Top-down synthesis techniques are the most commonly used methods for synthesizing graphene oxide (GO) and graphene oxide quantum dots (GOQDs). In most cases, multistep procedures (at least two steps) or long reaction times (more than 3 h) are required. Herein, a temperature controlled, facile, one-pot solvothermal method is demonstrated that allows us to selectively synthesize pure GO and pure GOQDs within 1.5 hours, respectively. More importantly, the final product of either GO and GOQDs with different sizes can be easily controlled by tuning reaction temperatures or the precursor reactant ratios. GOQDs approximately 2.5 nm in size show excellent photoluminescence that can be utilized for bioimaging or selective detection of trace amounts of Eu³⁺ and Tb³⁺ from their respective mixtures with other rare earth and/or transition metal ions, at sub-ppm concentrations.