STED properties of Ce^3+, Tb^3+, and Eu^3+ doped inorganic scintillators

Abstract

Scintillator-based X-ray imaging is a powerful technique for noninvasive real-space microscopic structural investigation such as synchrotron-based computed tomography. The resolution of an optical image formed by scintillation emission is fundamentally diffraction limited. To overcome this limit, stimulated scintillation emission depletion (SSED) X-ray imaging, based on stimulated emission depletion (STED) microscopy, has been recently developed. This technique imposes new requirements on the scintillator material: efficient de-excitation by the STED-laser and negligible STED-laser excited luminescence. In this work, luminescence depletion was measured in several commonly-used Ce³⁺, Tb³⁺, and Eu³⁺ - doped scintillators using various STED lasers. The depletion of Tb³⁺ and Eu³⁺ via 4f-4f transitions was more efficient (P_s = 8…19 mW) than Ce³⁺ depletion via 5d-4f transitions (P_s = 43…45 mW). Main origins of STED-laser excited luminescence were one- and two-photon excitation, and scintillator impurities. LSO:Tb scintillator and a 628 nm cw STED-laser is the most promising combination for SSED satisfying the above-mentioned requirements.

Stimulated scintillation emission depletion X-ray imaging

“…5(a). The X-ray excited scintillation signal decreases with increasing STED-laser power, similar to the optically excited luminescence [34]. Remarkably, we did not detect any additional excitation due to possible interaction of STED-laser photons with X-ray absorption products, e. g. conduction band electrons.…”

“…According to Eq. (2), a 2-3 fold resolution improvement can be expected for a 100 mW STED-laser applied to LSO:Tb [34]. Our measured visibility improvement is apparently far from optimum, but it clearly demonstrates the feasibility.…”

“…Its signal is ~60,000 cps using no X-ray pinhole, ~40,000 cps using the 16 μm pinhole, and ~10,000 cps using the 1.8 μm pinhole, corresponding to 67%, 57%, and 25% of the original scintillation signal, respectively. Those fractions are higher than 14% in the case of focused optical laser excitation [34]. The depleted signal, plotted as dotted curves in Fig.…”

“…Typical scintillator screen luminescence centers are Ce 3+ , Tb 3+ , or Eu 3+ lanthanides [13]. The depletion through 4f-4f transitions of Tb 3+ and Eu 3+ require in general lower STED-laser powers compared to 5d-4f transitions of Ce 3+ [34]. Based on Eq.…”

“…The filters were tilted relative to each other to ensure <10 −12 transmittance at 628 nm. Note that LSO:Tb and 628 nm STED-laser were selected out of a number of other combinations, firstly, because the LSO:Tb excitation can be depleted at relatively low power of the 628 nm laser, and secondly, because of sufficiently weak luminescence of LSO:Tb excited by the 628 nm laser itself [34]. STED-laser PSF functions in Fig.…”