Karol Bartosiewicz

We present an optimized hot-zone design for the micro-pulling-down method enabling rapid preparation of glass composite rods with embedded Y ₃ Al ₅ O ₁₂ :Ce (YAG:Ce) micro particles.

Fast scintillators are essential for advanced X‐ray imaging and time‐of‐flight techniques. Although stabilizing Ce ⁴⁺ ions in garnet hosts is an effective strategy for suppressing the afterglow and accelerating scintillation, it often introduces quenching pathways that reduce the light yield. This study demonstrates that synergistic host‐dopant engineering in Mg ²⁺ co‐doped Y ₃ (Al,Ga) ₅ O ₁₂ :Ce enables controlled Ce ⁴⁺ ‐ion stabilization and reveals a strong Ga‐dependent efficiency of Ce ³⁺ to Ce ⁴⁺ conversion. The X‐ray absorption near edge structure spectroscopy results indicate Ce ⁴⁺ fractions of 64% and 25% in Y ₃ Al ₃ Ga ₂ O ₁₂ :Ce,Mg and Y ₃ Al ₂ Ga ₃ O ₁₂ :Ce,Mg, respectively. Moreover, vacuum–UV spectroscopy demonstrates that Ce ⁴⁺ ions strongly suppress trap‐mediated energy transfer to the Ce ³⁺ fraction, indicating a redistribution of carrier capture away from defect‐related pathways. This valence state control yields an accelerated scintillation response (30–50 ns), representing a 7.1‐ and 3.6‐fold increase in light yield for Y ₃ Al ₃ Ga ₂ O ₁₂ and Y ₃ Al ₂ Ga ₃ O ₁₂ respectively, and > 10 ² reduction in the afterglow. The X‐ray imaging of biological specimens and electronic components demonstrates an improvement in spatial resolution relative to a standard Lu ₃ Al ₅ O ₁₂ :Ce scintillator. These results establish Ce charge‐state engineering as a composition‐sensitive design principle for achieving superior garnet scintillators with both fast response and high light output.

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.

Long-wavelength mechanoluminescent (ML) materials that convert mechanical stimuli into light hold promise for biomedical imaging and wireless sensing but are often restricted by low brightness and shallow tissue penetration. Here, a heterojunction engineering strategy is employed to enhance near-infrared ML emission in LiGa5O8/Ga2O3:Cr3+ composites, achieving a 416% intensity increase compared with the single-phase LiGa5O8. Incorporation of Ga2O3 introduces deeper electron traps and strengthens the crystal field around Cr3+ centers, thereby boosting emission efficiency in the 700–750 nm range. Density functional theory calculations reveal that orbital hybridization at the interface lowers recombination barriers and promotes radiative transitions. The optimized composite shows excellent aqueous stability over 240 h, while the flexible films fabricated with polydimethylsiloxane enable effective ML imaging through biological tissue, as verified using chicken joints. These findings demonstrate a promising pathway toward high-performance near-infrared ML materials for in vivo monitoring, biomedical imaging, wireless sensing, and intelligent sensing applications.

The exposure of luminescent materials to X-ray radiation and high-power laser excitation results in significant heating, leading to thermal quenching and a corresponding reduction in phosphor efficiency.

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.

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.

This study explored the influence of Sc3+ ions incorporation on the structural, vibrational, luminescent, and scintillation properties of Pr3+-doped Lu3(Al, Sc)2.5Ga2.5O12 garnet crystals. Addressing the limited research on Sc-admixed and Pr3+ doped garnet systems, this work successfully demonstrated the crystallization of garnet crystals from the melt, overcoming the substantial atomic mismatch between Sc and Al while preserving the thermodynamic stability of the garnet phase. Importantly, Sc-admixing enhanced atomic homogeneity and allowed for increased doping concentrations of Pr3+ ions, which is crucial for tailoring the functional properties of advanced optical materials. The trap depths ranged from 1.63 eV (deep traps) to 0.22 eV (shallow traps) across all samples, with frequency factors predominantly between 1 × 107 and 1 × 1011 s–1, consistent with first-order thermoluminescent kinetics. From a materials design perspective, Sc3+ ions substitution induced beneficial host lattice disorder, enhancing the emission intensity of 4f15d11 → 4f2 interconfigurational and 4f2 → 4f2 intraconfigurational transitions. This effect highlighted the potential of Sc as a promising substituent for enhancing the luminescence intensity of rare earth elements. Synchrotron radiation experiments provided insights into the impact of Sc on band gap energy and energy transfer efficiency toward Pr3+ ions offering new opportunities for engineering scintillators and phosphors with tunable optical properties.