Optical studies on electron beam evaporated lithium triborate films

Lithium triborate (LB3) has numerous applications in scintillator for neutron detection, laser weapon and communication. LB3 films have been prepared by electron beam evaporation technique under a pressure of 1×10(-5) mbar on glass substrate at 323 K for 4 min. The crystallographic orientations and the lattice parameters (a=8.55 (2); b=5.09 (2); c=7.39 (2)Å) were determined by powder XRD indicating the (111) preferential orientation of the film. The lower cut off wavelength at 325 nm with 75% transparency was measured from the UV-vis spectrum. The optical constants extinction coefficient (K), reflectance (R), the linear refractive index (1.34) and the optical energy band gap (~4.0 eV) were estimated. The photoluminescence spectrum shows the emission peak in the visible region with low concentration of oxygen defects. LB3 is found to be second harmonic generation (SHG) active using a Q-switched Nd:YAG laser (1064 nm, 9 ns, 10 Hz). The nonlinear refractive index (n(2)~10(-16) cm(2)/W) and nonlinear absorption coefficient (β~10(-2) cm/W) reveal (Z-scan technique) that the material has negative nonlinearity and self-focusing nature.