This work presents the luminescent, structural and morphological properties of
carbon dots (CDs) synthesized on ZnAl2O4 (ZAO) by a simple combustion method.
The samples were annealed at different temperatures (600, 700, 800, and 900C)
in order to change the concentration and size of the CDs on ZAO. The XRD
patterns indicated that the annealed samples present a cubic phase (spinel
structure). According to the TEM analysis, the CDs on ZAO (CZAO) have a particle
size in the range of 2.0-4.0 nm. The annealing treatment, allowed to tune their
luminescence emission from green (517 nm) to red (650 nm) under excitation with
blue light (455 nm). Yellow, orange, and red phosphorescence were observed for
the first time from CDs. The green/yellow and orange/red phosphorescence lasted
5 min and 15 min, respectively, which are the longest phosphorescence times
reported for CDs. It is proposed that CDs’ luminescence originates from the deep levels formed after the annealing treatment. Due to the color tunability presented
by the CDs in fluorescence and phosphorescence, the CZAO samples can be
useful for applications in biolabeling, bioimaging, lighting, and signaling for
buildings and roads.