@article{PismaZhETF.58.197,
    title = {Observation of 2D-exciton luminescence in germanium layers in periodic $Ge-Ge_{1-x}Si_x$ heterostructures},
    author = {Kalugin, N. G. and Orlov, L. K. and Kuznetsov, O. A.},
    journal = {πΙΣΨΝΑ Χ φότζ},
    volume = {58},
    issue = {3},
    pages = {197},
    year = {1993},
    doi = {},
    url = {http://jetpletters.ru/ps/0/article_17901.shtml},
}