Light-emitting diodes (LEDs) based on metal halide perovskite quantum dots (QDs) have achieved impressive external quantum efficiencies; however, the lack of surface protection of QDs, combined with efficiency droop, decreases device operating lifetime at brightnesses of interest. The epitaxial incorporation of QDs within a semiconducting shell provides surface passivation and exciton confinement. Achieving this goal in the case of perovskite QDs remains an unsolved challenge in view of the materials' chemical instability. Here, we report perovskite QDs that remain stable in a thin layer of precursor solution of perovskite, and we use strained QDs as nucleation centers to drive the homogeneous crystallization of a perovskite matrix. Type-I band alignment ensures that the QDs are charge acceptors and radiative emitters. The new materials show suppressed Auger bi-excition recombination and bright luminescence at high excitation (600 W cm-2), whereas control materials exhibit severe bleaching. Primary red LEDs based on the new materials show an external quantum efficiency of 18%, and these retain high performance to brightnesses exceeding 4700 cd m-2. The new materials enable LEDs having an operating half-life of 2400 h at an initial luminance of 100 cd m-2, representing a 100-fold enhancement relative to the best primary red perovskite LEDs.