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Driven by the pursuit of optimizing the luminescent properties of garnet-based single crystals for X-ray imaging applications, this work reports on the successful synthesis and in-depth characterization of GYAGG crystals doped with Ce³⁺ or Tb³⁺ ions, and doubly-doped with both of them. Micro-pulling down synthesis yielded crystals with a single cubic phase confirmed by X-ray diffraction. Photoluminescence (PL) and radioluminescence (RL) measurements on Ce³⁺,Tb³⁺ co-doped GYAGG revealed bidirectional energy transfer processes. Characteristic broadband 5d 1 →4f emission of Ce³⁺ centers peaking at 530 nm and narrow 4f→4f emission lines of Tb³⁺ ions starting from 5D 4 level within 480–630 nm were observed. At higher doping levels, cross-relaxation in Tb³⁺ pairs resulted depleted 5D 3 state and only the emission from 5D 4 one was observed in the spectra. Analysis of PL decay characteristics corroborated the spectral observations, confirming progressively decreasing Ce³⁺ decay time (down to 40 ns at 15 % Tb3+) due to enhanced Ce³⁺→Tb³⁺ energy transfer. Similarly, the Tb³⁺ decay time accelerated by more than 60 % after the Ce³⁺ co-doping. Notably, co-doping with 0.5 % Ce³⁺ and 10–15 % Tb³⁺ doubled the luminescence intensity of RL spectra compared to 0.5 % Ce³⁺-doping alone, attributed to the increased density of emitting centers. • High-quality and crack-free GYAGG:Ce,Tb single crystals were successfully grown. • The photoluminescence spectra revealed Ce³⁺↔Tb³⁺ bidirectional energy transfer. • At lower Tb³⁺ doping (0.5 %), the bidirectional energy transfer was inefficient. • High Tb³⁺ doping (15 %) significantly enhanced energy transfer. • Co-doping yielded a two-fold radioluminescence intensity compared to sole doping. [ABSTRACT FROM AUTHOR]

Luminescence excitation spectra of BaBrI single crystals doped by divalent lanthanide ions are studied using synchrotron radiation excitations from the MAX IV 1.5 GeV storage ring. The energy of the edge and the formation of core cation exciton as well as the energy threshold of the multiplications of electronic excitations is found. It was clearly established the energy transfer from intrinsic luminescence centers to Sm2+ and Eu2+ ions. [ABSTRACT FROM AUTHOR]

The luminescence and scintillation properties of SrI 2 single crystals doped with 5% Eu2+ and 0.05%, 0.2% and 0.5% Sm2+ are evaluated. X-ray excited and photoluminescence measurements show energy transfer from excited Eu2+ ions to Sm2+ ions. At a concentration of 0.5% Sm2+, the luminescence consists almost entirely of 740 nm emission from Sm2+ 5d-4f transitions. Co-doping SrI 2 :5% Eu2+ with Sm2+ provides a novel method to bypass the self-absorption problem encountered in large SrI 2 :Eu2+ crystals and, at the same time, provides a unique near-infrared emitting scintillator with a light yield of approximately 40,000 photons/MeV. [ABSTRACT FROM AUTHOR]

Photoluminescence and thermally stimulated luminescence of Gd 3 (Ga,Al) 5 O 12 :Ce single crystals and epitaxial films co-doped with different concentrations of Mg 2+ ions are investigated in the 77–500 K temperature range under excitation in the 4f - 5d 1 and 4f - 5d 2 absorption bands of Ce 3+ ions. Influence of Mg 2+ ions on the photoluminescence intensity, spectrum, decay kinetics, temperature dependence of the photoluminescence intensity, and the activation energy of luminescence thermal quenching is observed. Co-doping with Mg 2+ is shown to result in a drastic reduction of the afterglow and thermally stimulated luminescence and in a strong shortening of the afterglow decay kinetics. It influences also defects creation spectra and the activation energy of the photostimulated defects creation. The Mg 2+ - induced changes in the characteristics of the Gd 3 (Ga,Al) 5 O 12 :Ce, Mg single crystals and epitaxial films are found to be strongly different, and possible reasons of these differences are discussed. [ABSTRACT FROM AUTHOR]

The luminescence and scintillation properties of gadolinium terbium aluminium garnet single crystalline films, Gd 3−x Tb x Al 5 O 12 , doped with Ce 3+ are investigated as a function of the Gd/Tb ratio with the aim of an improved understanding of the energy transfer processes between Ce 3+ and Tb 3+ ions in the aluminium garnet hosts. Upon replacing the Gd 3+ by Tb 3+ , the crystal field splitting for the 5d energy level of Ce 3+ does not change significantly, due to comparable sizes of the Gd 3+ and Tb 3+ cations. Temperature dependence of the decay time of Tb 3+ and Ce 3+ luminescence confirms an efficient energy transfer from the Tb 3+ to Ce 3+ and provides a qualitative understanding of this process. Furthermore, bidirectional energy transfer processes between the Ce 3+ and Tb 3+ are revealed. Scintillation decays under α-particles excitation show the presence of the fast and slow sub-microsecond components. [ABSTRACT FROM AUTHOR]

Fast energy transfer from Yb2+ to Sm2+ is a requirement when using Yb2+ as a sensitiser for Sm2+ emission for near-infrared scintillator applications. This cannot be achieved through dipole-dipole interactions due to the spin-forbidden nature of the involved Yb2+ transition, making the rate of energy transfer too slow for application. This work explores whether exploiting the exchange interaction by increasing the Yb2+ concentration to 99% is an effective way to increase the rate at which energy is transferred from Yb2+ to Sm2+. The scintillation characteristics of CsYbBr 3 :1%Sm, CsYbI 3 :1%Sm and YbCl 2 :1%Sm single crystals were studied through 137Cs excited pulse height spectra, X-ray excited decay and X-ray excited luminescence spectra. An energy resolution of 7% and a light yield of 30,000 ph/MeV was achieved with CsYbI 3 :1%Sm. Photoluminescence spectroscopy and decay studies were performed to study the band structure and relaxation dynamics. • Energy transfer from Yb2+ to Sm2+ happens on a subnanosecond timescale. • Detection of 20,000 photons in the 662 keV photopeak for CsYbI 3 :1%Sm. • A 7% energy resolution was achieved with CsYbI 3 :1%Sm. • Sm2+ emission intensity of all samples is stable between 78 K and 700 K. [ABSTRACT FROM AUTHOR]

A novel NIR emitting scintillator with 825 nm was developed by doping Sm2+ in Cs 4 Eu(Br,I) 6 crystal. The single crystals of Cs 4 Eu(Br,I) 6 :Sm were successfully grown by the Bridgman method. The crystal structure and valence state was approved by XRD and XPS methods. The luminescence properties and energy transfer were systematically investigated. The energy transfer mechanism is variable for different Sm2+ concentration. The PL decay profiles show that the Sm2+-related emission has fast decay of nanosecond. The proportion of fast decay can be tunable by adjusting Sm2+ doped concentration. The Sm2+ doped europium -host material will have a potential application for unclear detection as near-infrared (NIR) scintillators. • The novel NIR emitting Cs 4 Eu(Br,I) 6 :Sm scintillation crystals were successfully grown by the Bridgman method and the luminescence properties is tunable. • The proportion of nonradiative energy transfer from Eu2+ to Sm2+ was improved and the PLQY of Sm2+-related is up to 42.1%. • The fast decay time component of Sm2+ (50 ns) is up to 31.8% for Cs 4 Eu(Br,I) 6 : 3 mol%Sm crystal. • The proposed Sm2+ doped europium -host material principle is an effective method to develop near-infrared (NIR) scintillators for nuclear radiation detection. [ABSTRACT FROM AUTHOR]

Multicomponent garnets (Y 3− x Gd x Al 5− y Ga y O 12 ) doped with Ce 3+ ions are promising scintillators with a high density, fast response time and high light yield. To deepen the knowledge about the transfer stage of scintillation mechanism we discuss the energy migration and energy transfer processes in the set of undoped and Ce 3+ activated multicomponent garnet single crystals. Temperature dependence of Gd 3+ emission intensities as well as decay kinetics in Y 3− x Gd x Al 5− y Ga y O 12 ( x , y =1,2,3) crystals point to the Gd 3+ →Gd 3+ nonradiative energy migration, which is diffusion limited. Concentration quenching of Gd 3+ emission occurs by energy migration to accidental impurities and/or structure defects. Temperature dependence of photoluminescence emission intensities and decay time measurements of Gd 3+ as well as Ce 3+ ions in Gd 3 Ga 3 Al 2 O 12 :Ce 3+ single crystal reveal nonradiative energy transfer Gd 3+ →Ce 3+ (including migration through Gd 3+ sublattice) which is responsible for slow Ce 3+ fluorescence decay component. [ABSTRACT FROM AUTHOR]

The nature of luminescence centers in NaI:Eu scintillation crystals was studied in a wide excitation energy and temperature ranges. Radio- and photoluminescence spectra and TSL curves were measured for crystals with varied activator concentrations. Two main narrow luminescence bands at 2.8 eV (center I) and 2.6 eV (center II) were found at 10 К. Center I dominates for low Eu concentration (<0.07%). Increase of activator content leads to suppression of center I emission and enhancement of center II. Presence of oxygen containing impurities in heavily doped crystals is due to high hygroscopicity of the NaI matrix and EuI 2 dopant. Analysis of emission and thermoluminescence features allows justifying the role of anion impurities (oxygen/hydroxyl ions) in formation of activator center II, which is responsible for scintillation efficiency of NaI:Eu crystals at room temperature. [ABSTRACT FROM AUTHOR]

Lanarkite type Pb 2 MoO 5 single crystals were grown using low temperature gradient Czochralski technique and their optical and luminescent properties were studied. The luminescence band at 590–600 nm was observed under UV and X-ray excitations and ascribed to emission of self-trapped excitons. The band is thermally quenched at T > 15 K with the activation energy of process, E act = 11 meV. The measurements of thermostimulated luminescence demonstrated the presence of shallow traps, which adversely influence the energy transfer to the emission centers. [ABSTRACT FROM AUTHOR]

The Nd-doped and Er-doped LuF 3 single crystals were grown by the micro-pulling-down method to study their scintillation properties in the vacuum-ultraviolet (VUV) region. The doubly Nd–Er codoped single crystal was grown to study possibility of scintillation performance improvement by energy transfer from Er 3+ to Nd 3+ ions. The LiF flux was to avoid phase transition below melting temperature. The 1%Nd-doped sample showed the highest overall scintillation efficiency under X-ray excitation which was 7 times as high as that of the LaF 3 :Nd 8% standard. The leading Nd 3+ 5d–4f emission was situated at 176 nm, while the Er 3+ 5d–4f emission for Er-doped samples was observed at 163 nm, which better matches the sensitivity of some VUV-sensitive photodetectors. The optimum Er concentration was determined to be around 1–3 mol%. No Er 3+ 5d–4f emission was observed for the doubly Er,Nd-codoped sample due to energy transfer from the Er 3+ to Nd 3+ ions. Slight improvement of the light yield was observed in the doubly-doped sample with respect to the Nd-only doped one. [ABSTRACT FROM AUTHOR]

Abstract: The work is dedicated to the development of scintillating screens based on the single crystalline films (SCF) of Ce,Tb doped Lu-based silicates, perovskites and garnets grown by the liquid phase epitaxy method. We confirm in this work the presence of the Ce → Tb energy transfer in LSO and LuAP hosts. We also show that in Ce–Tb doped LuAG SCF, the effective Tb → Ce energy transfer is observed. This results in increasing the light yield of the luminescence of double doped LuAG:Ce,Tb SCF up to 25–30% with respect to single Ce doped (Y,Lu)AG SCF counterparts at optimal ratio of Ce/Tb ions. [Copyright &y& Elsevier]

Results of investigation of energy transfer mechanism in SrF2 crystals doped with Pr^3+ ions are presented. Temperature dependences of 5d-4f and exciton emission in this material under X-ray excitation, and thermostimulated luminescence (TSL) in temperature range 80–300 K are studied. It has been established that in SrF2-Pr^3+ crystals the consecutive electron-hole capture mechanism of energy transfer takes place. Also we found that hole centers made a contribution to energy transfer from primary electrons and holes to Pr^3+ ions. [ABSTRACT FROM PUBLISHER]

The luminescence, scintillation, and photoconversion properties of the single crystals of Ce3+ doped Tb 3−x Gd x Al 5-y Ga y O 12 (х = 0–1.5; у = 2–2.5) mixed garnets, grown by the micro-pulling-down (μ-PD) method, are investigated as a function of the Tb/Gd ratio with the aim of development of phosphor-convertors of white LED and scintillators. The partial Tb3+ substitution by Gd3+ cations leads to the suitable change of the crystal field splitting of the 5d energy levels of Ce3 ions due to different sizes of the Gd3+ and Tb3+ cations. For this reason, the cation engineering enables to improve the luminescence and scintillation characteristics of Tb 3−x Gd x Al 3-2.5 Ga 2-2.5 O 12 crystals due to increasing the efficiency of Gd3+→ Tb3+→ Ce3+ cascade energy transfer observed in these solid solutions. We have shown that from all the crystals under study, the Tb 3-x Gd x Al 2.5 Ga 2.5 O 12 :Ce (х = 1–1.5) crystal is the best promising candidate for the photoconversion and scintillation applications. • Single crystals of TbGdAGG:Ce grown by the micro-pulling-down method. • Tb3+/Gd3+ ratio control improving the color rendering and scintillation properties. • The best photoconversion properties are shown by Tb 2-1.5 Gd 1-1.5 Al 2.5 Ga 2.5 O 12 :Ce. [ABSTRACT FROM AUTHOR]

Single crystal of Ce doped Gd 3 Ga 3 Al 2 O 12 is one of the most studied advanced scintillators currently. The scintillation kinetics has been investigated with different excitations. The higher excitation density of alpha particles quenches the scintillation light yield but on the contrary the decay curve gets accelerated with gamma rays unlike that have been typically observed for conventionally used halide scintillators. In view of resolving this unusual behavior, a thorough investigation has been first time performed by carrying out systematic experiments on temperature dependent scintillation properties with gamma and alpha irradiation. The dependence of light yield for both radiations behaves differently with temperature with a notable early onset of quenching for charged particles. All three decay components also behave differently with temperature to indicate the various mechanisms governing the relaxation of excited charged carriers. At some temperatures the decay time components indeed behave in the similar manner as measured for halide crystals. The maximum difference in decay components carrying major amplitude occurs close to room temperatures leading to better discrimination ability. A strong correlation with thermo-luminescence properties has been observed to investigate the role of defect structure. A comprehensive model based on the prominent role of charged carriers released from trap centers along with the energy transfer and migration via Gd sub-lattice in governing the scintillation properties has been convincingly presented. It has demonstrated precisely the unusual behavior of this material but can be extended more considerably to describe various properties of other scintillators as well. • Single crystals of Ce doped Gd 3 Ga 3 Al 2 O 12 were grown by Czochralski method. • The light yield quenches under massive particle radiations but the decay time slows down. • A model is proposed to explain this strike difference from halide scintillator. • Temperature dependent kinetics studied under different radiations. • The role of defect structure and host energy transfer with excitation kinetics for alpha and gamma. [ABSTRACT FROM AUTHOR]