The electronic transition energies of the Mx[Pt²⁺(CN)₄]•mH₂O compounds, crystallizing in columnar structures, depend strongly on the Pt-Pt distance R in the direction of the columns. R can be varied by substituting M and/or by application of high pressure. Using three different compounds {Na₂[Pt(CN)₄]•3H₂O, Ca[Pt(CN)₄]•5H₂O, Mg[Pt(CN)₄]•7H₂O} and applying hydrostatic pressures up to 38 kbar it is possible to adjust the emission energy continously from 3.3 to about 1.35 eV. The pressure-induced energy shift is unusually large with values between -320 and -140 cm⁻¹/kbar.