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Abstract
The optical spectra (200-20000 cm−1) of A2MCl4 + of A2MCl4 (A=NH4 +, N(CH3)4 +, NH(CH3)3 +, NH2(CH3)2 +, N(C2H5)4 +, NH2(C2H5)2 +, NH3(C2H5)+N(CH3)4 +; M=Cu, Co) ferroelectric crystals with organic cations at different temperatures have been investigated. Using Gaussian analysis and Tanabe-Sugano diagram, the absorption maximum positions and the electron transitions have been determined. The experimental results have been discussed based upon theory of the crystalline field. It means, that the structural phase transitions exist in the material. In some of these crystals the thermochromic effects as results of structural phase transitions have been observed. The phenomenon of phase transition in [NH2(C2H5)2]2CuCl4 with change of colour from green to yellow can be used for production of ultraviolet detectors.