Optical properties of digital-alloy InGaAlP and InGaP/InGaAlP multiple-quantum wells (MQWs) grown by molecular beam epitaxy were characterized by 300 and 10K-photoluminescence (PL). For digital-alloy In-0.49 (Ga1-zAlz)(0.51)P grown at 425 degrees C with z = 0.2, 0.4, and 0.5, the energies of PL peak were in the range 2.0-2.167 eV. As the growth temperature increased from 425 to 470 degrees C for the digital-alloy In-0.49(Ga0.6Al0.4)(0.51)P, the intensity of PL peak increased 2.5 times. However, the energy and line width of PL spectrum did not change significantly. The L peak at 2.148 eV and the H peak at 2.189 eV from 8 K-PL were also observed and the intensity ratios of L peak to H peak I-L/ I-H) were 0.046, 0.048, and 0.043 for 425, 450, and 475 degrees C, respectively. For the digital-alloy InGaP/InGaAlP MQW structure grown at 450 degrees C PL peak energy of 1.911 eV and PL line width of 38 meV were obtained successfully. The band gap and compositions of InGaAlP were easily controlled by digital-alloy technique without degrading the crystal quality. (c) 2005 Elsevier B.V. All rights reserved.