Synthesis, structure, and optical properties of colloidal GaN quantum dots

Abstract

Colloidal chemistry was used to synthesize GaN quantum dots. A GaN precursor, polymeric gallium imide, {Ga(NH)3/2}n, which was prepared by the reaction of dimeric amidogallium with ammonia at room temperature, was heated in trioctylamine at 360 °C for one day to produce GaN nanocrystals. The GaN particles were separated, purified, and partially dispersed in a nonpolar solvent to yield transparent colloidal solutions that consisted of individual GaN particles. The GaN nanocrystals have a spherical shape and mean diameter of about 30±12 Å. The spectroscopic behavior of colloidal transparent dispersion has been investigated and shows that the band gap of the GaN nanocrystals shifts to slightly higher energy due to quantum confinement. The photoluminescence spectrum at 10 K (excited at 310 nm) shows band edge emission with several emission peaks in the range between 3.2 and 3.8 eV, while the photoluminescence excitation spectrum shows two excited-state transitions at higher energies.

Synthesis of blue-shifted luminescent colloidal GaN nanocrystals through femtosecond pulsed laser ablation in organic solution

“…On the other hand, the optical absorption spectrum of GaN-NPs via fs PLA shows strong absorption behavior starting from 285 nm (4.35 eV) to shorter wavelengths (i.e., higher energies). This large blue shift of *1 eV in the optical absorption spectrum compared to bulk GaN material indicates a reduction in nano-sized range occurring due to quantum size effects of the carrier confinement (Leppert et al 1998;Mićić et al 1999;Bagga et al 2003;Li and Wang 2005).…”

“…By limiting the size of a material to smaller than the doubled exciton Bohr radius, the material starts showing novel optical and structural properties like blue shift in optical absorption and PL spectra in comparison with the band gap emission of bulk material (Ramvall et al 1998;Gyger et al 2014). Crystalline GaN quantum dots provide enhanced carrier confinement-induced blue shift (Leppert et al 1998;Mićić et al 1999;Klimov et al 2000;Preschilla et al 2000;Miyamura et al 2002) and allow one to design core-shell nanostructures (Reiss et al 2009). GaN QDs are demonstrated high sensitivity in gas sensing, e.g., H 2 and ethanol and biocompatible candidate in bio-imaging as luminescence probes (Fan et al 2014).…”

“…A number of nanocrystalline GaN studies were reported through some grown techniques (Mićić et al 1999;Borsella et al 2001;Miyamura et al 2002;Zhuang et al 2013;Gyger et al 2014). GaN quantum dots were grown by Miyamura et al (2002) through low-pressure metalorganic chemical vapor deposition.…”

Colloidal III–V Nitride Quantum Dots

“…According to the previous reports, Mićić et al [40] still used {Ga(NH)3/2}n to prepare the GaN but they added trioctylamine (TOA) and hexadecylamine (HDA) during the heating process. The HDA could improve hydrophobicity of the GaN surface because of its less sterical hinderance and much dense surface cap.…”

“…Finally, the GaN nanoparticles are formed after the further growth and the size of the particles depends on the reaction time and temperature. The precursor contains polymeric gallium imide [40,41] and gallium cupferron with hexamethyldisilazane, [42] etc. The selection of the precursor is very important for successful growth of colloidal GaN quantum dots.…”