Marcin Eugeniusz Witkowski

Controlled melt nonstoichiometry was investigated as a processing parameter governing secondary-phase formation and functional properties of Ce3+-doped (Tb,Y)3Al5O12 single crystals grown by micropulling-down. Crystals were grown from melts with 0, 3, 6, 9, and 11 mol % Y2O3 deficiency. X-ray diffraction, electron probe microanalysis, and Raman spectroscopy revealed phase-pure garnet up to 3 mol % deficiency, rim-localized α-Al2O3 inclusions at 6 and 9 mol %, and core-localized perovskite-type inclusions at 11 mol %. Secondary-phase formation modified Tb/Y partitioning in the garnet matrix, affecting Ce3+ emission kinetics, Tb3+↔Ce3+ energy transfer, trap depth, and scintillation properties. The 11 mol % deficient crystal showed the highest thermal stability, with the Ce3+ thermal-quenching onset shifting from 375 to 425 K. The 9 mol % deficient crystal reached a luminous efficacy of 158 lm/W and a scintillation light yield of 33,600 photons/MeV. X-ray radiography using the 9 mol % Y2O3-deficient crystal showed clear images of an SD card. These results indicate that melt nonstoichiometry can tune the balance between photoconversion and scintillation performance in rare-earth garnets.

Thermally activated delayed fluorescence (TADF) offers a powerful route for harvesting triplet excitons in organic scintillators, yet achieving simultaneously small singlet–triplet gaps and efficient spin–orbit coupling (SOC) in rigid molecular crystals remains a fundamental challenge. Here we demonstrate that targeted halogen substitution can activate vibrationally assisted spin‐flip channels that dramatically enhance triplet harvesting in crystalline donor‐acceptor emitters, tailoring them for scintillators with higher light yield and faster response times. Using DMAC‐TRZ derivatives bearing fluorine or chlorine substituents, we combine single‐crystal structural analysis, temperature‐resolved photoluminescence, radioluminescence spectroscopy, and quantum‐chemical calculations to reveal how subtle changes in halogen chemistry control excited‐state dynamics. Fluorination lowers the rISC activation barrier to 7.1 meV, consistent with an almost degenerate emissive singlet–triplet manifold, whereas chlorine additionally introduces dynamic SOC enhancement mediated by Cl‐atom vibrations within the crystal lattice. As a result, the chlorinated crystal exhibits an exceptionally small E _a of 3.9 meV, (sub)microsecond‐scale delayed fluorescence, and a scintillation yield of 26 000 photons MeV ⁻¹ . These results reveal a powerful, targeted approach to achieving near S ₁ ‐T ₁ degeneracy combined with vibrationally activated heavy‐atom effects, enabling high‐performance TADF scintillators in organic crystals.

Effects of Lu3+ admixture on photo- and radioluminescence, as well as on scintillation characteristics, were investigated in Gd3-xLuxAl3Ga2O12:Ce,Mg (x = 0.5, 1, 1.5, 2) scintillation ceramics fabricated via chemical co-precipitation and a combination of oxygen sintering, HIP post-treatment and annealing. The Ce3+ 5d1 → 4f emission in photo- and radioluminescence bands was gradually blue shifted with increasing Lu content due to a decrease in the crystal field splitting of the 5d levels. Furthermore, the thermal ionization activation energy, determined from the temperature-dependent PL decay kinetics, increased with increasing Lu content, leading to higher thermal stability of the Ce3+ centers and increase of light yield value. The onset temperature at 362 K for luminescence quenching was determined from the temperature-dependent photoluminescence kinetics. The GdLu2Al3Ga2O12:Ce,Mg ceramic exhibited the highest light yield value of 11,400 photons/MeV at 662 keV γ rays along with fast scintillation decay times of 26.5 ns (59%) + 58.2 ns (41%), and good time resolution of 249 ps.

A next-generation class of dual-phase, multifunctional photoconversion and thermal sensing materials has been developed using Ce³⁺-doped YAG-YAP eutectic crystals, synthesized via directional solidification at variable rates (0.1-0.9 mm/min) to precisely tailor phase morphology and dopant distribution. Structural and compositional analyses revealed a lamellar microstructure comprising alternating garnet (Y₃Al₅O₁₂, YAG) and perovskite (YAlO₃, YAP) domains, with Ce³⁺ ions preferentially partitioned into the garnet phase at elevated solidification rates. Systematic control of domain sizes was achieved by modulating the growth rate. Slower growth resulted in larger domains that enabled near-complete transmission of blue light through YAP, whereas faster growth produced finer structures that led to increased scattering and absorption of blue light. This morphology-driven optical tunability enabled dynamic control over the correlated color temperature (CCT), ranging from cool to warm white emissions. Beyond structural engineering, the eutectics demonstrated dual-mode thermal sensing via ratiometric luminescence thermometry under both photoluminescence (PL) and X-ray-induced scintillation excitation. Excitation modality significantly affected thermal sensitivity due to distinct charge transport and energy transfer dynamics. Under PL, the relative sensitivity reached 0.47% K^-1, while scintillation-based excitation achieved an enhanced sensitivity up to 1.1% K^-1. Crucially, the scintillation mode permits passive, remote temperature monitoring without external optical excitation, activated solely by ambient ionizing radiation. These capabilities position Ce³⁺-doped YAG-YAP eutectics as promising candidates for advanced thermal sensing in extreme environments, including nuclear reactors, aerospace systems, and high-energy particle detectors.

Controllable doping of hybrid organic-inorganic perovskites (HOIPs) fueled strong interest towards their utilization as a scintillating material. In terms of cationic engineering, tin-mixed halides perovskite (TMHP) is considered as a stronger contender than the conventional hybrid perovskite counterparts. However, the lack of physicochemical alteration via simultaneous A- site and X-site substitution remains unresolved to date. In this work, we tailor both organic ligand and halide mixture of TMHPs to shed some light on their optical and scintillation properties. By introducing three organic ligands, we synthesize phenylmethylammonium (PMA), phenethylammonium (PEA) and phenylpropylammonium (PPA) and retain the Br: I ratio at 3:1. In terms of structural order, we find that the interlayer spacing between the inorganic layers is gradually extended from 9.88 Å for (PMA)₂SnBr₃I, 10.29 Å (PEA)₂SnBr₃I, to 10.06 Å for (PPA)₂SnBr₃I. In combination with geometrical orders organic chain penetration and octahedra distortion angle, we propose a rational design to modulate the absorption, photoluminescence (PL), optical bandgap, and thermal quenching of TMHPs. (PMA)₂SnBr₃I exhibit a fastest decay time (τavg = 1.1 ns) than the (PEA)₂SnBr₃I (τ_avg= 2.51 ns) and (PPA)₂SnBr₃I (τ_avg = 3.54 ns), indicating that TMHPs are promising candidates for scintillator applications. The finding is corroborated by density functional theory to outline the weakened antibonding interaction between I 5p and Sn 5s orbitals upon tailoring the organic ligand of the perovskite. Our attempt demonstrates the importance of cation-engineering in leveraging innovative hybrid perovskites with novel response via rational design.

Substituting Sc ³⁺ for Al ³⁺ in Pr ³⁺ -doped Lu _1.5 Y _1.5 Al _{5− x} Sc _x O ₁₂ crystals enhances the Pr ³⁺ emission across the UV-Vis-NIR spectral range. This enhancement is attributed to an efficient Sc ³⁺ → Pr ³⁺ energy transfer and increased structural disorder.

Scintillators convert high‐energy radiation into detectable photons and play a crucial role in medical imaging and security applications. The enhancement of scintillator performance through nanophotonics and nanoplasmonics, specifically using the Purcell effect, has shown promise but has so far been limited to ultrathin scintillator films because of the localized nature of this effect. This study introduces a method to expand the application of nanoplasmonic scintillators to the bulk regime. By integrating 100‐nm‐sized plasmonic spheroid and cuboid nanoparticles with perovskite scintillator nanocrystals, nanoplasmonic scintillators are enabled to function effectively within bulk‐scale devices. Power and decay rate enhancements of up to (3.20 ± 0.20) and (4.20 ± 0.31) folds are experimentally demonstrated for plasmonic spheroid and cuboid nanoparticles, respectively, in a 5‐mm thick CsPbBr₃ nanocrystal‐polymer scintillator at RT. Theoretical modeling also predicts similar enhancements of up to (2.26 ± 0.31) and (3.02 ± 0.69) folds for the same nanoparticle shapes and dimensions. Moreover, a (2.07 ± 0.39) fold increase in light yield under ²⁴¹Am γ‐excitation is demonstrated. These findings provide a viable pathway for utilizing nanoplasmonics to enhance bulk scintillator devices, advancing radiation detection technology.