Elemental Fluctuation in Gd3Al2Ga3O12:Ce Crystals Imposed by Li+ and Mg2+ Co-Doping: The Impact on Defects, Luminescence, and Scintillation Properties

This research revealed the response of Ga and Al sublattices to the incorporation of mismatching substituents in Gd3Al2Ga3O12:Ce single crystals. Incompatible in size and charge, Li+ and Mg2+ substituents violated configurational entropy. This led to lattice distortion and triggered structural rearrangements. The radial fluctuation of the Ga and Al elements was proven by multi-elemental energy-dispersive X-ray spectroscopy mapping and elemental composition analysis. Further evidence was observed by the shift of the exciton creation energy toward higher energy in the vacuum ultraviolet excitation spectra recorded with synchrotron radiation. In the Li+ and Mg2+ co-doped samples, the crystal core was depleted with Ga atoms and enriched with Al elements. The crystal rim showed the opposite behavior. The change in thermoluminescence peak positions revealed a different mechanism for the formation of localized traps. As a result, Li+ co-doping slightly improved the light yield value, but at the same time decelerated the scintillation decay time. On the contrary, Mg2+ co-doping markedly diminished scintillation parameters

Development of Tb_1.5Gd_1.5Al₅O₁₂:Ce Single-Crystalline Film Converters for WLED Using a Liquid Phase Epitaxy Growth Method

The investigation of the structural, luminescent and photoconversion properties (color coordinates, correlated color temperature, color rendering index and luminous efficacy) of the single-crystalline films of Ce3+-doped Tb1.5Gd1.5Al5O12:Ce mixed garnet with variable film thickness was performed in this work. These film converters were grown on undoped Y3Al5O12 substrates using the liquid phase epitaxy technique. When combined directly with blue LEDs that were commercially available in the market, the developed garnet film converters were responsible for producing white light. The trend line on the color coordinate diagram was obtained for the first time for the Tb1.5Gd1.5Al5O12:Ce converters with the systematic variation in film thickness in the range of 45–82 µm. Under 464 nm blue LED excitation, the investigated converters with a thickness of 55 µm resulted in an ideal white color

Advances in Ce3+ doped Y1±xAlO3 (x≠0) single crystal perovskite scintillators through nonstoichiometric engineering

The influence of nonstoichiometric engineering on the scintillation properties of Ce3+ doped yttrium aluminum perovskite (YAP:Ce) crystals was investigated. Crystals with slight yttrium excess (Y1·004AlO3:Ce), yttrium deficiency (Y0·994AlO3:Ce), and stoichiometric composition (YAlO3:Ce) were synthesized using the micro-pulling down method. Structural characterization confirmed crystallization in the pure orthorhombic Pnma space group for all compositions. Optical absorption spectroscopy revealed an extensive background in the nonstoichiometric crystals due to the increased degree of light scattering centers associated with the defects. The photoluminescence excitation and emission spectra of Ce3+ ions were unaffected by nonstoichiometry. However, the scintillation decay kinetics and light yield exhibited marked improvements in the Y1±xAlO3:Ce (x≠0) crystals. The light yield increased by 22 % and 15 % and the slower component of the decay accelerated from 171 ns to 106 and 131 ns compared to the stoichiometric crystal. Thermoluminescence glow curves revealed that nonstoichiometry significantly altered the concentrations of antisite defects and oxygen vacancies. The EPR spectroscopy investigations revealed a correlation between the Ce3+ ions concentration and the degree of nonstoichiometry. Strategic engineering of nonstoichiometry in Y1±xAlO3:Ce (x≠0) scintillators may have provided an effective approach to optimizing scintillation performance

Luminescent properties of Gd14_{14}Lu0.1_{0.1}Y15_{15}Al5_5O12_{12}:Ce and Gd3_3Ga27_{27}Al2.3_{2.3}O12_{12}:Ce single crystals grown by micro-pulling down technique

The luminescent properties of the single crystals of Ce$^{3+}$ doped (Gd$_{1−x}$−yLuxYy)$_3$Al$_5$O$_{12}$:Ce (x = 0.1; y = 1.5) and Gd$_3$Ga$_x$Al$_{5-x}$O$_{12}$:Ce (x = 2.7) garnets (GLYAG:Ce and GGAG:Ce) were investigated in this work. Both crystals were grown by the micropulling down method. The conventional absorption and luminescence spectral measurements together with the luminescent spectroscopy under excitation by synchrotron radiation were performed to characterize the optical properties of crystals. It has been found that cumulative effects of reducing the ion radius from Gd$^{3+}$ to Y$^{3+}$ and Lu$^{3+}$ in the dodecahedral sites of the garnets host and alloying of Al$^{3+}$ ions in octahedral positions instead Ga$^{3+}$ ions increases the crystal field strength and causes the respective redshift of the Ce$^{3+}$ emission spectra in GLYAG:Ce crystals in comparison with GAGG:Ce garnet. The energy transfer from Gd$^{3+}$ cations to Ce$^{3+}$ has also been registered at the emission spectra and excitation spectra of both crystals. The energies of creation of the excitons bound with the Ce$^{3+}$ ions in GLYAG:Ce and GAGG:Ce hosts were found to be equal to 6.415 ± 0.15 eV and 6.22 ± 0.15 eV, respectively. Both crystals show well-distinguished thermo- and optically stimulated luminescence (TSL and IR OSL) after $α$- and $β$-particle irradiation. Meanwhile, GAGG:Ce crystals show significantly higher TSL and IR OSL intensities (by 3–4 times) and faster OSL decay kinetics in comparison with GLYAG:Ce counterpar

Highly textured lead-free piezoelectric polycrystals grown by the micro-pulling down freezing technique in the BaTiO3 –CaTiO3 system

International audienceHighly textured cm-sized (Ba1−xCax)TiO3 (x = 0.05) polycrystals at off-eutectic composition were grown by the micro-pulling down freezing technique from a BaTiO3–CaTiO3 system at a high pulling velocity of about 48 mm h−1. Textured polycrystals exhibiting submillimetre-sized dendrites along the (110)pc growth direction and geometrical grains along the (100)pc direction were revealed by a complementary analysis performed by Laue diffraction and EBSD techniques. An average Ca content of about x = 0.0435 was measured throughout the whole volume of the boule and led to an effective partition coefficient of Ca of about 0.87. LIBS measurements highlighted the local segregation of Ca and major impurity contents within dendrites, grains and at the grain boundaries. Dielectric and piezoelectric measurements performed on oriented polycrystalline textured samples led to Curie temperatures up to 116 °C and d33 up to 214 pC N−1, in very good agreement with literature values. Both chemical and physical results obtained in the BCT system make the μ-PD technique a promising and alternative way to improve the piezoelectric response of lead-free solid solution-based crystals through their texturing along preferential crystallographic directions

Micro-Inclusion Engineering via Sc Incompatibility for Luminescence and Photoconversion Control in Ce³⁺-Doped Tb₃Al_5−xSc_xO₁₂ Garnet

Aluminum garnets display exceptional adaptability in incorporating mismatching elements, thereby facilitating the synthesis of novel materials with tailored properties. This study explored Ce3+-doped Tb3Al5−xScxO12 crystals (where x ranges from 0.5 to 3.0), revealing a novel approach to control luminescence and photoconversion through atomic size mismatch engineering. Raman spectroscopy confirmed the coexistence of garnet and perovskite phases, with Sc substitution significantly influencing the garnet lattice and induced A1g mode softening up to Sc concentration x = 2.0. The Sc atoms controlled sub-eutectic inclusion formation, creating efficient light scattering centers and unveiling a compositional threshold for octahedral site saturation. This modulation enabled the control of energy transfer dynamics between Ce3+ and Tb3+ ions, enhancing luminescence and mitigating quenching. The Sc admixing process regulated luminous efficacy (LE), color rendering index (CRI), and correlated color temperature (CCT), with adjustments in CRI from 68 to 84 and CCT from 3545 K to 12,958 K. The Ce3+-doped Tb3Al5−xScxO12 crystal (where x = 2.0) achieved the highest LE of 114.6 lm/W and emitted light at a CCT of 4942 K, similar to daylight white. This approach enables the design and development of functional materials with tailored optical properties applicable to lighting technology, persistent phosphors, scintillators, and storage phosphors

Lead-free piezoelectric crystals grown by the micro-pulling down technique in the BaTiO3–CaTiO3–BaZrO3 system

BaTiO3-based crystal fibres with mm-sized grains were grown by the micro-pulling down technique from the BaTiO3–CaTiO3–BaZrO3 solid solution with pulling velocities of about 6, 9 and 15 mm h−1. The natural growth direction was identified as (001)pc. For the pulling velocities of about 15 mm h−1 and 9 mm h−1, effective partition coefficients have been calculated from Castaing micro-probe measurements, and gave, respectively, 1.3 and 2 for Zr, and 0.95 and 0.9 for Ca. Laser-induced breakdown spectroscopy measurements reveal a strong inhomogeneity and variations of Zr contents while Ca contents show an opposite variation trend with a more steady distribution. Coexistence of two crystallized perovskite solid solutions is suggested. Most efficient polycrystals with mm-sized grains and 0.5 mol% Zr and 11 mol% Ca as average contents exhibit Curie temperatures higher than 113 °C, electromechanical coupling factors kt up to 41% and piezoelectric charge coefficients d33 up to 242 pC N−1 at room temperature. These values are similar to piezoelectric coefficients reported in the literature for oriented flux-grown single crystals with close compositions. Both chemical and physical results obtained in the BCTZ system make the μ-PD technique a promising way to improve the piezoelectric response of lead-free solid solution-based single crystals

Charge trapping and luminescence of the mixed size CsPbBr3 particles grown in one batch

Cesium lead bromide (CsPbBr3, CPB) powder formed by micro-, nanocrystals (MC, NC) and quantum dots (QD) was synthesized as free-standing and polystyrene covered. Luminescence was multicomponent, in general, ranging from below 1.9 eV up to about 2.6 eV. The ultrafast decay kinetics exhibited strong decay time component with the value of 260 ps. Electron paramagnetic resonance (EPR) revealed surface defects like O2 and some spin transitions most likely originating from some complex defect, supposedly F-Vk(H) dimer center under the constant ultraviolet (UV) light irradiation at the temperature T =10 K. The thermal release of the electrons from the O2 center was correlated with the 117 K thermally stimulated luminescence (TSL) peak. Coating with polystyrene resulted in the about doubly increased decay time of luminescence. The O2 and F-Vk(H) EPR resonances were not observed as well. The TSL peak which might be ascribed to the O2 was not clearly detected anymore. The glow curve was composed of one very broad peak typical for the amorphous materials. At the same time, the polystyrene prevented the MCs creation. The existence of charge/energy transfer between the CPB and polystyrene due to the chemical bonding was assumed and confirmed also by calculations