Temperature-dependent photoluminescence (PL) studies of Ge1-ySny (y=4.3%-9.0%) alloys grown on Ge-buffered Si substrates by using a chemical vapor deposition have been performed as a function of Sn content. The PL results of Ge1-ySny alloys with high Sn content (≥ 7.0%) exhibit typical characteristics of direct bandgap semiconductors, such as an increase of PL intensity with decreasing temperature and a single PL emission peak from the direct bandgap (Γ-valley) to the valence band at all temperatures from 10 to 300 K. While for Ge1-ySny alloys with low Sn content (≤ 6.2%), both the direct bandgap (ED) and the indirect bandgap (EID) PL emission peaks are appeared at most temperatures and as temperature increases, the integrated PL intensities of ED initially increase and then decrease, and they finally increase again. However, the integrated PL intensities of EID peaks show different temperature-dependence, exhibiting unchanged at most temperatures, then they decrease with increasing temperature, and disappears at room temperature. The unstrained ED and EID energies estimated from the PL spectra at 75 and 125 K are plotted as a function of Sn concentration, and the cross-over point of unstrained Ge1-ySny is obtained to be about 6.4%-6.8% Sn by linear fits in the range of Sn content from 0% to 9.0%. Here, some of n-type doped Ge1-ySny samples were used because we did not have as-grown undoped samples for all Ge1-ySny samples. Based on the results at 75 and 125 K with doping correction, the cross-over Sn concentration of unstrained Ge1-ySny from indirect bandgap to direct bandgap might be also about 6.4%-6.8% Sn content at room temperature, which is also in good agreement with previous predictions estimated at 125 and 175 K.