Carbon nanoparticles (CNPs) attract a lot of interest because of their numerous unique properties. The advantage of photoluminescent CNPs is the simplicity of synthesis and surface modification, photostability and low cytotoxicity. In connection with the variety of methods of synthesis and the possibility of changing the initial materials, it is expedient to study the factors that affect the properties of the obtained particles. Recently, much attention has been paid to CNPs based on citric acid and ethylenediamine. This is due to the fact that such particles have a high quantum yield and can be an alternative of semiconductor quantum dots. In this work, we report the influence of the form of the diamine and the pH of the CNPs solutions on the photoluminescent properties. We also studied the stability of CNPs diluted solutions in time. As a result of the work, we determined that the optimal pH of CNPs solutions are close to neutral, which makes it possible to use the CNPs in biological objects.