Effect of l-threonine on growth and properties of ammonium dihydrogen phosphate crystal

Ammonium dihydrogen phosphate (ADP) is an important nonlinear optical (NLO) material used for electro-optical applications and finds various NLO applications using Nd:YAG and Nd:YLF Lasers. The Amino acids have properties like molecular chirality and zwitter ionic nature helps to improve NLO properties of ADP. The pure and l-threonine doped ADP crystals are grown using slow solvent evaporation technique at room temperature. The Powder XRD spectra suggest tetragonal crystal system and slight shifting of peak. The FT-IR spectra verify the presence of various functional groups of pure and doped ADP crystals. The FT-Raman shows strong absorption peak at 922 cm−1 due to asymmetric stretching of PO43− for all samples without shifting indicating the single phase nature of all samples. The photoluminescence study suggests the presence of defects in doped samples compared to the pure one due to increase of Stokes shift and vibrational energy relaxation phenomena. The presences of constituent elements are indentified using CHN analysis. The optical transmittance, energy band gap, skin depth, refractive index and extinction coefficient is study using UV–Visible spectroscopy and the dispersive behaviour of refractive index below absorption edge is study using Wemple-DiDomenico single oscillator model. The variation of capacitance and conductance is study using complex admittance spectroscopy. All the grown crystals have possessed negative photoconductivity. The second and third harmonic generation efficiency is increased nearly to double for l-threonine doped ADP crystals compared to pure Potassium dihydrogen phosphate (KDP). The laser damage threshold is measure for pure and doped ADP crystals. Keywords: ADP, Vibrational energy relaxation, Stoke shift, Wemple-DiDomenico single oscillator model, Z-scan, Complex admittance