Synthesis and Eu3+ luminescence in new oxysilicates, ALa3Bi(SiO4)3O and ALa2Bi2(SiO4)3O [ACa, Sr and Ba] with apatite-related structure

Site preference and local structural stability of Bi(III) substitution in hydroxyapatite using first-principles simulations

Bismuth (Bi(III)) substitution in hydroxyapatite (HAp) lattice confers unique properties such as antibacterial, catalytic, radiosensitization, and conductive properties while preserving the innate bioactivity. Understanding the local structural changes upon Bi3+ substitution is essential for controlling the stability and optimizing the properties of HAp. Despite numerous experimental studies, the precise substitution behaviors, such as site preference and structural stability, remain incompletely understood. In this study, the substitution behavior of Bi(III) into the HAp lattice with formula of Ca9Bi(PO4)6(O)(OH) was investigated via first-principles simulation by implementing density functional theory. Energy calculations showed that Bi3+ preferentially occupies the Ca(2) site with an energy difference of ∼0.02 eV per atom. Local structure analysis revealed higher bond population values and an oxygen coordination shift from 7 to 6 for the Ca(2) site, attributed to the greater covalent interactions and its flexible environment accommodating the bulky Bi3+ ion and its stereochemically active lone pair. This work provides the first comprehensive investigation on Bi3+ ion substitution site preference in HAp using first-principles simulations.

Second-Sphere Polyhedron-Distortion-Induced Broadened and Red-Shifted Emission in Lu3(MgxAl2-x)(Al3-xSix)O12:Ce3+ for Warm WLED

Orange-yellow phosphors with extended broadband emission are highly desirable for warmer white-light-emitting diodes (WLED) with a higher color-rendering index. Targeted phosphors Ce³⁺-doped Lu₃(Mg_xAl_2-x)(Al_3-xSi_x)O₁₂ (x = 0, 0.25, 0.50, 0.75, and 1.00) were developed by chemical composition modification for luminescent tuning from green to orange-yellow with spectral broadening. The correlation between structure evolution and luminescent properties was elucidated by the local structure, fluorescence lifetime, and Eu³⁺ luminescence as a structural probe. The polyhedron distortion in the second-sphere coordination leads to the site differentiation and symmetry degradation of Ce³⁺ with the accommodation of (MgSi)⁶⁺ pairs, comprehensively resulting in the red shift (540 → 564 nm) and broadening in emission spectra. The WLED fabrication results demonstrate that the red shift and broadening in the emission of Lu₃(Mg_xAl_2-x)(Al_3-xSi_x)O₁₂:Ce³⁺ make it more suitable for the single-phosphor converted warm WLED.

Crystal Chemical Substitution at Ca and La Sites in CaLa4(SiO4)3O To Design the Composition Ca1- xM xLa4-xRE x(SiO4)3O for Nuclear Waste Immobilization and Its Influence on the Thermal Expansion Behavior

The oxysilicate apatite host CaLa₄(SiO₄)₃O has been explored for immobilization of radioactive nuclides. Divalent ion, trivalent rare earth ion, and combined ionic substitutions in the silicate oxyapatite were carried out to optimize the simulated wasteform composition. The phases were characterized by powder X-ray diffraction, FT-IR, TGA, SEM-EDS, and HT-XRD techniques. The results revealed the effect of ionic substitutions on the structure and thermal expansion behavior. The investigation resulted in the formulation of simulated wasteforms such as La_3.4Ce_0.1Pr_0.1Nd_0.1Sm_0.1Gd_0.1Y_0.1(SiO₄)₃O (WF-1) and Ca_0.8Sr_0.1Pb_0.1La_3.4Ce_0.1Pr_0.1Nd_0.1Sm_0.1Gd_0.1Y_0.1(SiO₄)₃O (WF-2). In comparison to the average axial thermal expansion coefficients of the hexagonal unit cell of the parent CaLa₄(SiO₄)₃O measured in the temperature range 298-1073 K (α' _a = 9.74 × 10^-6 K^-1 and α' _c = 10.10 × 10^-6 K^-1), rare earth ion substitution decreases the thermal expansion coefficients, as in the case of La_3.4Ce_0.1Pr_0.1Nd_0.1Sm_0.1Gd_0.1Y_0.1(SiO₄)₃O (α' _a = 8.67 × 10^-6 K^-1 and α' _c = 7.94 × 10^-6 K^-1). However, the phase Ca_0.8Sr_0.1Pb_0.1La_3.4Ce_0.1Pr_0.1Nd_0.1Sm_0.1Gd_0.1Y_0.1(SiO₄)₃O shows an increase in the values of thermal expansion coefficients: α' _a = 11.74 × 10^-6 K^-1 and α' _c = 11.70 × 10^-6 K^-1.

Excitation-dependent local symmetry reversal in single host lattice Ba2A(BO3)2:Eu3+ [A = Mg and Ca] phosphors with tunable emission colours

Excitation-dependent emission colour tuning in single host lattice phosphors by local symmetry changes due to reorganization of highly strained oxygen.