Efficient vacuum-processed organic light-emitting diodes are fabricated using a carbene-metal-amide material, CMA1. An electroluminescence (EL) external quantum efficiency of 23% is achieved in a host-free emissive layer comprising pure CMA1. Furthermore external quantum efficiencies of up to 26.9% are achieved in host-guest emissive layers. EL spectra are found to depend on both the emissive-layer doping concentration and the choice of host material, enabling tuning of emission color from mid-green (Commission Internationale de l'Éclairage co-ordinates [0.24, 0.46]) to sky blue ([0.22 0.35]) without changing dopant. This tuning is achieved without compromising luminescence efficiency (>80%) while maintaining a short radiative lifetime of triplets (<1 μs).