check for crystal homogeneity and to measure the performance along the growth direction. Figure 2a shows 137Cs spectra collected by the polished TlCaCl3 samples (inset pictures) that were retrieved along the direction of the growth. The pictures of the crystals were taken after all measurements were completed in a non-inert atmosphere environment; thus, due to the hygroscopicity of the crystals, the samples slightly degraded and turned hazy. The 137Cs spectra shows similar energy resolution (approximately 4.6% FWHM at 662 keV) and similar full-energy peak positions, which indicates that the boule was uniform in quality and performance. As in the case with TlMgCl3, because TlCaCl3 was also an intrinsic scintillator and the growth involved a stoichiometric composition, the crystal performance along the boule was also expected to be uniform. 137Cs spectra collected with a slightly large sized TlCaCl3 crystal (9 × 10 × 10 mm3) at different amplifier shaping times resulted in a best energy resolution of 5.2% (FWHM) at 2 μs shaping time (Figure 2b).
137Cs spectra comparison between the TlCaCl3 sample and a ∅1″× 1″ (∅ 2.54 cm × 2.54 cm) NaI:Tl is shown in Figure 2c. Using the published emission spectrum of TlCaCl3 [8], the estimated light yield for TlCaCl3 is 22,000 photons/MeV. The analysis on the temporal profile in Figure 2d, using Equation (1) and N = 3, shows that the decay constants for TlCaCl3 are 81 ns ± 2 ns (2%), 409 ± 4 ns (62%), and 966 ns ± 17 ns (36%). Non- proportionality data in Figure 2e show that the response of TlCaCl3 to γ-rays is linear (±0.05%) for energy above 30 keV.

3.1.3. Intrinsic TlCaBr3

137Cs spectra collected at different amplifier shaping times for a TlCaBr3 sample are shown in Figure 3a, with a best measured energy resolution of 5.3% (FHWM) at 662 keV collected at a 12 μs shaping time. The comparison of 137Cs spectra collected with a TlCaBr3 sample from the ∅14 × 20 mm boule and a ∅1″ × 1″ NaI:Tl is shown in Figure 3b, showing that even with a smaller diameter, TlCaBr3 exhibited a larger peak-to-Compton ratio than NaI:Tl. The x-ray excited optical luminescence spectrum of TlCaBr3 is shown in Figure 3c, showing a broad band with a maximum around 517 nm. Using this emission data, the light yield for TlCaBr3 is estimated to be 54,000 photons/MeV. 152Eu spectrum was also collected with TlCaBr3 (Figure 3d), from which the relative light yield data were calculated to determine the non-proportionality behavior of TlCaBr3 (Figure 3e). As in the case of other ternary Tl-based halide crystals described so far, the crystal had a linear response (±0.05%) to γ-rays with energy above 30 keV. The analysis on the temporal profile in Figure 3f, using Equation (1) and N = 3, shows that the decay constants for TlCaBr3 are 328 ns ± 1 ns (11%), 788 ns ± 13 ns (44%), and 3.28 μs ± 0.06 μs (45%).

3.1.4. Intrinsic and Eu-Doped TlCa2Br5

Intrinsic and Eu-doped ∅16 mm crystal boules of TlCa2Br5 were grown, processed, and characterized. The undoped crystal did not appear clear or transparent, indicating that there was probably more than one phase in the crystal boule. A dopant (Eu2+, with 3% concentration) was utilized in attempt to improve scintillation properties, like light yield, energy resolution, and decay time. Figure 4a shows 137Cs spectrum collected with the Eu-doped TlCa2Br5 crystal, where an energy resolution of 4.2% (FWHM at 662 keV) was measured. Figure 4b shows the comparison between 137Cs spectra collected with TlCa2Br5:Eu and NaI:Tl. Figure 4c shows the x-ray excited optical luminescence spectrum of TlCa2Br5:Eu, with a maximum peak around 484 nm. With this data, the light yield of TlCa2Br5:Eu is estimated to be 42,000 photons/MeV. According to the relative light yield vs. photon energy (non-proportionality) data (Figure 4d), TlCa2Br5:Eu has a relatively linear response (±0.05%) for a wide range of photon energy, especially for energies above 40 keV. Doping with europium appears to improve energy resolution; however, crystal quality appears to have been compromised. Temporal data were measured, and with N = 2 in Equation (1), two decay constants were calculated (Figure 4e): 552 ns ± 7 ns (46%) and 1.63 μs ± 0.04 μs (54%).

3.1.5. Intrinsic and Eu-Doped Mixed Halide TlCa(Cl,Br)3

In an effort to improve the scintillation properties of bromine-based TlCaX3 compounds, several approaches were considered in this research. As seen previously, undoped TlCaBr3 was first grown as the base for comparison. Next, Eu-doped TlCa2Br5 was grown, which resulted in a better energy resolution, while the crystal quality and light yield suffer. In this section, results from intrinsic and Eu-doped mixed halide TlCa(Cl,Br)3, with 50:50 Cl/Br mol ratio, are presented.
Figure 5a shows 137Cs spectra collected with an intrinsic TlCa(Cl,Br)3 sample at different amplifier shaping times, with a best energy resolution of 5.2% (FWHM) collected at a 12 μs shaping time. Figure 5b shows the temporal profile for intrinsic TlCa(Cl,Br)3, with decay constants of 378 ns ± 12 ns (18%), 621 ns ± 11 ns (61%), and 2.61 μs (21%). The decay constants are similar in orders of magnitude and fraction sizes to those of TlCa2Br5:Eu. The comparison of 137Cs spectra collected by TlCa(Cl,Br)3 and NaI:Tl is shown in Figure 5c. Using the emission spectrum of TlCaBr3 (Figure 3c), the light yield of TlCa(Cl,Br)3 is estimated to be 71,000 photons/MeV.
Following the study presented in the previous sections, europium doped TlCa(Cl,Br)3 (with 3% Eu2+ concentration) were grown, with the results shown in Figure 5d,e. The crystals extracted from along the boule were not transparent; however, the crystals had similar performances (energy resolution of 5.5–5.8% (FWHM) at 662 keV, as well as primary decay constant of 0.50–0.58 μs, as the decay constants of TlCa(Cl,Br)3:Eu were measured at 505 ns ± 3 ns (62%), 1.08 μs ± 0.06 μs (22%), and 4.25 μs ± 0.29 μs (16%) (Figure 5d)), indicating that the boule was grown uniformly. Adding dopant to the mixed halide TlCaX3 did not result in an observable improvement in the energy resolution nor in the decay constants. Using the emission spectrum of TlCaBr3 (Figure 3c), the light yield of TlCa(Cl,Br)3:Eu is estimated to be 63,000 photons/MeV, which is slightly less than the undoped sample (Figure 5c).

3.2. 1-Inch-Diameter Crystal Growth

From the scintillation results of the 16 mm diameter crystal growth, as well as the crystal growth yield results, it was evident that some of the compounds were feasible for a scale-up effort, namely intrinsic TlMgCl3 and TlCaCl3 scintillators, due to their reproduceable crystal yield, quality, and performance, as well as the non-existence phase issue. Also feasible for scale up was europium-doped TlSr2I5, whose small diameter growth and initial 1-inch-diameter growth were previously reported [8,9,10]. The following sections describe the latest 1-inch-diameter growth results of the aforementioned compounds.

3.2.1. Intrinsic TlMgCl3

Better purification processes and finely tuned temperature profiles improved the growth of several boules of 1-inch-diameter TlMgCl3 (Figure 6a). Visible on these boules were dark inclusions, which were residual impurities that were pushed out of the boules and reacted with the walls of the quartz ampoules. From these boules, several ∅1″ × 1″ TlMgCl3 were cut and processed. Figure 6b shows three as polished ∅1″ × 1″ TlMgCl3 crystals (top pictures) that were then permanently encapsulated (bottom picture). Although TlMgCl3 is non hygroscopic, the encapsulation provides protection from accidental mechanical damage.
Figure 7a shows 137Cs spectra by one of the ∅1″ × 1″ TlMgCl3 crystals with different amplifier shaping times, resulting in a best energy resolution of 3.8% (FWHM) at 662 keV for 8 μs. This measurement was slightly better than the results obtained by the smaller crystals (Figure 1), which could be attributed to better processing or shaping of the crystal (right cylinder vs. cuboid) that promotes better light collection, better post-growth crystal processing (i.e., better polishing without cracking or cleaving), and/or better crystal quality (lack of defects or imperfections). Further study on light collection in TlMgCl3 may be needed. Figure 7b shows the temporal data for the 1-inch TlMgCl3, with measured decay constants of 71 ns ± 1 ns (4%), 321 ns ± 3 ns (47%), and 548 ns ± 4 ns (49%), which are comparable to the decay constants obtained for the smaller crystals (Figure 1g).

3.2.2. Intrinsic TlCaCl3

An as-grown bulk ∅1″ TlCaCl3 single crack-free crystal boule is shown in Figure 8a. The outside of the boule was covered with a thin translucent layer that may have been organics or impurities due to an excess of chloride reacting with the quartz ampoule. Under this translucent layer was a single crack-free crystal, a sample of which was shown in Figure 8b before packaging, a rectangular cuboid with the size of 16 × 16 × 25 mm3, which was subsequently polished and hermetically encapsulated (Figure 8c). The encapsulated crystal was characterized by collecting 137Cs and 152Eu spectra, as well as collecting the PMT anode signals to determine the temporal profile and determine decay time constants. Figure 8d shows the 137Cs spectrum collected by the encapsulated TlCaCl3 sample with a measured 4.6% (FWHM) energy resolution at 662 keV. Using the 137Cs spectra comparison between TlCaCl3 and NaI:Tl crystals (Figure 8d), the light yield of the 1-inch sample of TlCaCl3 is estimated to be 19,000 photons/MeV. As also observed in Figure 8d, for a slightly sized crystal (16 × 16 × 25 mm3) than NaI:Tl (∅1″ × 1″), TlCaCl3 has a much better peak-to-Compton ratio (PCR) than NaI:Tl. Decay constants of 104 ns ± 1 ns (3%), 456 ns ± 2 ns (72%), and 1.28 μs ± 0.02 μs (25%) were measured (Figure 8e). These decay constants were slightly longer than the results of the smaller crystals (Figure 2d); however, they were still in the same order of magnitude. 152Eu spectrum was also collected (Figure 8f), from which the relative light yield data were calculated to determine the non-proportionality behavior of TlCaCl3 (Figure 8g). As in the case of the smaller sized TlCaCl3 crystals, the crystal had a linear response (±0.05%) to γ-rays with energy above 100 keV.

3.2.3. Eu-Doped TlSr2I5

Eu-doped TlSr2I5 crystal growth started with ∅16 mm [13], and then scaled up to several ∅1″ crystal boules. The latest 1-inch-diameter TlSr2I5:Eu as-grown crystals are shown in Figure 9a. The 137Cs spectrum collected with a ∅1″ × 1″ TlSr2I5:Eu sample is shown in Figure 9b, with an energy resolution of 3.5% (FWHM) at 662 keV. Tl escape peak was detected around ch. no. 1470; however, due to the large crystal size, it was not as prominently featured in the spectrum as in the case of a thin TlSr2I5:Eu sample.

4. Discussion

The results and properties of ternary Tl-halide crystal successfully grown and investigated for imaging and high-energy particle physics applications are shown in Table 2. These compounds have high Zeff due to thallium and they are expected to have high physical densities. The peak-to-Compton ratio (PCR) for small-sized crystals, especially TlMgCl3 and TlCaCl3, at 662 keV are comparable or better than a ∅1″ × 1″ NaI:Tl, due to better energy resolution and full-energy peak efficiency. Overall, the improvement in crystal growth and performance in 1-inch-diameter vs. 16 mm diameter crystals is due to the effect of material purification in the lab. The best crystal quality and energy resolution (FWHM) at 662 keV were observed for intrinsic TlMgCl3. Additionally, TlMgCl3 is not hygroscopic. The primary decay constants for these compounds are in the range of 0.45 to 0.63 μs. All of these compounds have proportional or linear response (±0.05%) to γ-ray above 100 keV. Intrinsic TlMgCl3 and TlCaCl3, as well as TlSr2I5:Eu, are feasible for large-diameter growth (≥1-inch-diameter) due to uniformity in crystal quality and detector performance along the boule. Currently, a scale-up effort of up to 2-inch-diameter crystal growth is in the process and will be reported in the near future.

Author Contributions

Conceptualization: R.H.; data curation: R.H. and E.A.; formal analysis: R.H., E.A. and H.S.; funding acquisition: R.H.; investigation: R.H. and H.S.; methodology: R.H., E.A. and H.S.; project administration: R.H.; resources: R.H. and H.S.; supervision: R.H. and H.S.; validation: R.H.; visualization: R.H. and E.A.; writing—original draft: R.H. and E.A.; and writing—review and editing: R.H. and E.A. All authors have read and agreed to the published version of the manuscript.

Funding

This research was partially funded by the U.S. Department of Energy, grant number DE-SC0022792.

Data Availability Statement

The datasets presented in this article are not readily available. Requests to access the datasets should be directed to the corresponding author.

Conflicts of Interest

Author Rastgo Hawrami was employed by the company Xtallized Intelligence, Inc. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of.

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Figure 1. (a) 137Cs spectra collected by similarly sized (12 × 15 × 15 mm3) samples extracted from the first TlMgCl3 boule along the growth direction. (b) 137Cs spectra collected by a TlMgCl3 sample at different amplifier shaping times. (c) Comparison of 137Cs spectra collected with TlMgCl3 and NaI:Tl. (d) X-ray excited optical luminescence spectrum of TlMgCl3. (e) A polished TlMgCl3 sample. (f) Non-proportionality data for TlMgCl3. (g) Decay time measurements for TlMgCl3.
Figure 1. (a) 137Cs spectra collected by similarly sized (12 × 15 × 15 mm3) samples extracted from the first TlMgCl3 boule along the growth direction. (b) 137Cs spectra collected by a TlMgCl3 sample at different amplifier shaping times. (c) Comparison of 137Cs spectra collected with TlMgCl3 and NaI:Tl. (d) X-ray excited optical luminescence spectrum of TlMgCl3. (e) A polished TlMgCl3 sample. (f) Non-proportionality data for TlMgCl3. (g) Decay time measurements for TlMgCl3.
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Figure 2. (a) 137Cs spectra collected by samples (approximately 3 × 7 × 10 mm3) extracted from a 16 mm diameter TlCaCl3 boule along the growth direction. (b) 137Cs spectra collected by a 9 × 10 × 10 mm3 TlCaCl3 sample at different amplifier shaping times. (c) Comparison of 137Cs spectra collected with TlCaCl3 and NaI:Tl. (d) Decay time measurements for the TlCaCl3. (e) Non-proportionality data for TlCaCl3.
Figure 2. (a) 137Cs spectra collected by samples (approximately 3 × 7 × 10 mm3) extracted from a 16 mm diameter TlCaCl3 boule along the growth direction. (b) 137Cs spectra collected by a 9 × 10 × 10 mm3 TlCaCl3 sample at different amplifier shaping times. (c) Comparison of 137Cs spectra collected with TlCaCl3 and NaI:Tl. (d) Decay time measurements for the TlCaCl3. (e) Non-proportionality data for TlCaCl3.
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Figure 3. (a) 137Cs spectrum collected with a TlCaBr3 at different shaping times. (b) Comparison of 137Cs spectra collected with a TlCaBr3 sample from the ∅14 × 20 mm boule and a ∅1″ × 1″ NaI:Tl. (c) X-ray excited optical luminescence spectrum of TlCaBr3. (d) 152Eu spectrum collected with TlCaBr3. (e) Non-proportionality data for TlCaBr3. (f) Decay time measurements for TlCaBr3.
Figure 3. (a) 137Cs spectrum collected with a TlCaBr3 at different shaping times. (b) Comparison of 137Cs spectra collected with a TlCaBr3 sample from the ∅14 × 20 mm boule and a ∅1″ × 1″ NaI:Tl. (c) X-ray excited optical luminescence spectrum of TlCaBr3. (d) 152Eu spectrum collected with TlCaBr3. (e) Non-proportionality data for TlCaBr3. (f) Decay time measurements for TlCaBr3.
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Figure 4. (a) 137Cs spectrum collected with a TlCa2Br5:Eu crystal sample. (b) Comparison of 137Cs spectra collected with TlCa2Br5:Eu and NaI:Tl. (c) X-ray excited optical luminescence spectrum of TlCa2Br5:Eu. (d) Non-proportionality data for TlCa2Br5:Eu. (e) Decay time measurements for TlCa2Br5:Eu.
Figure 4. (a) 137Cs spectrum collected with a TlCa2Br5:Eu crystal sample. (b) Comparison of 137Cs spectra collected with TlCa2Br5:Eu and NaI:Tl. (c) X-ray excited optical luminescence spectrum of TlCa2Br5:Eu. (d) Non-proportionality data for TlCa2Br5:Eu. (e) Decay time measurements for TlCa2Br5:Eu.
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Figure 5. (a) 137Cs spectra collected with a TlCa(Cl,Br)3 sample at different amplifier shaping times. (b) Decay time measurements for TlCa(Cl,Br)3. (c) Comparison of 137Cs spectra collected with TlCa(Cl,Br)3 and NaI:Tl. (d) Decay time measurements for Eu-doped TlCa(Cl,Br)3. (e) 137Cs spectrum collected with a TlCa(Cl,Br)3:Eu sample.
Figure 5. (a) 137Cs spectra collected with a TlCa(Cl,Br)3 sample at different amplifier shaping times. (b) Decay time measurements for TlCa(Cl,Br)3. (c) Comparison of 137Cs spectra collected with TlCa(Cl,Br)3 and NaI:Tl. (d) Decay time measurements for Eu-doped TlCa(Cl,Br)3. (e) 137Cs spectrum collected with a TlCa(Cl,Br)3:Eu sample.
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Figure 6. (a) Two as-grown 1-inch-diameter TlMgCl3, showing single, transparent, crack-free crystal boules. (b) Three as polished ∅1″ × 1″ TlMgCl3 crystals (top) that were permanently encapsulated (bottom).
Figure 6. (a) Two as-grown 1-inch-diameter TlMgCl3, showing single, transparent, crack-free crystal boules. (b) Three as polished ∅1″ × 1″ TlMgCl3 crystals (top) that were permanently encapsulated (bottom).
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Figure 7. (a) 137Cs spectra collected by a TlMgCl3 sample, extracted from the second boule, with different amplifier shaping times. (b) Decay time data for the TlMgCl3 sample.
Figure 7. (a) 137Cs spectra collected by a TlMgCl3 sample, extracted from the second boule, with different amplifier shaping times. (b) Decay time data for the TlMgCl3 sample.
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Figure 8. (a) As-grown ∅1″ TlCaCl3 crystal boule. (b) Roughly polished rectangular cuboid that was shaped from one of the TlCaCl3 samples. (c) Hermetically encapsulated TlCaCl3 crystal. (d) 137Cs spectrum collected by the sample in (c). (e) Decay time measured for TlCaCl3. (f) 152Eu spectrum collected by the sample in (c). (g) Non proportionality data for TlCaCl3.
Figure 8. (a) As-grown ∅1″ TlCaCl3 crystal boule. (b) Roughly polished rectangular cuboid that was shaped from one of the TlCaCl3 samples. (c) Hermetically encapsulated TlCaCl3 crystal. (d) 137Cs spectrum collected by the sample in (c). (e) Decay time measured for TlCaCl3. (f) 152Eu spectrum collected by the sample in (c). (g) Non proportionality data for TlCaCl3.
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Figure 9. (a) As-grown ∅1″ Eu doped TlSr2I5 crystal boule. (b) 137Cs spectrum collected with a TlSr2I5:Eu crystal.
Figure 9. (a) As-grown ∅1″ Eu doped TlSr2I5 crystal boule. (b) 137Cs spectrum collected with a TlSr2I5:Eu crystal.
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Table 1. List of ternary Tl-halide compounds grown and characterized.
Table 1. List of ternary Tl-halide compounds grown and characterized.
Compound
TlMgCl3∅16 mm∅1-inch
TlCaCl3∅16 mm∅1-inch
TlCaBr3∅14 mm
TlCa2Br5∅16 mm
TlCa2Br5:Eu∅16 mm
TlCa(Cl,Br)3∅16 mm
TlCa(Cl,Br)3:Eu∅16 mm
TlSr2I5:Eu∅16 mm∅1-inch
Table 2. Summary of results and properties of analyzed ternary Tl-halide crystals.
Table 2. Summary of results and properties of analyzed ternary Tl-halide crystals.
∅ 16 mm Crystals
CompoundZeffERTprimary
(ns)
Light Yield
(Photons/MeV)
TlMgCl369.74.6%338, 57228,000
TlCaCl368.95.2%40922,000
TlCaBr364.35.3%788, 3.28 μs54,000
TlCa2Br5:Eu66.24.2%1.63 μs42,000
TlCa(Cl,Br)364.35.2%62171,000
TlCa(Cl,Br)3:Eu66.35.5%50563,000
∅ 1-Inch Crystals
CompoundZeffERTprimary
(ns)
Light Yield
(Photons/MeV)
TlMgCl369.73.8%321, 54828,000
TlCaCl368.94.6%45919,000
TlSr2I5:Eu68.93.5%39572,000
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Hawrami, R.; Ariesanti, E.; Sabet, H. Large-Diameter Bulk Crystal Growth and Scintillation Characterization of Thallium-Based Ternary Halide Crystals for Detection and Imaging. Crystals 2025, 15, 502. https://doi.org/10.3390/cryst15060502

AMA Style

Hawrami R, Ariesanti E, Sabet H. Large-Diameter Bulk Crystal Growth and Scintillation Characterization of Thallium-Based Ternary Halide Crystals for Detection and Imaging. Crystals. 2025; 15(6):502. https://doi.org/10.3390/cryst15060502

Chicago/Turabian Style

Hawrami, Rastgo, Elsa Ariesanti, and Hamid Sabet. 2025. "Large-Diameter Bulk Crystal Growth and Scintillation Characterization of Thallium-Based Ternary Halide Crystals for Detection and Imaging" Crystals 15, no. 6: 502. https://doi.org/10.3390/cryst15060502

APA Style

Hawrami, R., Ariesanti, E., & Sabet, H. (2025). Large-Diameter Bulk Crystal Growth and Scintillation Characterization of Thallium-Based Ternary Halide Crystals for Detection and Imaging. Crystals, 15(6), 502. https://doi.org/10.3390/cryst15060502

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