Luminescence and scintillation properties of advanced Lu3Al5O12:Pr3+ single crystal scintillators

In this paper we present the luminescence and scintillation properties of Lu₃Al₅O₁₂:Pr (LuAG:Pr) single crystals with Pr³⁺ concentration of 0.13 wt %, grown by the Czochralski method. The light yield and energy resolution were measured under 662 keV γ-ray excitation. The dominant emission band peaking at 310 nm with a shoulder at 370 nm was observed in the photoluminescence spectrum. High light yield of 24,500 ph/MeV and an energy resolution of 5.3 % were obtained for a 6 × 6 × 2 mm³ LuAG:Pr sample. Light yield dependence on sample height and shaping time was measured. The estimated photofraction in pulse height spectrum and total mass attenuation coefficient at 662 keV γ-rays were also determined and compared with the theoretical ones calculated using the WinXCom program.     

Scintillation response of Y3Al5O12:Pr3+ single crystal scintillators

In this paper we present the photoluminescence (PL) and scintillation response of Pr³⁺-doped Y₃Al₅O₁₂ (YAG:Pr) single crystals grown by the Czochralski method with different Pr³⁺ concentrations of 0.16, 0.33, and 0.65 mol%. PL spectra and decay curves were measured for both the fast 5d → 4f and slow 4f → 4f emissions. The PL decay times were evaluated which evidence concentration quenching especially in ¹D₂ → ³H₄ emission for the highest Pr³⁺ concentration. Light yield (LY) of 15,600 photons per MeV and energy resolution of 6.4% at 662 keV γ-rays were obtained with the YAG:Pr (0.33%) crystal. The LY non-proportionality and energy resolution versus γ-ray energy were measured and the intrinsic resolution was calculated. A good proportionality of the LY was found within 7% over the energy range from 1274.5 keV down to 32 keV. The estimated photofraction in the pulse height spectra of 320 and 662 keV γ-rays was also determined and compared with the theoretical one calculated using WinXCom program.     

Near-infrared luminescence of OH and Cl doped Bi4Ge3O12 crystals

OH⁻ and Cl⁻ doped Bi₄Ge₃O₁₂ (BGO) single crystals had been grown by Vertical Bridgman (VB) method. The structure of these crystals was determined by XRD, the transmittance and emission spectra in near infrared region (NIR) were measured at room temperature. 5% OH⁻ doped BGO shows a significant emission band peaking around 1181 nm under 808 nm laser diodes (LDs) excitation, and the 5% Cl⁻ doped BGO exhibits a relatively weak emission band as well. 100% and 5% OH⁻ doped BGO show noticeable emission band centered at about 1346 nm under 980 nm LDs excitation.     

Luminescence and Scintillation Characterization of Cs2NaGdBr6: Ce3+ Single Crystal

Luminescence and scintillation properties of newly discovered bromo-elpasolites Cs₂NaGdBr₆: Ce³⁺ (CNGB: Ce³⁺) are presented. Single crystals of CNGB: Ce³⁺ with dimensions up to Ø7×10 mm³ are successfully grown by the Bridgman technique. X-ray excited luminescence measurements of the grown samples showed a broad emission band in the wavelength range from 365 to 470 nm. It offered an energy resolution of 5.1% (FWHM) at 662 keV for 10% Ce sample. The light output of the investigated samples increases along with cerium concentration. A maximum light yield of ～36,800 ph/MeV is measured for the 10% Ce sample crystal. Under γ-ray excitation, CNGB: Ce³⁺ crystals showed three exponential decay time components. The scintillation mechanism in the sample crystal is presented.     

Optical emissions of products sputtered from Fe, Fe2O3 and Fe3O4 powders

Powder iron has been bombarded by a 5 keV Kr⁺ ions in a vacuum better than 10^-7 torr and under few 10^-6 torr ultra pure oxygen partial pressure. The optical spectra of the sputtered particles were recorded between 340.0 nm and 410.0 nm. These spectra exhibit discrete lines, which are attributed to neutral excited atoms of iron. Two iron oxides, namely hematite (Fe₂O₃)_{3}) and magnetite (Fe₃O₄)_{4}), in powder form, were studied under the same experimental conditions and identical lines were observed in the obtained spectra. The absolute intensities of the spectral lines in all spectra were measured and the differences in the recorded yield photons were discussed in term of electron-transfer processes between the excited sputtered atom and the bombarded surface. In accordance with the proposed interpretation, we suggest values for the energy gaps and electronic affinities for the studied oxides and for the oxide layer that might be formed by the adsorption of oxygen atoms.     

Scintillation properties of Cs2LiGdCl6: Ce3+

In this communication, we investigated the scintillation properties of Cs₂LiGdCl₆:10% Ce³⁺ single crystal. This scintillation crystal is grown by using the vertical Bridgman technique. X-rays induced emission spectra show that, Cs₂LiGdCl₆:10% Ce³⁺ emits into the Ce³⁺ band, spanning from 365 nm to 450 nm wavelengths. Under γ-ray excitation, the sample crystal shows three main decay time components of 129 ns (51%), 573 ns (32%) and 8.9 μs (17%). It offers an energy resolution of 5.0% (FWHM) for the 662 keV full absorption peak at room temperature. We measured an absolute light yield of 20,000 photons/MeV of absorbed γ-ray energy. We found that with a little exposure to the air, the scintillation properties of the Cs₂LiGdCl₆:10% Ce³⁺ crystal deteriorate, which is attributed to the highly hygroscopic nature of this material. We believe that the Cs₂LiGdCl₆:10% Ce³⁺ crystal can be a promising material for medical imaging and radiation detection. Moreover due to the presence of Li and Gd constituents, this scintillation crystal can also be the possible candidate for thermal neutron detection.     

Spectroscopic properties of OH doped and Bi-rich Bi4Ge3O12 crystals by vertical Bridgman method

OH⁻ doped and Bi-rich Bi₄Ge₃O₁₂ (BGO) single crystals were grown by Vertical Bridgman (VB) method. The structure of these crystals was determined by XRD, and the emission spectra in visible and near infrared region (NIR) were measured at room temperature. The emission spectrum of Bi-rich BGO has extra peaks at 385, 367 and 357 nm, Bi-rich BGO after annealing in Ar at 500 °C for 5 h shows a significant emission band peaking around 1170 nm under 808 nm laser diodes (LDs) excitation, and OH⁻ doped BGO shows a noticeable emission band centered at about 1346 nm under 980 nm LDs excitation. A brief discussion is presented.     

Scintillation properties of pure and Ce3+-doped SrF2 crystals

In this paper results of scintillation properties measurements of pure and Ce³⁺-doped strontium fluoride crystals are presented. We measure light output, scintillation decay time profile and temperature stability of light output. X-ray excited luminescence outputs corrected for spectral response of monochromator and photomultiplier for pure SrF₂ and SrF₂-0.3 mol% Ce³⁺ are approximately 95% and 115% of NaI–Tl emission output, respectively. A photopeak with a 10% full width at half maximum is observed at approximately 84% the light output of a NaI–Tl crystal after correction for spectral response of photomultiplier, when sample 10 × 10 mm of pure SrF₂ crystal is excited with 662 keV photons. Corrected light output of SrF₂-0.3 mol% Ce³⁺ under 662 keV photon excitation is found at approximately 64% the light output of the NaI–Tl crystal.     

Energy transfer and excitation wavelength dependent long-lasting phosphorescence in Pr activated Y3Al5O12

Long-lasting phosphorescence (LLP) was observed in Pr³⁺-doped Y₃Al₅O₁₂ (YAG:Pr) after it was excited by 240 or 290 nm light. The photoluminescence (PL) and LLP properties were studied. It is interesting that the PL and LLP spectra were different. In the PL emission spectra both the emissions of d-f and f-f transitions of Pr³⁺ ions were observed. However, in the LLP spectra of YAG:Pr the emissions of d-f transition were absent. It is deduced that the differences were due to the energy transfer process between traps and emission centers. On the other hand, significant differences were observed between the two LLP spectra after the sample was excited by 240 and 290 nm lights, respectively. The thermoluminescence (TL) properties were also studied. It is suggested that these studies will be significant for understanding the mechanism of LLP phenomenon.     

Luminescence characteristics of Pb centres in undoped and Ce-doped Lu3Al5O12 single-crystalline films and Pb→Ce energy transfer processes

At 4.2-350 K, the steady-state and time-resolved emission and excitation spectra and luminescence decay kinetics were studied under excitation in the 2.5-15 eV energy range for the undoped and Ce³⁺-doped Lu₃Al₅O₁₂ (LuAG) single-crystalline films grown by liquid phase epitaxy method from the PbO-based flux. The spectral bands arising from the single Pb²⁺-based centres were identified. The processes of energy transfer from the host lattice to Pb²⁺ and Ce³⁺ ions and from Pb²⁺ to Ce³⁺ ions were investigated. Competition between Pb²⁺ and Ce³⁺ ions in the processes of energy transfer from the LuAG crystal lattice was evidenced especially in the exciton absorption region. Due to overlap of the 3.61 eV emission band of Pb²⁺ centres with the 3.6 eV absorption band of Ce³⁺ centres, an effective nonradiative energy transfer from Pb²⁺ ions to Ce³⁺ ions takes place, resulting in the appearance of slower component in the luminescence decay kinetics of Ce³⁺ centres and decrease of the Ce³⁺-related luminescence intensity.     

Crystal field energy levels of the laser crystal Gd3Ga5O12: Nd

The crystal field energy levels of laser crystal Gd₃Ga₅O₁₂: Nd³⁺ are calculated using the diagonalization (of energy matrix) method. From the calculations, the 93 observed crystal field energy levels are explained reasonably and the root-mean-square (r.m.s.) deviation σ(≈25.6 cm⁻¹) and the scalar crystal-field strength parameter Nv (≈3847 cm⁻¹) are obtained. The results are discussed.     

Timing characteristics of the scintillation response of Gd3Al2Ga3O12:Ce and Gd3Al2.6Ga2.4O12:Ce single crystal scintillators

The timing characteristics of scintillation response of Czochralski-grown Gd₃Al₂Ga₃O₁₂:Ce and Gd₃Al_2.6Ga_2.4O₁₂:Ce single crystals were compared. The photoelectron yield, scintillation decay times, and coincidence time resolution were measured. At 662 keV γ-rays, the photoelectron yield of 6200 phe MeV⁻¹ obtained for Gd₃Al₂Ga₃O₁₂:Ce is higher than that of 4970 phe MeV⁻¹ obtained for Gd₃Al_2.6Ga_2.4O₁₂:Ce, while an inferior energy resolution of the former (7.2% vs. 5.6%) is observed. Scintillation decays are approximated by sum of exponentials with the dominant fast component decay time and its relative intensity of 89 ns (73%) for Gd₃Al₂Ga₃O₁₂:Ce and 136 ns (69%) for Gd₃Al_2.6Ga_2.4O₁₂:Ce. The coincidence time resolution obtained for Gd₃Al₂Ga₃O₁₂:Ce is superior than that of Gd₃Al_2.6Ga_2.4O₁₂:Ce. The normalized time resolution was also discussed in terms of a number of photoelectrons and decay characteristics of the light pulse.     

The optical properties and laser characteristics of Cr and Nd co-doped Y3Al5O12 ceramics

We have fabricated Cr³⁺ and Nd³⁺ co-doped YAG (Cr;Nd:YAG) ceramics, and investigated their optical properties and laser characteristics. The Cr;Nd:YAG has two broad absorption bands at around 440 nm (⁴A₂→⁴T₁) and 600 nm (⁴A₂→⁴T₂) respectively, caused by Cr³⁺ ions. In the case of pumping at 440 nm, the maximum effective lifetime of the Cr;Nd:YAG was 737 μs with a 0.1 at% Cr³⁺ and 1.0 at% Nd³⁺ co-doped YAG sample. Cr³⁺ ions take a role of an effective sensitizer to convert the UV light of flashlamp. For single-shot laser operation, a 10.4 J output energy at 1064 nm was obtained with 0.1 at% Cr³⁺ and 1.0 at% Nd³⁺ co-doped YAG ceramic rod with a laser efficiency of 4.9%. The laser efficiency was found to be more than twice that of a 1.0 at % Nd³⁺:YAG ceramic rod.     

Gadolinium pyrosilicate single crystals for gamma ray and thermal neutron monitoring

Bulk Gd₂Si₂O₇:Ce (GPS:Ce) single crystals obtained by Czochralski method demonstrate a high light output at γ-irradiation (3.8 times higher in comparison with Bi₄Ge₃O₁₂ (BGO)), energy resolution 13% (137Cs, 662 KeV), fast decay time (41.7 ns), and good thermal stability of light output (up to 425 K). This combination of characteristics makes this scintillator very attractive for medical imaging and high-temperature applications. Light output at thermal neutron monitoring is evaluated as twice higher in comparison with Gd₂SiO₅:Ce (GSO). The observed rather high afterglow level (0.2% after 20 ms) and moderate energy resolution (13%) certifies a room for improvement of these parameters by further optimization of crystal quality.     

Crystal growth and characterization of CsSr1–xEux I3 high light yield scintillators

In this work, we report on single crystal growth and characterizations of a new scintillation material: CsSr_1–xEu_x I₃ (0 ≤ x ≤ 1). Single crystals of CsSr_0.99Eu_0.01I₃, CsSr_0.92Eu_0.08I₃ and CsEuI₃ were grown via the Vertical Gradient Freeze method. The crystals exhibit good crystal quality, high light yield, and excellent energy resolution. Initial results show that the scintillation light yield of our CsSr_0.92Eu_0.08I₃ crystal is ～65,000 ph/MeV with 5.9% energy resolution at 662 keV. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Improvement of the scintillation properties of Gd3Ga3Al2O12:Ce,B single crystals having tailored defect structure

A novel approach is reported to minimize various defect centers in Ce doped Gd₃Ga₃Al₂O₁₂ single crystals to improve the scintillation properties. The crystals of Gd₃Ga₃Al₂O₁₂ codoped with 0.2 at% Ce and B (GGAG:Ce,B) have been grown in air and argon ambient using the Czochralski technique. The scintillation light output of crystals grown in Ar ambient was significantly increased after annealing the crystals in air. The measured light output of 60000 ph/MeV for annealed crystals is the highest value reported among this class of materials. As a consequence, the energy resolution at 662 keV gamma‐rays from a ¹³⁷Cs source was improved from 8% for the crystals grown in air to 6% for crystals grown in Ar and subsequently annealed in air. Further, the thermal quenching energy of photoluminescence (PL) emission was increased to be 470 meV for the annealed crystals. The thermoluminescence (TL) measurements suggest that the crystals grown in Ar ambient and post‐growth annealed in air may have a lesser concentration of trap centers which subsequently lead to the improvement in optical and scintillation properties leading to a superior detector performance. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Nd-doped Lu3Al5O12 single-crystal scintillator for X-ray imaging

The optical and scintillation properties of Nd-doped Lu₃Al₅O₁₂ (Nd:LuAG) crystals grown by the Czochralski (Cz) method were examined under X-ray excitation. Their applicability for X-ray imaging was also inspected. The radioluminescence spectrum induced by X-rays showed a broad host emission and sharp Nd³⁺ 4f–4f emission peaks in the UV to visible wavelengths. The light output current of the Nd:LuAG was 85% of that of a standard CdWO₄ X-ray scintillator. The afterglow value measured 20 ms after X-ray irradiation was 1.5%. An X-ray radiographic image was successfully obtained using the Nd:LuAG scintillator coupled with the charge coupled device (CCD) photodetector.     

Luminescence and scintillation properties of Lu0.8Gd1.2SiO5:Ce and Lu1.8Gd0.2SiO5:Ce single crystals: A comparative study

The luminescence and scintillation properties of Lu_0.8Gd_1.2SiO₅:Ce and Lu_1.8Gd_0.2SiO₅:Ce single crystals are compared. At 662 keV γ-rays, light yield (LY) value of 29,800 ph/MeV obtained for Lu_1.8Gd_0.2SiO₅:Ce is much higher than that of 20,200 ph/MeV obtained for Lu_0.8Gd_1.2SiO₅:Ce. The energy resolution of 6.0% obtained for Lu_0.8Gd_1.2SiO₅:Ce is better than that of 7.7% for Lu_1.8Gd_0.2SiO₅:Ce due to its better intrinsic resolution and proportionality of LY. The LY and energy resolution for α-rays, as well as a LY ratio under excitation with α- and γ-rays (α/γ ratio) are also determined. The intrinsic LY and light loss coefficient under excitation with α- and γ-rays are evaluated. The photofraction at 662 keV γ-rays is also determined and discussed.     

Scintillation timing characteristics of (La,Gd)2Si2O7:Ce and Gd2SiO5:Ce single crystal scintillators: A comparative study

The scintillation timing characteristics of (La,Gd)₂Si₂O₇:Ce (GPSLa23.5%:Ce) single crystal were studied and compared with Gd₂SiO₅:Ce (GSO:Ce) single crystal. The photoelectron yield, scintillation decay times and coincidence time resolution were measured. At 511 keV γ-rays, the photoelectron yield of 10,770 ± 500 phe MeV⁻¹ and energy resolution of 5.4 ± 0.2% obtained for GPSLa23.5%:Ce are much better than those of 3350 ± 160 phe MeV⁻¹ and 7.8 ± 0.3% obtained for GSO:Ce. The scintillation decay time profile was measured by the time-correlated single photon counting technique using a fast-slow coincidence setup. In both materials the comparable rise times of several nanoseconds are present. The fast component decay time of 56 ns with relative intensity of 49% obtained for GPSLa23.5%:Ce is inferior to that of 32 ns(88%) obtained for GSO:Ce. Consequently, the coincidence time resolution of GPSLa23.5%:Ce is slightly worse than that of GSO:Ce. The normalized time resolution was also discussed in terms of a number of photoelectrons and decay time of the scintillation pulse.     

Optical characteristics of Cr and Nd codoped Y3Al5O12 ceramics

The optical characteristics of Cr³⁺ and Nd³⁺ codoped Y₃Al₅O₁₂ (YAG) ceramics are measured. These measurements are done using two pumping sources, a 808 nm laser diode (LD) and a Xe short-arc lamp, to simulate solar radiation. The specimens used are 0.1%Cr³⁺/1.0%Nd³⁺ and 3.0%Cr³⁺/1.0%Nd³⁺ (atomic%) codoped YAG ceramics. A Nd:YAG crystal doped with 1.0%Nd³⁺ is used as a reference. The saturation intensities of the Cr/Nd:YAG ceramics pumped by the LD are the same as that of the Nd:YAG crystal, while they are higher when they are pumped by the Xe lamp. The saturation intensities are for the 0.1% Cr-doped ceramic and for the 3.0%Cr-doped ceramic. The small signal gains of the 0.1%Cr-doped and 3.0%Cr-doped ceramics are measured and found to be 1.8 times and 7.0 times higher than that of Nd:YAG for the same intensity of solar pumping, respectively. The quantum efficiency of energy transfer from Cr³⁺ to Nd³⁺ is estimated to be 0.88±0.09 for the 0.1%Cr-doped ceramic and 0.67±0.08 for the 3.0%Cr-doped ceramic.