Photoluminescence and transformation of dense Al2O3:Cr3+ condensates synthesized by laser-ablation route

Dense Al2O3 condensates doped with ca. 1 at% Cr3+ in the γ- and α-forms were synthesized by energetic Nd-YAG pulse laser ablation on clamped Al/Cr targets in oxygen. The analytical electron microscopic observations indicated the γ-form was up to an abnormal large size of 2 μm and the α-form several times larger in size. The two forms were under residual compressive stress up to several GPa according to room-temperature lattice parameters. Such a residual stress level was also indicated by the red shift of photoluminescence R1 and R2 lines for the as-formed α-condensates and the secondary α-phase due to γ–δ–θ–α transformation upon 400 nm excitation at 2 mJ/pulse. The Al2O3:Cr3+ condensates are potential luminescence sensors of phase change and residual stress for industrial applications and may shed light on natural dynamic settings.