The first observation of luminescence from Ag(i) complexes with a square-planar geometry of the metal is reported. [Ag(Py ₃PO) ₂]ClO ₄ and [Ag(Py ₃PO) ₂]OTf-first examples of the emissive square-planar Ag(i) complexes-have been synthesized by the reaction of tris(2-pyridyl)phosphine oxide (Py ₃PO) with Ag(i) salts. Both complexes exhibit pronounced photoluminescence in the solid state at ambient temperature with nano- and microsecond lifetime components. Remarkably, the luminescence of the complexes has a reversible thermochromic behavior, changing their emission color from yellow (λemmax ≈ 585 nm) at room temperature to red-orange (λemmax = 620 nm) at 77 K. The spectroscopic and computational results reveal that the emission of the title compounds can be assigned to the ³MLCT phosphorescence with admixture of the ¹MLCT fluorescence.