Influence of an alkali metal dopant Rb on the structural, mechanical and optical properties of an UV-transparent ammonium pentaborate crystal.

The UV transparent nonlinear optical crystals of undoped and Rb doped ammonium pentaborate tetrahydrate have been grown by slow evaporation technique at 32 °C. Presence of dopants in the crystal lattice is confirmed by energy dispersive X-ray analysis and by the reduced intensity of NH stretching vibrations in the Raman spectrum. Enlargement of the unit cell of Rb doped crystal is in correlation with the size of the dopant. The symmetry in rocking curve of the high resolution X-ray diffraction analysis reveals that the dopants occupied the substitutional positions in the host crystal. Both the grown crystals exhibit wide transparency from 230 nm to 900 nm and thermally stable up to 130 °C. Significant improvement is observed in the microhardness of Rb doped crystal. Rb doped crystal exhibit a better response to the laser interactions in terms of enhanced second harmonic generation efficiency, increment in third-order susceptibility and laser damage threshold values. The third-order susceptibility and laser damage threshold values of Rb doped crystal are 5.442 × 10 esu and 16.92 GW/cm respectively.