The optical properties of digital-alloy InGaAlAs grown with (In0.(53)Ga0.As-47) n/(In-0.Al-52(0).As-48) n short-period superlattices by molecular beam epitaxy as a function of the period length n, n = 1, 2, 4, 5 monolayers (MLs), have been investigated by using excitation-laser power (I-exc)-dependent photoluminescence (PL) and emission-photon energy-dependent time-resolved PL at 10 K. With increasing n from 1 to 5 MLs, the redshift of the PL peak, the increase of the PL intensity, and the decrease of the full width at half maximum of the PL peak are observed, and these results are interpreted as the reduced quantized energy and enhancedwave function overlap due to the increased well width, and decreased alloy scattering due to the potential fluctuations. As n increases from 1 to 5 MLs, the blueshift of the PL peak (exciton transition) with increasing Iexc is reduced and the PL decay of the exciton emission peak also becomes faster, and these results are attributed to smaller potential fluctuations with increasing n. It is shown that the emission energy and luminescence properties of digital-alloy InGaAlAs are dependent on the period length n (well and barrier widths). (C) 2017 Elsevier B.V. All rights reserved.