Here, the hysteresis and negative photoconductivity (NPC) in arginine-doped tungsten disulfide (WS2) quantum dots (QDs) synthesized via microwave heating method were investigated and discussed. WS2 solution and arginine were used as the QDs and dopant sources, respectively. The structure of arginine-doped WS2 QDs was analyzed by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The synthesized arginine-doped WS2 QDs displays a diameter of less than 10 nm and demonstrates an excitation-dependent photoluminescence (PL) behavior. The PL intensity of arginine-doped WS2 QDs displayed an 18 folds increase compared to the pristine WS2 QDs. The electrical transport demonstrated a p-type doping as a result of the introduction of arginine in WS2 QDs. I-V measurements in varying environment and laser illumination were utilized to investigate the hysteresis and negative photoconductivity (NPC) phenomena in arginine-doped WS2 QDs. Based on this analysis, the hysteresis and NPC are proposed to originate from the interaction of water and/or gas molecules adsorbed on the surface of arginine-doped WS2 QDs. This optoelectronic study of WS2 QDs is expected to contribute for the potential development and performance improvement of WS2-QD-based devices.
In this research, we have synthesized graphene quantum dots (GQDs) concurrent with N doping by pulsed laser ablation (PLA) of graphene oxide (GO) with urea. The synthesized N-doped GQDs (N-GQDs) with an average diameter less than 5 nm and N/C atomic ratio of 33.4% have been demonstrated by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), respectively. The temperature dependence of the photoluminescence (PL) intensity in GQDs and N-GQDs were investigated. The PL intensity of the GQDs was quenched monotonously with increasing temperature. However, an unusual enhancement of PL intensity in N-GQDs was observed with temperatures within the temperature range of around 50-150 K. We suggest that the distinct dependence of PL intensity of N-GQDs on the temperature originated from a carrier transfer mechanism between the N-dopant induced state (energy level) and quantum-dot emitting states. This study is rendered advantageous in understanding the effect of N-doping on the luminescence properties of GQDs useful for the potential applications.
The photoluminescence (PL) properties in GaN epilayers were investigated after depositing graphene quantum
dots (GQDs) on the GaN surface. A seven-fold enhancement of the PL intensity in GaN was observed in the GQD/GaN
composite. On the basis of the PL dynamics, the enhancement of PL in GaN is attributed to the carrier transfer from
GQDs to GaN. Such a carrier transfer is caused by the work function difference between GQDs and GaN, evidencing by
Kelvin probe measurement. The improved PL is promising toward applications in the GaN-based optoelectronic devices.
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