Stable and efficient red phosphorescent materials are insistently demanded for their importance in OLED applications. In this article, we report the syntheses, characterization, and photophysical properties of three binuclear platinum(II) complexes Pt₂(Stpip)₂L(1–3) and their three corresponding mononuclear complexes Pt(Stpip)L(1–3)H (Stpip = bis(diphenylphorothioyl)amide; L1H₂ = 2,5-bis(3-methylphenyl)pyrazine; L2H₂ = 2,5-bis([1,1′-biphenyl]-3-yl)pyrazine; L3H₂ = 1,4-diazanaphthalene). All of the six complexes were characterized by single-crystal X-ray diffraction except complex Pt₂(Stpip)₂L1. Moreover, three binuclear complexes Pt₂(Stpip)₂L(1–3) exhibit intense phosphorescence at 594 nm, 609 nm, and 660 nm in degassed CH₂Cl₂ at room temperature (r.t.), respectively. However, three mononuclear complexes Pt(Stpip)L(1–3)H are non-emissive in degassed CH₂Cl₂ at r.t. Among these three binuclear complexes, Pt₂(Stpip)₂L3 exhibits red emission at 640 nm with a quantum efficiency of 49% and a lifetime of 2.94 μs for a 12 wt% PYD2 film while the mononuclear Pt(Stpip)L3H exhibits phosphorescence at 562 nm with a quantum efficiency of 88% and a lifetime of 2.97 μs for the 12 wt% PYD2 film. Furthermore, two light-emitting devices utilizing Pt₂(Stpip)₂L3 and Pt(Stpip)L3H as triplet emitters were fabricated using a solution process and these two devices exhibited maximum external quantum efficiencies of 7.72% with CIE coordinates of (0.68, 0.31) and 15.78% with CIE coordinates of (0.46, 0.53), respectively.