Experimental and Theoretical Studies of the Site Occupancy and Luminescence of Ce³⁺ in LiSr₄(BO₃)₃ for Potential X-ray Detecting Applications

Abstract

Ce3+-doped LiSr4(BO3)3 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 Ce3+ ions preferentially occupy eight-coordinated Sr2+ sites in LiSr4(BO3)3. Such experimental attribution is well corroborated by the calculated 4f–5d transition energies and defect formation energies of Ce3+ ions at two distinct Sr2+ sites in the first-principles framework. In addition, the doping concentration-dependent luminescence and the temperature-dependent luminescence are systematically investigated by luminescence intensity and lifetime measurements, respectively. This shows that concentration quenching does not occur in the investigated doping range, but inhomogeneous broadening exists in the concentrated samples. With the estimated thermal quenching activation energy, the discussions on the thermal quenching mechanisms suggest that the thermal-ionization process of the 5d electron is a dominant channel for thermal quenching of Ce3+ luminescence, despite the fact that thermally activated concentration quenching cannot be excluded for the highly doped samples. Finally, the X-ray excited luminescence measurement demonstrates the promising applications of the phosphors in X-ray detection.

VUV-UV-vis photoluminescence, X-ray radioluminescence and energy transfer dynamics of Ce3+ and Eu2+ in Sr2MgSi2O7

“…To estimate the absolute light yield under X-ray excitation of these samples, a BaF 2 crystal is measured under the same experimental conditions. 13 The BaF 2 crystal presents typical self-trapped exciton emission with two bands with their maxima at ∼300 and 220 nm, respectively, and its integrated intensity is specified as 8.80 × 10 3 ph MeV −1 .…”

“…1 due to the auto-ionization processes of electrons in these higher 5d 2,3,4,5 excited states. 13 3. 20,25 In these compounds, there is only one type of eight-fold coordinated Ba 2+ or Sr 2+ site with C 1 symmetry as listed in Table 1.…”

“…To estimate the absolute light yield under X-ray excitation of these samples, a BaF 2 crystal is measured under the same experimental conditions. 13 The BaF 2 crystal presents typical self-trapped exciton emission with two bands with their maxima at ∼300 and 220 nm, respectively, and its integrated intensity is specified as 8.80 × 10 3 ph MeV −1 . The emission spectrum of the Eu 2+ doped sample under X-ray excitation is in good agreement with that under VUV-UV excitation, and a series of extremely weak sharp peaks in the range of 550-750 nm are due to incomplete reduction of Eu 3+ ions, but the XEL spectrum of the Ce 3+ doped sample is somewhat different from the photoluminescence (PL) spectrum.…”

Site Occupancies, Electron–Vibration Interaction and Energy Transfer of CaMgSi2O6: Eu2+, Mn2+ Phosphors for Potential Temperature‐Sensing and Anti‐counterfeiting Applications

“…Besides, the first-principles calculation of the defect formation energies in Table S1 and Figure S5 can also provide theoretical support for this issue, and the more detailed work is under way. [26,27] In the following we deal with the Eu 2 + À Mn 2 + energy transfer.…”

Anomalous Anisotropic Dopant Distribution in Hexagonal Yttrium Sublattice

“…As a complement to experimental characterizations such as high-resolution transmission electron microscopy, first-principles calculations based on density functional theory (DFT) can accurately predict substitution sites in crystal lattices. − Additionally, spectroscopic characterization can be used to probe multipolar interactions between lanthanide ions, which gives information about their distances . Here, by combining DFT calculations with spectroscopy characterization, we demonstrate that Y 3+ ions are preferentially substituted in β-NaYF 4 lattices by light Ln 3+ ions (La 3+ to Sm 3+ ) at low doping concentrations, while heavy Ln 3+ ions (Eu–Lu) show random substitution.…”