Effect of Sr²⁺ on growth and properties of ammonium dihydrogen phosphate single crystal

The ammonium dihydrogen phosphate (ADP) crystals have wide range of non-linear optical applications. The doping of bivalent impurity like strontium can strongly retard growth rate and modify properties of ADP crystals. The pure and 0.5 mol% Sr²⁺ doped ADP crystals are grown by using the slow evaporation technique at room temperature. The powder XRD indicates the single phase nature of both samples. The FT-IR spectra indicate the shifting of absorption peaks for the doped sample. The thermal study indicates that the doped sample is thermally less stable than the pure sample. The EDAX study confirms the presence of strontium in the doped sample. The UV–Vis spectra indicate slight decrement in the transmittance due Sr²⁺ doping. The Wemple–DiDomenico model is satisfactorily applied to dispersive behaviour of refractive index. The dielectric constant and dielectric loss decreases with frequency increased. The Jonscher’s power law is studied for A.C. conductivity. The Nyquist plot and complex modulus plot exhibits two semicircles for pure ADP due to grain and grain boundary contributions and the same plots show single semicircle for doped ADP due to grain contribution only. The stretch exponent (β) is obtained less than unity, indicates the non-Debye type relaxation process. The second harmonic generation efficiency of fundamental laser beam is found to be 2.07 and 1.54 times higher than the pure KDP for pure ADP and Sr²⁺ doped ADP, respectively. The Z-scan study reveals the self focusing and reverses saturable absorption kind of nonlinear response for both samples.