The PL signal was collected by a lens with a focal distance f = 100 mm and then focused by a second lens to optical multimodal fiber with an aperture of 900 μm. The PL signal was analyzed by a spectrophotometer (Acton Spectra Pro, SP-2300). Two long pass filters, positioned between the second lens and an optical fiber, were used to remove the scattered laser light. The PL spectra were measured with an integration time of 0.2 seconds. The in situ PL setup was placed in a glove box with an inert Ar atmosphere.