Effect of alkaline earth and transition metals doping on the properties and crystalline perfection of potassium hydrogen phthalate (KHP) crystals

The influence of alkaline earth metal (Mg) and transition metal (Hg) doping on the properties and crystalline perfection of potassium hydrogen phthalate (KHP) crystals has been described. Incorporation of dopant into the crystalline matrix even at the low concentrations was well confirmed by energy dispersive X-ray spectroscopy (EDS). Further, high-resolution X-ray diffraction (HRXRD) studies indicate predominant substitutional site occupancy for Mg. Heavy doping results in internal structural grain boundaries due to stress aroused in the lattice caused by the entry of dopants into the crystalline matrix. The transition metal (Hg) doping results in multi-peaks in the diffraction curve (DC) with a wide angular spread and the site occupancy seems to be predominantly interstitial positions in the crystal lattice, quite likely due to its bigger size in comparison with alkaline earth metal. The reduction in the intensity observed in powder X-ray diffraction (XRD) for both types of doped specimens and slight shifts in vibrational frequencies reveal minor structural variations. It is observed that the doping with high concentrations of metal facilitates nonlinearity and enhances the second harmonic generation (SHG) efficiency to a significant extent.