Fluorescence and laser properties of Nd-doped (Ca _0.5 Sr _0.5 ) ₁₀ (PO ₄ ) ₆ F ₂ ceramics

Transparent ceramics of Nd 3+ -doped (Ca 0.5 Sr 0.5 ) 10 (PO 4 ) 6 F 2 (CS-FAP), a solid solution of hexagonal fluorapatite Ca 10 (PO 4 ) 6 F 2 (C-FAP) and Sr 10 (PO 4 ) 6 F 2 (S-FAP), was successfully fabricated. Laser oscillation from Nd:CS-FAP was demonstrated for the first time. The ceramics consisted of fine grains with an average grain size of approximately 100 nm. Despite a non-cubic crystal structure, light scattering due to birefringence was small, and the total loss coefficient near 1 μm was approximately 0.5 cm −1 . The full width at half maximum (FWHM) of the fluorescence spectra was about 3.5 nm (31 cm −1 ) at 1 μm and 6.4 nm (36 cm −1 ) at 1.3 μm, respectively. They were substantially broader than those of C-FAP and S-FAP (both approximately 1 nm), resulting from lattice distortion due to solid solution formation. The fluorescence peak wavelengths and laser oscillation wavelengths (1061 nm and 1333 nm) were intermediate between those of C-FAP and S-FAP. The Ca to Sr ratio can be controlled, providing compositional design flexibility and the potential of CS-FAP ceramics as novel ultrashort-pulse laser materials.