Free regulation of luminous color of Ln-CQDs synthesized with citric acid-chelated Ln ions as the precursor

Abstract

In order to avoid the shortcoming of the luminescence singleness of traditional carbon quantum dots (CQDs), the free regulation of luminous color of CQDs were achieved by doping lanthanide ions in the study. Firstly, Eu3+-doped carbon quantum dots (Eu-CQDs) were synthesized with citric acid-chelated europium ions as the precursor by a hydrothermal method. Doped europium ions existed in the Eu(III) state in Eu-CQDs and the prepared Eu-CQDs showed two parts of the photoluminescence (PL) spectrum, which originated from the blue emission of CQDs and the characteristic photoluminescence of Eu3+ ions, respectively. With an increase in the concentration of Eu3+, the intensity of Eu3+ characteristic emission showed an enhanced trend, but the intensity of the characteristic peaks of CQDs decreased. The CIE coordinate confirmed the continuous regulation of the luminous color of CQDs from blue to red. When the concentration of Eu3+ ions was 6%, the ratio of PL intensity between Eu3+ ions and CQDs was higher, thus generating purple-red light emission. In addition, the dual fluorescent characteristics of Eu-CQDs showed quite different responses to different environment pH values. When pH = 6, the CCT value of Eu(6%)-CQDs was 2156 K, indicating a good red light performance. The white light emission of CQDs could be realized by co-doping 5 mol% Eu3+ and 2 mol% Tb3+ in CQDs and adjusting the environmental pH = 7. The CCT value of doped CQDs was 5115 K, indicating a good neutral white light performance.