Germanium wafers have been modified by a technique of laser-induced air breakdown processing. It has been found that the treatment leads to the formation of porous layers, containing nanoscale holes, and consists of Ge nanocrystals embedded into GeO2 matrices. They exhibit strong and stable photoluminescence in the green and UV ranges (2.2 and 2.9 eV), whose appearance could be explained by defects in the GeO2 matrix or quantum confinement effects. The locally patterned layers are of importance for optoelectronics and biosensing applications. [ABSTRACT FROM AUTHOR]