Optical and mechanical stability of Tutton’s salt crystal of Cu doped ammonium cobalt(II) sulfate hexahydrate

Cu doped ammonium cobalt(II) sulfate hexahydrate (ACSH) crystals were investigated for LED applications. Cu doped ACSH crystals obtained via slow evaporation technique were analyzed for their structural, morphological, optical, thermal, and mechanical properties. The compound formed a crystalline structure within the monoclinic system (P2). FTIR and Raman spectral analyses ascertained peaks pertaining to ν(O–H), and ν(N–H) corresponding to NH and M–HO groups. The presence of N, O, S, Co, and Cu was demonstrated through EDAX. The peaks at 450 and 530 nm are ascribed to the [Co(HO)] center due to T → T(P) and T → A transitions. The photoluminescence spectrum showed a red emission at 778 nm on excitation at 520 nm. The EPR spectrum indicated a strong tetragonal distortion in [Cu(HO)], and the crystal is comprised of a H-bonded structure involving [Co(HO)], [Cu(HO)], NH, and SO networks. The TG–DTA–DSC study showed the loss of water molecules and the subsequent decomposition of the compound. The material exhibited a reverse indentation size effect (n = 3.9) according to Kick's law. The mechanical properties, such as microhardness, yield strength, stiffness constant, fracture toughness, and brittleness of the crystal were calculated. The laser-induced damage threshold of the ACSH crystal doped with Cu was determined to be 29.89 GW/cm, which is superior to those of urea or KDP crystals. The results support that the developed crystal can be effectively employed in light-emitting diode applications.