The aim of this study is to explain the properties of unusual photoluminescence spectrum of nanohills formed on a surface of Si crystal by laser radiation. Si is an elementary semiconductor with indirected band structure. Therefore, quantum efficiency of photoluminescence (PL) is very low and usually maximum of spectrum is situated at 1.12 eV. Several scientific groups have shown the possibility of shift of Si and Ge radiative IR-spectrum in visible region of spectrum using Si and Ge nanoparticles implanted into SiO2 layer. This phenomenon is explained by Quantum Confinement Effect (QCE) in nanodots. Investigation of interaction of powerful laser radiation with Si and Ge single crystals was carried out in order to show the possibility of nanohills formation on irradiated surface, Wide PL spectrum of nanodots and nanohills was explained by size-wise non-homogeneous distribution of nanoparticles. PL spectra of SiGVSi and Si structures irradiated by Nd:YAG laser second harmonics at intensity of up to 2.0 MW/cm2 and non-irradiated structure have been studded experimentally. PL spectrum of the irradiated structure is asymmetric with maximum at 2.0 eV and has a long shoulder in the red region of spectrum. Investigation of the irradiated Si surface morphology has shown formation of nanohills of "pin acacia"-like shape which led us to conclude that such properties of PL is connected with the shape of nanohills. Investigation of three shapes of nanohills' surface, i.e., square parabola rotation around symmetry axis ("dome"), triangle ("cone") and reverse parabola (''pin acacia") has shown that at the same height and base of the figures, in the last two structures QCE takes place because the relation d < RB for the presence of QCE (Bohrs’ radius for electron and hole must be bigger than the diameter of nanostructure) fulfill and it does not fulfill for Che first case. As a result PL spectrum for the three figures will be different: for the first shape it will be the same as tor the bulk semiconductor, for the second one — it will be Gaussian with "blue shift" in comparison with the previous spectrum, for the third one - wide spectrum with "blue shift" in comparison with the previous one. The last statement is confirmed by our calculation of band-gap in nanohill-nanowires with gradually change of diameter from substrate till top of nanohill. The calculation has shown the presence of graded band-gap structure with maximum of band-gap value on the top of nanohills.