A facile method was developed to synthesize fluorescent carbon-dot–Eu³⁺ hybrid composites (CD–Eu–HCs) by one-pot hydrothermal methods. The prepared composites demonstrate unique dual fluorescence which originates from the blue emission of the CDs and intrinsic photoluminescence of the Eu³⁺ ions, respectively. Moreover, such dual fluorescent characteristics show quite different responses for different pH value environments and have been developed in a ratiometric pH sensor. Lastly, they can realize white light emission by co-doping of Tb³⁺ and the color temperature becomes tunable by adjusting the relative proportion of Eu³⁺.