5d 4f Research Articles

Novel optical-guiding crystal scintillator composed of an Eu-doped SrI2 core and glass cladding

Scintillators are used not only as single crystals in radiation detection systems but also as arrays, columns, and fibers. In this study, a novel optical-guiding crystal scintillator (OCS) was fabricated using an Eu:SrI2 crystal as the core and borosilicate glass as the cladding. The OCS has an elongated shape and can be flexibly processed like an optical fiber. Furthermore, because inorganic scintillator crystals are used as the core, the OCS has high sensitivity to high-energy radiation, such as γ- and X-ray radiation, unlike plastic scintillators. In this study, by observing the cross section of the fabricated OCS, identifying the crystal structure, and investigating the radioluminescence spectrum under X-ray irradiation, OCS fabrication in accordance with the OCS design specifications was confirmed, and the SrI2 crystal structure and Eu2+ 5d–4f luminescence were maintained. The γ-ray responses, such as light yield and decay time, were also investigated.

The Effect of Different Molar Ratios of CeO2 on Photoluminescence Properties of CeO2/TiO2 Nanoparticles

The CeO2-TiO2 nanoparticles were prepared by a combination of hydrothermal and sol-gel preparation methods. the bond structures and crystal properties of the obtained materials were featured with X-ray diffraction, FTIR, Raman, and Bet analysis; surface morphologies were examined with the help of FESEM and STEM. And finally, the PL properties of the synthesized samples were also examined in this study. The excitation and emission spectra of 0.1 mol% and 0.25 mol% CeO2 doped TiO2 phosphors consist of broad bands in the UV (200–300 nm) region with maxima at 254 nm. The excitation band at 254 nm is defined as the charge transfer band (CTB). In the emission spectra, a broadband located from 400 to 700 nm is related to the 5d-4f (5d1→4f1) transition of Ce3+ in TiO2. According to the PL result, the 5d–4f transition of Ce3+ is heavily dependent on the concentration of Ce3+ in the host crystal TiO2.

Influence of Air Annealing on Optical and Scintillation Properties of YAG:Pr,Ca

Single crystals of yttrium aluminum garnet (YAG) with Pr3+ and Ca2+ ions grown by the vertical Bridgman method are submitted to air anneal. The influence of this process on optical absorption, photo‐, and radioluminescence is investigated in a set of samples with different concentrations of Pr and Ca. Absorption induced by the heat treatment in the 300–600 nm range in YAG:Pr,Ca is discussed, in comparison with that in YAG:Ca crystals. Photo‐ and radioluminescence spectra in as‐grown and air‐annealed samples recorded at room temperature are discussed. The features of emission decrease at 5d–4f and 4f–4f transitions of Pr3+ ions after heat treatment are considered.

Cerium and europium doping of Ruddlesden-Popper aluminate phases and their radioluminescence properties

Although many scintillator detectors with the fast and efficient detection of high-energy radiation are commercially produced, new materials are still of great interest. Oxide matrices doped with ions possessing fast and intense 5d–4f radiative transition are one of the researched groups of materials. So called Ruddlesden–Popper phases are structures combining halite-like and perovskite-like structures. The aluminates subgroup (AII n+1-yAIII y) n+1 Al n O3n+1 has been only rarely studied for scintillation use. These phases are stable oxides with a relatively high density and, moreover, they melt congruently, which enables growth from a melt. In this study, we tested Ce3+- and Eu2+-doped (Sr,Ca)1(Gd,Y) n Al n O3n+1 (n = 1; 2) analogues. The samples were prepared by the chelating sol-gel method combined with the annealing in reducing atmosphere to reduce both ions to the intended valence. After the samples were characterized by X-ray diffraction, radioluminescence was used for the basic study of luminescence behaviour of Ce3+ and Eu2+ ions. While Ce3+-doped samples exhibited the 5d-4f radiative transition, Eu-doped samples manifested only luminescence spectra characteristic for Eu3+ ions.

Neutron detection properties of thermoluminescent Sr2B2O5:Eu ceramics

Thermoluminescent (TL) ceramic materials have been developed for neutron detection on the basis of Eu-doped Sr2B2O5. A photoluminescence emission band at around 360 nm was observed for Sr2B2O5 doped with Eu at 0.1–0.3 mol% with respect to Sr, and is attributed to 5d–4f transition of Eu2+. The emission band was also observed in the TL spectra. TL glow peaks were observed at 340, 400, and 500 K in the TL glow curves after X-ray irradiation, and Sr2B2O5 doped with Eu at 0.2 mol% exhibited the highest TL intensity. After neutron irradiation, a significant difference in the TL intensities was observed between the ceramics containing enriched 10B and 11B owing to the contribution of 10B(n,α)7Li reaction to the observed TL. The difference in the TL intensities linearly increased with neutron fluence of, at least, 107–1011 neutrons cm−2. Hence, we succeeded in the development of TL materials for neutron detection.

Synthesis and Characterization of All‐Inorganic Perovskite CsEuBr3 Single‐Crystal Scintillator

All‐inorganic halide perovskites appear as a promising class of scintillators for radiation detection applications due to their excellent optoelectronic properties. Herein, a self‐activated perovskite CsEuBr3 single crystal is developed as an efficient X‐ and γ‐ray scintillator. Single crystals of CsEuBr3 are grown by the Bridgman method. The phase structure, stability, photophysics properties, and scintillation performance of CsEuBr3 single crystals are studied. Under X‐ray irradiation, its emission peaks at 445 and 510 nm, associated with Eu2+ 5d–4f and defect‐related emission, respectively, are studied. Under 137Cs gamma irradiation, it has a decent light yield of 22 000 ± 2000 photons MeV−1 and an energy resolution of 6.2 ± 0.4% at 662 keV with a scintillation decay of 510 ns.

Photo-induced preparation of Ce-doped terbium aluminum garnet and its luminescent properties

Ce(III) activated terbium aluminum garnet (Tb3Al5O12:Ce, TAG:Ce) powder as a luminescent phosphor was synthesized by the photo-induced method. The irradiation of an aqueous solution containing formate anions and soluble salts of both metal ions by UV light led to the precipitation of an amorphous solid phase. Subsequent heat treatment at 1200 °C resulted in the crystallization of the TAG:Ce phase-pure garnet structure. The structure and morphology of the products were investigated by X-ray powder diffraction (XRPD) and by scanning electron microscopy (SEM). The particle size, evaluated by transmission electron microscopy (TEM), ranges from 50 to 150 nm. The manufactured Ce-doped TAG features intensive luminescence corresponding to Ce(III) 5d–4f transitions at 559 nm. Due to its high density, chemical stability, non-toxic character, and excellent scintillation efficiency, the application of Ce-doped TAG nano-powder in photodynamic therapy and preparation of optical ceramics was suggested.

Luminescence and scintillation properties of Ce-doped calcium hafnate perovskite single crystals

Hafnium-based materials are attractive for a scintillator owing to their high density and effective atomic number. In this study, single crystals of Ce-doped calcium hafnate perovskite (Ce:CaHfO3) were synthesized from a Ca-rich composition, and photoluminescence (PL) and scintillation properties were investigated. The X-ray diffraction patterns revealed that the synthesized single crystals were a single phase of CaHfO3. The Ce:CaHfO3 exhibited blue luminescence at 430 nm and fast decay due to the 5d–4f transition of Ce3+ in both PL and scintillation. From the measurement of pulse height spectra under 137Cs irradiation, the highest light yield of 7800 photons/MeV was observed in the 3% Ce:CaHfO3.

Characterization of imperfections in scintillator crystals using gamma-ray induced positron annihilation lifetime spectroscopy

Gamma-ray-induced positron annihilation lifetime spectroscopy (GiPALS) was used to characterize pristine and codoped Lu3Al5O12 (LuAG) crystals grown using Czochralski (Cz) and micropulling-down (mPD) methods. GiPALS spectra were analyzed using a two-state trapping model. The bulk and defect lifetimes were theoretically calculated based on density functional theory (DFT) using the projector-augmented-wave (PAW) method. The experimentally measured and theoretically calculated bulk lifetimes almost agreed, thereby validating the experiment and simulation. The defect lifetimes almost coincided with positron annihilation lifetimes due to Al monovacancy at the 24d and 16a sites. Li+ and Mg2+ codoping weakened the vacancy-related component, indicating that codoping had effectively reduced the concentration of Al monovacancy. The Ce 5d–4f thermoluminescence (TL) glow curve revealed that Mg2+ codoping had annihilated the trapped electron centers. In contrast, Li+ codoping increased the concentration of interstitial Li+ ion associated trapped electron centers. Ce-L3 X-ray absorption near-edge structure (XANES) spectra demonstrated that Ce4+ ions at the 24c site had compensated for Mg2+ ion charges at the 24d and 16a site. The Ce4+ ions and oxygen vacancies were supposed to compensate for Li+ ion charges at the 24d and 16a sites.

Photoluminescence and scintillation properties of Pr-doped SrLu2O4 single crystals with different concentrations

As an investigation of Lu-based scintillators, the 0.05, 0.1, 0.5, and 1.0% Pr:SrLu2O4 single crystals were synthesized by the floating zone method. Pr:SrLu2O4 exhibited the broad and sharp luminescence peaks due to the 5d–4f and 4f–4f transitions of Pr3+, respectively. Pr:SrLu2O4 showed fast decay time constant of ∼18 ns due to the 5d–4f transition of Pr3+. The 0.05 and 0.1% Pr:SrLu2O4 exhibited clear photoabsorption peak under 137Cs gamma-ray irradiation. The 0.1% Pr:SrLu2O4 exhibited the highest quantum yield, luminescence intensity, and light yield among the samples.

Polychromatic luminescence of LiSr4(BO3)3:Eu2+, Dy3+ persistent phosphors

A long persistent phosphor LiSr4(BO3)3: Eu2+, Dy3+ shows a typical 5d–4f transition of Eu2+ under ultraviolet activation with an emission centered at 632 nm. Herein, the lattice site of Sr2+ is partially replaced with Mg2+ and Ba2+ and co-doping is performed using Eu2+ and Dy3+ to successfully synthesize several LiSr4−xBax(BO3)3:2% Eu2+, Dy3+ and LiSr4−yMgy(BO3)3:2% Eu2+, Dy3+ phosphors with multicolor luminescence using a high-temperature solid-phase approach. When x or y = 0.4, the samples exhibit bright yellow or orange–red luminescence under ultraviolet (UV) excitation, with the emission spectra showing blue (611–632 nm) or red (632–648 nm) shifts, respectively. Such shifts in the peak position are ascribed to the weakened or enhanced crystal field strength. Under UV excitation, an afterglow phenomenon is also observed. The afterglow profiles can be simulated using an empirical double decay model. The LiSr3.76Mg0.2(BO3)3: 2% Eu2+, Dy3+ sample exhibits the best afterglow phenomenon, which is potentially attributed to the formation of numerous electron traps with suitable trap depths after the incorporation of Mg2+ into the phosphor lattice.

Scintillation Properties of Pr-Doped Lanthanum Pyrosilicate Single Crystals

Five samples of lanthanum pyrosilicate (La2Si2O7) single crystals with 0.5–10.0% Praseodymium (Pr)-doping concentrations were synthesized by the floating-zone method. Photoluminescence and scintillation properties of these crystals were investigated in this study for the first time. The multiple emissions from electron transitions of Pr3+ were observed on both a photoluminescence emission map and scintillation spectra, including the desired emission band of Pr3+ 5d–4f transition at 250–310 nm. The major photoluminescence and scintillation decay times were approximately 19 and 26 ns, respectively. When compared with commercial scintillators such as Tl-doped cesium iodide (CsI), the Pr-doped La2Si2O7 samples presented a respectively low afterglow level of 32 ppm after 20 ms of X-ray irradiation. Under 662 keV γ-ray irradiation from 137Cs, the 3.0% Pr-doped La2Si2O7 sample presented a scintillation light yield of 3200 ph/MeV, which was the best value among the tested samples.

RPL properties of samarium-doped CaSO4

Radiophotoluminescence (RPL) properties of Sm-doped CaSO4 for radiation dosimetry applications are reported. The samples with varying Sm concentrations are prepared via the solid-state reaction process. The as-prepared samples show photoluminescence due to typical 4f–f transitions of Sm3+ whereas, after X-ray irradiation, additional emission features appear with a broad band peaking at 630 nm as well as a set of multiple sharp lines across 680–820 nm, which are attributed to the 5d–4f and 4f–4f transitions of Sm2+, respectively. Therefore, the RPL in the present material system relies on the generation of Sm2+ centers. The sensitivity is about 3 times lower than that of Ag-doped phosphate glass, but no fading and build-up of signal are evident even immediately after the irradiation. The signal is reversible by heat-treatment at 500 °C, and is reproducible even after the thermal erasure, especially when the differential signal between pre- and post-irradiation is taken into account.

How to Obtain Anti‐Thermal‐Quenching Inorganic Luminescent Materials for Light‐Emitting Diode Applications

AbstractPhosphor‐converted light‐emitting diode (pc‐LED) has drawn much interest due to the efficient light in solid‐state lighting, backlight display, security, and electronic devices. Thermal quenching (TQ) induced by nonradiative relaxation is one of the vital challenges that limits the widespread use of phosphors. Much efforts are devoted to designing different approaches to solve the emission loss at increasing temperature. Here, the mechanism of TQ and recent advances of anti‐TQ‐phosphor‐involved 5d–4f, 4f–4f, 6p–6s, 3d–3d transitions are discussed. Several important design strategies for anti‐TQ phosphors are summarized as follows: 1) defect engineering; 2) energy transfer; 3) structural modulation; 4) enhancing crystallinity; 5) layer structural design; 6) negative/zero thermal expansion; 7) surface coating and glass technology. Additionally, some future challenges and opportunities in this field are proposed. This review promotes the discovery of novel anti‐TQ phosphor materials for LED applications.

Characterization of CaSiO3:Ce crystals for α- and X-ray detection

CaSiO3 crystals doped with 0.5%, 1.0% and 2.0% Ce were developed using the floating zone method, and the scintillation and thermally-stimulated luminescence (TSL) properties were evaluated. Under X-ray irradiation, the emission peaks due to the 5d–4f transitions of Ce3+ appeared at 360 nm in all the samples. Under 241Am 5.5 MeV α-ray irradiation, a clear full-energy peak appeared in all the samples, and the light yield of the 2.0% Ce doped-sample was 1040 ph/5.5 MeV-α. As a TSL dosimeter, the samples were very sensitive to X-rays and showed a good linear response from 0.1 to 1000 mGy, which was equivalent to the measurable sensitivity of commercial dosimeters for personal dose monitoring.

Insight into mechanical and thermodynamic properties of Al2Si2La and Al2Si2Pr from first-principles calculations

The crystal structures, stability, mechanical behaviors, thermodynamic properties and electronic structures of Al2Si2La and Al2Si2Pr compounds have been investigated by means of first-principles calculations. It is revealed from formation enthalpies that Al2Si2La exhibit much more thermodynamically stability. According to the results of elastic constants, Al2Si2Pr has stronger incompressibility, stronger shape deformation resistance and higher stiffness. It can be concluded from Debye temperature and minimum thermal conductivity that Al2Si2Pr and Al2Si2La exhibit nearly the same thermal conductivity. Electronic structures results demonstrate that the Al–Si bonds in Al2Si2La and Al2Si2Pr are attributed to the hybridization of Al 3s state, Al 3p state and Si 3p state, while RE–Si bonds are the contribution of Si 3p state and La 5d or Pr 4f state in Al2Si2La and Al2Si2Pr, respectively.

Development of Yb2+-doped SrBrI and BaBrI crystalline scintillators

Photoluminescence (PL) and scintillation properties are reported for SrBrI:Yb2+ and BaBrI:Yb2+ crystals grown by a self-seeding solidification method. In both samples, the Yb2 spin-allowed and spin-forbidden 4f135d1 → 4f14 transitions were observed for both PL and scintillation. For scintillation, a single emission band at approximately 460 nm was observed for both samples, which was attributed to the spin-allowed Yb2+ 5d–4f transition. The scintillation decay time constants of SrBrI:Yb2+ and BaBrI:Yb2+ were estimated to be 1.6 and 1.4 μs, respectively. The light yields of SrBrI:Yb2+ and BaBrI:Yb2+ were 20,000 and 28,000–44,000 photons/MeV, respectively. The light yield of 1 mol% Yb2+-doped BaBrI (44,000 photons/MeV) was higher than that of NaI:Tl (40,000 photons/MeV), and the energy resolution of 0.5 mol% Yb2+-doped BaBrI (7.7%) was comparable to that of NaI:Tl (7.5%). BaBrI:Yb2+ has potential for application in pulse-counting mode detectors owing to its high light yields, high energy resolution, moderate scintillation decay time constants with ~1 μs, and low deliquescence.

Evaluation of photoluminescence and scintillation properties of Yb<sup>2+</sup>-doped SrCl<sub>2−</sub><i><sub>x</sub></i>Br<i><sub>x</sub></i> crystals

Photoluminescence and scintillation properties are reported for SrCl2−xBrx:Yb2+ (x = 0, 0.3, 1.4, 1.6, and 2.0) crystals grown by a self-seeding solidification method. SrCl2−xBrx have been reported to crystallize in some structural types with different local site symmetries depending on the Cl/Br ratio. Taking advantage of this property, we can control the crystal structure and the local Yb2+ site symmetry of SrCl2−xBrx:Yb2+ by changing the compositions and investigate the behaviors of the spin-allowed and spin-forbidden transitions dependent on the local site symmetry. For photoluminescence and scintillation, both spin-allowed and spin-forbidden Yb2+ 5d–4f transitions were observed for SrCl2:Yb2+ with local Oh symmetry and SrCl0.4Br1.6:Yb2+ and SrBr2:Yb2+ with local C4h symmetry, whereas only spin-forbidden Yb2+ 5d–4f transition was observed for SrCl1.7Br0.3:Yb2+ and SrCl0.6Br1.4:Yb2+ with local D2h symmetry. The spin-allowed transitions were observed in crystals with higher local site symmetry. Light yields of SrCl2−xBrx:Yb2+ (x = 0, 0.3, 1.4, 1.6, and 2.0) were (21000 to 71000) photons/MeV. Crystals with higher local site symmetry, which showed the spin-allowed transitions, had relatively high light yields. Among them, SrCl0.4Br1.6:Yb2+ showed a light yield of 71000 photons/MeV, which is higher than those of previously reported Yb2+-doped scintillators, for example, SrI2:Yb2+ (56000 photons/MeV) and CsBa2I5:Yb2+ (54000 photons/MeV).

Magnetic and transport properties of the mixed 3d–5d–4f double perovskite Sm2CoIrO6

Iridium-based double perovskites having mixed 3d–5d–4f magnetic sub-lattices are expected to exhibit exotic magnetic phenomenon. In this paper, we report a study of structural, magnetic and transport properties of the mixed 3d–5d–4f double perovskite Sm2CoIrO6 (SMCO), which crystallizes in monoclinic structure with space group P21/n and the crystal symmetry remains same throughout the measured temperature down to 15 K. High resolution synchrotron x-ray diffraction reveals an isostructural phase transition around 104 K. Magnetization measurements on polycrystalline samples indicate that SMCO orders ferrimagnetically at T FiM = 104 K; while, a second transition is observed below 10 K due to the rare-earth (Sm3+) ordering. The ferrimagnetic transition is well-understood by Néel's two-sublattice model, which is primarily ascribed to antiferromagnetic coupling between Co2+ and Ir4+ sub-lattices. Electronic transport measurement shows the insulting behaviour of SMCO, which follows Mott variable-range hopping conduction mechanism. However, dielectric measurements as a function of temperature rules out the presence of magneto dielectric coupling in this compound.

Investigation of SrSiO3:Ce crystals for scintillator application

We developed SrSiO3:Ce crystals with different dopant concentrations of 0.5%, 1.0% and 2.0% using the floating zone method and investigated the scintillation and storage luminescence properties. Under X-ray irradiation, a broad emission band peaking at around 360 nm was observed in all the samples. The decay time constants were in the range of 33–34 ns, which were typical values for the 5d–4f transitions of Ce3+. The 1.0% and 2.0% Ce-doped samples showed a photoabsorption peak under 241Am 59.5 keV γ-rays and the light yield was 1200 and 1400 ph MeV−1, respectively. The results of pulse-height spectra and thermally-stimulated luminescence showed a complementary relationship between scintillation and ionizing-radiation-induced storage luminescence properties in Ce-doped SrSiO3.