Photoluminescence and Scintillation Mechanism of CsPbBr.

Small bandgap scintillators have gained significant attention in recent years. Especially CsPbBr is an interesting material, mitigating the small Stokes shift-related problem of perovskites like CsPbBr. In this work, optical and scintillation properties of CsPbBr single crystals are investigated as a function of temperature, with a detailed focus at 10 K.

Scintillation and Optical Characterization of CsCuI Single Crystals from 10 to 400 K.

Currently only Eu-based scintillators have approached the light yield needed to improve the 2% energy resolution at 662 keV of LaBr:Ce,Sr. Their major limitation, however, is the significant self-absorption due to Eu. CsCuI is an interesting new small band gap scintillator.

Cationic Effects on Photo- and X-ray Radioluminescence of KRE(PO):Ce/Pr (RE = La, Gd, and Y) Phosphors toward X-ray Detection.

Cationic tuning for lanthanide (Ce/Pr)-activated inorganic phosphors with stable, efficient, and fast-decay 5d-4f emissions has emerged as an important strategy toward the continuing pursuit of superior scintillators. The in-depth understanding of the cationic effects on photo- and radioluminescence of lanthanides Ce and Pr centers is requisite for the rational cationic tuning. Here, we perform a systematic study on the structure and photo- and X-ray radioluminescence properties of KRE(PO):Ce/Pr (RE = La, Gd, and Y) phosphors to elucidate the underlying cationic effects on their 4f-5d luminescence.

Avoiding concentration quenching and self-absorption in CsEuX (X = Br, I) by Sm doping.

The benefits of doping CsEuBr and CsEuI with Sm are studied for near-infrared scintillator applications. It is shown that undoped CsEuI suffers from a high probability of self-absorption, which is almost completely absent in CsEuI:2% Sm. Sm doping is also used to gain insight in the migration rate of Eu excitations in CsEuBr and CsEuI, which shows that concentration quenching is weak, but still significant in the undoped compounds.

VUV-UV-vis photoluminescence, X-ray radioluminescence and energy transfer dynamics of Ce and Eu in SrMgSiO.

Ce and Eu doped and Ce-Eu co-doped SrMgSiO phosphors are prepared a high-temperature solid-state reaction technique. The synchrotron radiation vacuum ultraviolet-ultraviolet (VUV-UV) excitation and ultraviolet-visible (UV-vis) emission spectra of diluted Ce and Eu doped SrMgSiO samples are measured at cryogenic temperatures. The electron-vibrational interaction (EVI) between Ce and its surroundings is analyzed.

Temperature dependent scintillation properties and mechanisms of (PEA)PbBr single crystals.

In this work the scintillation properties of PEAPbBr are studied as function of temperature, accessing the potential use of these materials for low temperature applications. The scintillation properties and mechanism have been studied using a combination of temperature dependent photoluminescence emission and excitation, X-ray excited emission and decay measurements. At room temperature the X-ray excited emission is dominated by the 442 nm emission with a lifetime of 35.

Experimental and Theoretical Studies of the Site Occupancy and Luminescence of Ce in LiSr(BO) for Potential X-ray Detecting Applications.

Ce-doped LiSr(BO) phosphors have been prepared by a high-temperature solid-state reaction method, and structural refinement of the host compound has been performed. The excitation and emission spectra in the vacuum ultraviolet-ultraviolet-visible range at cryogenic temperatures reveal that Ce ions preferentially occupy eight-coordinated Sr sites in LiSr(BO). Such experimental attribution is well corroborated by the calculated 4f-5d transition energies and defect formation energies of Ce ions at two distinct Sr sites in the first-principles framework.

Structure, luminescence of Eu and Eu in CaMgSiO and their co-existence for the excitation-wavelength/temperature driven colour evolution.

Luminescent materials with controllable colour evolution features are demanded for the development of multi-level anti-counterfeiting technologies. Here we report the structural and luminescence properties of CaMgSi2O6:Ln (Ln = Eu2+, Eu3+, Eu2+/3+) samples in detail and reveal their excitation-wavelength/temperature driven colour evolution characteristics. By tuning either the excitation-wavelength (276, 304, 343, 394 nm) or temperature (in the 330-505 K range), the designed samples with co-existing Eu2+/Eu3+ ions can achieve diverse and controllable colour evolution from red, to pink, purple and blue.

Site Occupancies, VUV-UV-vis Photoluminescence, and X-ray Radioluminescence of Eu-Doped RbBaPO.

RbBaPO:Eu phosphors have been prepared by a high-temperature solid-state reaction method, and the structure was determined by Rietveld refinement based on powder X-ray diffraction (P-XRD) data. Their VUV-UV-vis photoluminescence properties are systematically investigated with three objectives: (1) based on low-temperature spectra, we clarify the site occupancies of Eu, and demonstrate that the doublet emission bands at ∼406 and ∼431 nm originate from Eu in Ba [Eu(I)] and Rb [Eu(II)] sites, respectively; (2) an electron-vibrational interaction (EVI) analysis is conducted to estimate the Huang-Rhys factors, the zero-phonon lines (ZPLs) and the Stokes shifts of Eu in Rb and Ba sites; (3) the studies on luminescence decay of Eu(I) reveal that dipole-dipole interaction is mainly responsible for the energy transfer from Eu(I) to Eu(II), and the energy migration between Eu(I) is weak. Finally, the X-ray excited luminescence (XEL) spectrum indicates that the light yield of the sample RbBaEuPO is ∼17 700 ph/MeV, showing its potential application in X-ray detecting.

Impacts of 5d electron binding energy and electron-phonon coupling on luminescence of Ce in LiY(BO).

In this work, the crystal structure and electronic structure as well as the synchrotron radiation vacuum ultraviolet-ultraviolet-visible (VUV-UV-vis) luminescence properties of LiY(BO) (LYBO):Ce phosphors were investigated in detail. The Rietveld refinement and DFT calculation reveal the 2/ monoclinic crystal phase and the direct band gap of the LYBO compound, respectively. Only one kind of Ce 4f-5d transition is resolved in terms of the low temperature VUV-UV excitation, UV-vis emission spectra and luminescence decay curves.

Luminescence and Energy Transfer between Ce and Pr in BaYSiO under VUV-vis and X-ray Excitation.

A detailed investigation on photoluminescence properties and energy transfer (ET) dynamics of Ce, Pr-doped BaYSiO is provided along with the potential X-ray excited luminescence application. The luminescence properties of Pr are studied in VUV-UV-vis spectral range at low temperature, and the spectral profiles of PrP and D emission lines are determined using time-resolved emission spectra. Upon 230 nm excitation, the electron population from Pr 4f5d state to its 4f excited state is discussed in detail.

Insight into Eu redox and Pr 5d emission in KSrPO by VRBE scheme construction.

A series of Ln-doped KSrPO (Ln = Ce, Eu, Eu, Pr) phosphors are prepared through a high-temperature solid-state method. The KSrPO compound is confirmed to possess a β-KSO structure with the Pnma group by Rietveld refinement, and the temperature-dependent lattice parameters are investigated with the powder X-ray diffraction results at different temperatures. Ce and Eu ions are introduced to probe the crystal field strength (CFS) and the lanthanide site symmetry by using VUV-UV-vis spectroscopy.

The Effect of Sr on Luminescence of Ce-Doped (Ca,Sr)AlSiO.

A series of Ce-doped (Ca,Sr)AlSiO phosphors with different Ce and Ca/Sr concentrations were prepared by a high temperature solid-state reaction technique. To get insight into the structure-luminescence relationship, the impact of incorporation of Sr on structure of (Ca,Sr)AlSiO was first investigated via Rietveld refinement of high quality X-ray diffraction (XRD) data, and then the VUV-UV excitation and UV-vis emission spectra of (Ca,Sr)AlSiO:Ce were collected at low temperature. The results reveal that the crystal structure evolution of (Ca,Sr)AlSiO:Ce has influences on band gaps and Ce luminescence properties including 4f-5d (i = 1-5) transition energies, radiative lifetime, emission intensity, quantum efficiency, and thermal stability.

Charge Carrier Trapping Processes in REOS (RE = La, Gd, Y, and Lu).

Two different charge carrier trapping processes have been investigated in REOS:Ln (RE = La, Gd, Y, and Lu; Ln = Ce, Pr, and Tb) and REOS:M (M = Ti and Eu). Cerium, praseodymium and terbium act as recombination centers and hole trapping centers while host intrinsic defects provide the electron trap. The captured electrons released from the intrinsic defects recombine at Ce, Pr, or Tb via the conduction band.

Luminescence and X-ray absorption studies on 0.5% Ce(3+) doped BaCa2MgSi2O8 phosphor.

0.5% Ce(3+) doped BaCa2MgSi2O8 phosphor was prepared by a conventional solid state reaction method. Luminescence spectra as well as fluorescence decay were monitored in the VUV-UV range.

Low-temperature VUV photoluminescence and thermoluminescence of UV excited afterglow phosphor Sr3AlxSi1-xO5:Ce(3+),Ln(3+) (Ln = Er, Nd, Sm, Dy and Tm).

Low-temperature (10 K) photoluminescence excitation and emission spectra of undoped Sr3SiO5 as well as Ce(3+) and Eu(3+) single doped Sr3SiO5 have been investigated. They show the host exciton band and the O(2-) to Eu(3+) charge transfer band at 5.98 eV (207 nm) and 3.

The in vivo activation of persistent nanophosphors for optical imaging of vascularization, tumours and grafted cells.

Optical imaging for biological applications requires more sensitive tools. Near-infrared persistent luminescence nanoparticles enable highly sensitive in vivo optical detection and complete avoidance of tissue autofluorescence. However, the actual generation of persistent luminescence nanoparticles necessitates ex vivo activation before systemic administration, which prevents long-term imaging in living animals.

The electronic level structure of lanthanide impurities in REPO4, REBO3, REAlO3, and RE2O3 (RE = La, Gd, Y, Lu, Sc) compounds.

The vacuum referred binding energies of electrons in divalent and trivalent lanthanide impurity states and host band states in the rare earth (RE = La, Gd, Y, Lu, Sc) orthophosphates REPO4, orthoborates REBO3, aluminum perovskites REAlO3, and sesqui-oxides RE2O3 have been determined by combining the recently developed chemical shift model with spectroscopic data from the archival literature. The main trends in impurity and host band level locations with changing type of RE, which determines the site size, and with changing P, B, Al, or RE cation, which determines the strength of bonding with the oxygen ligands, are identified. Sc(3+)-based compounds are characterized by a relatively low energy for the conduction band bottom, or equivalently a high electron affinity, which is attributed to a relatively strong electron bonding in the 3d-shell of Sc(2+).

Experimental comparison of high-density scintillators for EMCCD-based gamma ray imaging.

Detection of x-rays and gamma rays with high spatial resolution can be achieved with scintillators that are optically coupled to electron-multiplying charge-coupled devices (EMCCDs). These can be operated at typical frame rates of 50 Hz with low noise. In such a set-up, scintillation light within each frame is integrated after which the frame is analyzed for the presence of scintillation events.

Electron transfer process between Ce3+ donor and Yb3+ acceptor levels in the bandgap of Y3Al5O12 (YAG).

Thermoluminescence (TL) properties of Ce(3+) and Yb(3+) co-doped in Y(3)Al(5)O(12) (YAG) were studied with the aim of determining the location of energy levels of Ce(3+) and Yb(2+) relative to the bottom of the conduction band (CB) and the top of the valence band (VB) of YAG. The TL glow peak at about 180 °C when heating rate β = 1°C s(-1) was assigned to electron release from Yb(2+), indicating that Yb(3+) acts as an electron trap. The trap depth, which is the depth of the ground-state level of Yb(2+) below the bottom of the CB, was derived from the temperatures of the maximum of the TL glow peak at different heating rates.

Nonproportional response of LaBr3:Ce and LaCl3:Ce scintillators to synchrotron x-ray irradiation.

The nonproportional scintillation response of LaBr(3) doped with 5% Ce(3+) and of LaCl(3) doped with 10% Ce(3+) was measured using highly monochromatic synchrotron irradiation. To estimate the photon response, pulse height spectra at many finely spaced energy values between 9 and 100 keV were measured. The experiment was carried out at the X-1 beamline at the Hamburger Synhrotronstrahlungslabor (HASYLAB) synchrotron radiation facility in Hamburg, Germany.

Luminescence dynamics in Tb(3+)-doped CaWO(4) and CaMoO(4) crystals.

Single crystals of CaWO(4) and CaMoO(4) doped with Tb(3+) have been grown by the flux growth method. Their luminescence properties have been investigated in the 10-600 K temperature range under different experimental conditions. In spite of very similar spectra at low temperature upon excitation at 365 nm, the crystals show a very different behavior as the temperature is raised or the excitation wavelength is changed.

Lanthanide 4f-level location in AVO(4):Ln(3+) (A = La, Gd, Lu) crystals.

The spectral properties of LaVO(4), GdVO(4) and LuVO(4) crystals doped with Ce(3+), Pr(3+), Eu(3+) or Tb(3+) have been investigated in order to determine the position of the energy levels relative to the valence and conduction bands of the hosts along the trivalent and divalent lanthanide series. Pr(3+) and Tb(3+) ground state levels are positioned based on the electron transfer energy from those states to the conduction band, the so-called intervalence charge transfer (IVCT). This approach is compared with an alternative model that is based on electron transfer from the valence band to a lanthanide.