Single-Crystal Terbium Silicate Chloride Core–Shell Nanowires and Nanotubes for Monolithically Integrated Optoelectronics

The density of doped rare-earth (RE) ions in most host materials is often too low to support sufficient optical gain for monolithically integrated optoelectronics, limited by the inevitable precipitation of RE ions at high density. This challenge can potentially be overcome with RE-containing single crystals. In this work, a monocrystalline terbium silicate chloride in the form of core–shell and tubular nanostructures is synthesized by one-step chemical vapor deposition. The Rietveld refinement analysis of X-ray diffraction shows that this single crystal has the formula Tb3(SiO4)2Cl and belongs to the orthorhombic Pnma space group with unit cell parameters a = 6.858 Å, b = 17.737 Å, c = 6.179 Å, and α = β = γ = 90° and a unit cell volume 7.54 nm3. To the best of our knowledge, single-crystal Tb3(SiO4)2Cl is a RE silicate that has never been reported before. Compared to Tb-doped materials, Tb3(SiO4)2Cl has the advantages of single crystal, higher Tb3+ density (1.6 × 1022 cm–3), and chemical/thermal stability (950 °C). Upon illumination, Tb3(SiO4)2Cl emits a strong characteristic green light with crystal-field-induced splitting and no concentration- and temperature-induced quenching. The conversion from core–shell nanowires to nanotubes is interpreted by the synergistic influence of surface chemical reactions and lateral atomic diffusion driven by the Kirkendall effect. Given the high terbium density and thermal stability of these nanostructures and the chemical involvement of silicon during their formation, they are promising candidates for the implementation of compact Si-compatible green light (e.g., giant optical gain, low-threshold waveguide amplifiers, and monolithic lasers) desirable for next-generation monolithically integrated optoelectronics.