Graphene oxide (GO) is a promising material for energy storage device applications. Modified Hummers method (MHM) has been used to prepare GO films from graphite flakes by Sol-Gel method. With the aid of bridging agent dimethyldichlorosiline, structurally fine GO films were prepared. Fourier transform and infra-red (FTIR) spectrum of the GO thin film possesses absorption bands at 461, 594, 670, 803, 1020, 1243, 1457, 1544, 1627, 2850, 2926 and 3429 cm−1. A sharp OH− absorption band was revealed at 3429 cm−1. Two vibrational bands were noticed in the Raman spectrum for pure graphite flakes at 1578 and 2718 cm−1. However, for GO, five Raman vibrational bands were unveiled at 413, 1344, 1597, 2697 and 2945 cm−1. Among these bands, the mode at 1344 cm−1 was assigned to D-band and 1597 cm−1 was assigned to G-band. Compared to D-band, G-band was dominated for the GO films. Several times of centrifugation and ultra-sonication process have aided to obtain more intensity of G-band. In addition, 2D and D + G bands were also revealed in the GO films. X-ray diffraction (XRD) analysis was confirmed that a sharp peak at 10.64 degrees leads to the formation of GO thin film.

Oxyfluoride glasses doped with 2, 5, 8, 12, 16 and 20 mol% of ytterbium (Yb3+) ions have been prepared by the conventional melt-quenching technique. Their optical, thermal and thermo-mechanical properties were characterized. Luminescence intensity at 1020 nm under laser excitation at 920 nm decreases with increasing Yb3+ concentration, suggesting a decrease in the photoluminescence quantum yield (PLQY). The PLQY of the samples was measured with an integrating sphere using an absolute method. The highest PLQY was found to be 0.99(11) for the 2 mol% Yb3+: glass and decreases with increasing Yb3+ concentration. The mean fluorescence wavelength and background absorption of the samples were also evaluated. Upconversion luminescence under 975 nm laser excitation was observed and attributed to the presence of Tm3+ and Er3+ ions which exist as impurity traces with YbF3 starting powder. Decay curves for the Yb3+: 2F5/2 → 2F7/2 transition exhibit single exponential behavior for all the samples, although lifetime decrease was observed for the excited level of Yb3+ with increasing Yb3+ concentration. Also observed are an increase in the PLQY and a slight decrease in lifetime with increasing the pump power. Finally, the potential of these oxyfluoride glasses with high PLQY and low background absorption for laser cooling applications is discussed.

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