Stranski-Krastanov growth in molecular beam epitaxy allows the preparation of self assembling InAs and InP quantum dots on GaAs and Ga0.52In0.48P buffer layers, respectively. InAs dots in GaAs prepared by slow growth rates and low temperature overgrowth provide intense photoluminescence at the technologically important wavelength of 1.3 mum at room temperature. Strain induced vertical alignment, size modification and material interdiffusion for stacked dot layers are studied. A blue shift of the ground state transition energy is observed for the slowly deposited stacked InAs dots. This is ascribed to enhanced strain driven intermixing in vertically aligned islands. For very small densely stacked InP and InAs dots the reduced confinement shift causes a red shift of the ground state emission. The InP quantum dots show intense and narrow photoluminescence at room temperature in the visible red spectral range. First InP/Ga0.52In0.48P quantum dot injection lasers are prepared using threefold stacked InP dots. We observe lasing at room temperature in the wavelength range between 690-705 nm depending on the size of the stacked InP dots.