Enhancement of Photon Upconversion in Rare Earth-Doped Carbon Quantum Dots

Among the various types of quantum dots, Carbon Quantum Dots (CQDs) have emerged as a particularly promising class of nanomaterials. CQDs are characterized by their tunable photoluminescence, high chemical stability, low toxicity, and excellent biocompatibility, making them suitable for a wide range of applications, including bioimaging, sensing, drug delivery, and energy-related devices. Recent research has focused on enhancing the optical properties of CQDs through doping with rare earth elements, which introduces unique photoluminescence properties due to their distinct electronic configurations and energy transitions. Photon upconversion, a process where lower-energy photons are absorbed and re-emitted as higher-energy photons, is a key area of interest in CQD research. This phenomenon is particularly useful in applications that require high-energy ultraviolet light, such as bioimaging and photocatalysis. The ability of CQDs to exhibit photon upconversion, alongside their traditional downconversion photoluminescence, adds to their versatility and potential for innovative applications. The objective of this study is to synthesize and characterize pure and rare earth-doped Carbon Quantum Dots (CQDs) using a hydrothermal method with gelatin as the precursor. The research aims to investigate the photoluminescent properties of these CQDs, with a particular focus on their photon upconversion capabilities and emission stability. By exploring the effects of doping and synthesis conditions on the optical characteristics of CQDs, the study seeks to enhance their potential for applications in fields such as bioimaging, fluorescent marking, solar cell efficiency enhancement, and other technologies requiring stable and reliable luminescence. The ultimate goal is to demonstrate the suitability of these synthesized CQDs for various scientific and practical applications, contributing to advancements in nanomaterial research and technology.

The hydrothermal bottom-up method for synthesizing Carbon Quantum Dots (CQDs) involves dissolving 0.5 grams of gelatin in 25 mL of doubly deionized water with continuous stirring to create a uniform solution. This solution is then transferred into a 50 mL Teflon-lined autoclave, which is placed in a muffle furnace set to 160°C. The mixture undergoes a hydrothermal reaction under controlled heat and pressure for 4 hours, converting the gelatin into CQDs. After heating, the autoclave is allowed to cool gradually, stabilizing the synthesized CQDs with distinctive optoelectronic properties.

Gelatin-based pure and doped Carbon Quantum Dots (CQDs) were synthesized using the hydrothermal method, and their photoluminescent and up-conversion properties were studied. Photoluminescence was observed at different excitation frequencies. At an excitation wavelength of 314 nm, the emission wavelengths for P-CQD, C-CQD, and L-CQD were 395 nm, 402 nm, and 398 nm, respectively. For an excitation wavelength of 341 nm, the emissions were 402 nm, 422 nm, and 417 nm. Photon up-conversion was examined using a 420 nm excitation, showing emission frequency variations with doping.

The synthesized gelatin-based pure and doped CQDs exhibited distinct photoluminescent and up-conversion properties, with emission wavelengths varying according to the excitation frequencies and types of doping. The observed shifts in emission wavelengths, especially under up-conversion at 420 nm excitation, demonstrate that doping influences the optical behavior of CQDs. This tunability of emission frequencies is particularly promising for frequency conversion applications, such as enhancing the spectral absorbance range of solar cells, potentially improving their efficiency by enabling better utilization of the solar spectrum.