Fig. 3

a Visible-reflected (VIS); b UV-induced visible luminescence (UVL); c Infrared-reflected false colour (IRRFC); d UV-reflected false colour (UVRFC) images of the front central section of C1

a Visible-reflected (VIS); b UV-induced visible luminescence (UVL); c Infrared-reflected false colour (IRRFC); d UV-reflected false colour (UVRFC) images of the front central section of C1