Effect of chemical etching on the surface morphology of laser-patterned lines with Er3+-doped CaF2 nanocrystals in oxyfluoride glass

The chemical etching behavior for the lines consisting of Er3+-doped CaF2 nanocrystals patterned on the surface of an oxyfluoride glass by using a laser-induced crystallization technique (laser: Yb-doped YVO4; wavelength: 1080 nm; power: 1.7 W; a scanning speed: 2 μm/s) in a nitric acid solution (1N HNO3) is examined, and the morphology change in the lines due to the etching is characterized from confocal laser microscope observations and photoluminescence (PL) spectrum measurements of Er3+ ions. The higher and wider bumps compared with the bump of the original line (no etching) are observed in etched lines, and in particular, the surrounding of lines is etching away preferentially, forming the groove in both sides of line. PL spectra of Er3+ ions with strong intensities are observed from etched lines, suggesting that Er3+-doped CaF2 nanocrystals are largely present just at the surface of etched lines. It is found that the chemical etching rate (1.2 × 10−2 μm/min) of the crystallized bulk sample is smaller than that (5.4 × 10−2 μm/min) of the precursor bulk glass, suggesting that CaF2 nanocrystals formed have a high resistance against the chemical attack.