Characterization of a potential nonlinear optical material: Sodium fluoride additive on ammonium dihydrogen orthophosphate single crystals

Effects of the additions of sodium fluoride (NaF) on the growth, structural and various optical properties of ammonium dihydrogen orthophosphate (ADP) single crystals grown by a slow evaporation solution growth technique from aqueous solution has been investigated. Crystallinity of the grown crystals was studied by powder X-ray diffraction analysis. Both pure and NaF doped ADP crystals exhibit tetragonal crystal structure. UV–vis–NIR spectral analysis was carried out to study the optical characteristics of the crystals which reveal that the cutoff wavelength for both pure and NaF doped ADP crystal is around 300 nm. From the spectra it can be clearly inferred that the transmittance percentage is increased in the NaF doped crystals. Also there is an absence of characteristic absorption in the region between 340 and 1200 nm, which is a most desirable property of a material for both SHG and other NLO applications. The bonding structure and molecular associations due to chemical reactions were analyzed by FTIR analysis. It also confirms the functional groups present in the grown crystals. Second harmonic generation (SHG) test adopting Kurtz-Perry technique revealed that the second harmonic generation efficiency of NaF doped ADP is 1.3 times that of pure ADP crystal.