We report, herein, the use of phosphorescent copper(I)–silver(I) heterometallic complexes to achieve highly efficient electroluminescence. The trigonal prism arranged Ag₆Cu heteroheptanuclear alkynyl cluster complexes show intense phosphorescence in a fluid solution, powder and thin film with quantum yields as high as 0.78. Complex 1 with 1-(tert-butyl)-4-ethynylbenzene (HCCC₆H₄Bu^t-4) shows reversible phosphorescence vaporchromism in respose to THF or CHCl₃. The phosphorescent emission exhibits an obvious blue-shift from 580 nm to 530 nm for THF and to 538 nm for CHCl₃ with a remarkable luminescence change from bright yellow to green. As demonstrated experimentally and theoretically, the phosphorescence originates from ³[π(aromatic acetylide) → s/p(Ag₆Cu)]³LMCT and Ag₆Cu cluster centered ³[d → s/p] triplet states. Taking advantage of the doped light-emitting layer of 57% TCTA:28% OXD-7:15% Ag₆Cu complex with hole-transporting TCTA and electron-transporting OXD-7 as a blended host, solution-processed OLEDs gave highly efficient electroluminescence with a current efficiency (CE) of 42.5 cd A⁻¹ and external quantum efficiency (EQE) of 13.9% at low voltage (4.5 V) with a practical brightness of 184 cd m⁻².