Origin of periodic domain structure in Er3+-doped β′-(Sm,Gd)2(MoO4)3 crystal lines patterned by laser irradiations in glasses

Er3+-doped β′-(Sm,Gd)2(MoO4)3 crystal lines are patterned on the surface of Er2O3–Gd2O3–Sm2O3–MoO3–B2O3 glasses by continuous-wave Yb:YVO4 laser irradiations (wavelength: 1080 nm, power: 1.3 W, scanning speeds: 5 μm/s), and the origin of the periodicity of self-organized domain structures with high and low refractive index regions in crystal lines is examined from polarized optical microscope (POM) observations, micro-Raman scattering spectrum, and photoluminescence spectrum measurements. It is found that the periodicity of domain structures changes largely depending on Er2O3 content, i.e., the length of high (bright color in POM observations) and low (dark color) refractive index regions increases with increasing Er2O3 content and homogeneous crystal lines with no periodic domain structures are patterned in Er2O3–Sm2O3–MoO3–B2O3 glass with no Gd2O3. Considering that the degree of ferroelasticities in β′-(Sm,Gd)2(MoO4)3 crystals decreases due to the incorporation of Er3+ ions, it is demonstrated that the origin of periodic domain structures in laser-patterned lines is due to spontaneous strains in ferroelastic β′-(Sm,Gd)2(MoO4)3 crystals.