Svette Reina Merden Santiago

Photo-induced Doping in GaN Epilayers with Graphene Quantum Dots

We demonstrate a new doping scheme where photo-induced carriers from graphene quantum dots (GQDs) can be injected into GaN and greatly enhance photoluminescence (PL) in GaN epilayers. An 8.3-fold enhancement of PL in GaN is observed after the doping. On the basis of time-resolved PL studies, the PL enhancement is attributed to the carrier transfer from GQDs to GaN. Such a carrier transfer process is caused by the work function difference between GQDs and GaN, which is verified by Kelvin probe measurements. We have also observed that photocurrent in GaN can be enhanced by 23-fold due to photo-induced doping with GQDs. The improved optical and transport properties from photo-induced doping are promising for applications in GaN-based optoelectronic devices.

Enhanced Conversion Efficiency of III–V Triple-junction Solar Cells with Graphene Quantum Dots

Graphene has been used to synthesize graphene quantum dots (GQDs) via pulsed laser ablation. By depositing the synthesized GQDs on the surface of InGaP/InGaAs/Ge triple-junction solar cells, the short-circuit current, fill factor, and conversion efficiency were enhanced remarkably. As the GQD concentration is increased, the conversion efficiency in the solar cell increases accordingly. A conversion efficiency of 33.2% for InGaP/InGaAs/Ge triple-junction solar cells has been achieved at the GQD concentration of 1.2 mg/ml, corresponding to a 35% enhancement compared to the cell without GQDs. On the basis of time-resolved photoluminescence, external quantum efficiency, and work-function measurements, we suggest that the efficiency enhancement in the InGaP/InGaAs/Ge triple-junction solar cells is primarily caused by the carrier injection from GQDs to the InGaP top subcell.

Origins of excitation-wavelength-dependent photoluminescence in WS2 quantum dots

We report the photoluminescence studies of pristine and diethylenetriamine-doped (DETA-doped) WS2 quantum dots (QDs) synthesized by pulsed laser ablation. The DETA-doped WS2 QDs revealed a notable improvement of the luminescence quantum yield from 0.1% to 15.2% in comparison to pristine WS2 QDs. On the basis of the photoluminescence (PL) under different excitation wavelengths and the emission-energy dependence of PL dynamics, we suggest that the excitation-wavelength-dependent (excitation-wavelength-independent) PL for pristine (DETA-doped) WS2 QDs is attributed to the recombination of carriers from the localized (delocalized) states.

Correction: Tunnel injection from WS2 quantum dots to InGaN/GaN quantum wells

Correction for ‘Tunnel injection from WS2 quantum dots to InGaN/GaN quantum wells’ by Svette Reina Merden Santiago et al., RSC Adv., 2018, 8, 15399–15404.

Temperature-dependent photoluminescence in nitrogen-doped graphene quantum dots

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.

Enhanced Performance of GaN-based Ultraviolet Light Emitting Diodes by Photon Recycling Using Graphene Quantum Dots.

Graphene quantum dots (GQDs) with an average diameter of 3.5 nm were prepared via pulsed laser ablation. The synthesized GQDs can improve the optical and electrical properties of InGaN/InAlGaN UV light emitting diodes (LEDs) remarkably. An enhancement of electroluminescence and a decrease of series resistance of LEDs were observed after incorporation of GQDs on the LED surface. As the GQD concentration is increased, the emitted light (series resistance) in the LED increases (decreases) accordingly. The light output power achieved a maximum increase as high as 71% after introducing GQDs with the concentration of 0.9 mg/ml. The improved performance of LEDs after the introduction of GQDs is explained by the photon recycling through the light extraction from the waveguide mode and the carrier transfer from GQDs to the active layer.

Efficient carrier transfer from graphene quantum dots to GaN epilayers

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.

Electron injection from graphene quantum dots to poly(amido amine) dendrimers

The steady-state and time-resolved photoluminescence (PL) are used to study the electron injection from graphene quantum dots (GQDs) to poly(amido amine) (PAMAM) dendrimers. The PL is enhanced by depositing GQDs on the surfaces of the PAMAM dendrimers. The maximum enhancement of PL with a factor of 10.9 is achieved at a GQD concentration of 0.9 mg/ml. The dynamics of PL in the GQD/PAMAM composite are analyzed, evidencing the existence of electron injection. On the basis of Kelvin probe measurements, the electron injection from the GQDs to the PAMAM dendrimers is accounted for by the work function difference between them.