[en] We briefly review our recent results of the strain effects on photoluminescence (PL) properties of Er in tensile strained Si on a SiGe layer (Si:Er:O/SiGe) and compressively strained SiGe on a Si layer (SiGe:Er:O/Si) grown by molecular beam epitaxy, and present new results of electroluminescence (EL) properties of Er in homo- and hetero-epitaxially grown p-i-n diodes (p-Si/i-Si:Er:O/n-Si, p-SiGe/i-SiGe:Er:O/n-Si), where we grew an intrinsic Si or SiGe layer doped with Er and oxygen on an n-type Si substrate and subsequently grew a p-type Si or SiGe top layer. We observed Er-related PL around 1.54 μm at 77 K in both tensile and compressively strained samples. The PL intensity of these strained samples was much stronger than that of unstrained (Si:Er:O/Si) samples. Moreover, we still observed intensive PL in strained samples even with low Er concentrations far below 10¹⁸ cm^-3, at which unstrained samples showed only weak or no luminescence. Such enhancing effects strongly suggest that the probability of Er optical transition can be enhanced by the presence of both tensile and compressive strains. We also observed Er-related PL and EL around 1.54 μm at 77 K in the p-i-n diodes, and found that annealing at 800 deg. C increased both of PL and EL intensities