Hongying Peng

Spectroscopic and energy transfer studies of Eu3+ centers in GaN

Photoluminescence (PL), photoluminescence excitation (PLE), and time-resolved PL spectroscopies have been carried out at room temperature and 86K on transitions from D25, D15, and D05 excited states to numerous FJ7 ground states of Eu-doped GaN films grown by conventional solid-source molecular beam epitaxy (MBE) and interrupted growth epitaxy MBE. Within the visible spectral range of 1.8–2.7eV, 42 spectral features were observed and assignments were attempted for each transition. PL and PLE indicate that four Eu3+ centers exist in the GaN lattice whose relative concentration can be controlled by the duration of growth interruption. The energy levels for these four sites are self-consistently obtained, and time-resolved photoluminescence measurements reveal details about the radiative and nonradiative relaxations of excitation among these levels. The data indicate a near-resonant cross relaxation among these sites. The D25 and D15 states are observed to decay nonradiatively by filling the D05 state with c...

Optical characterization of Eu-doped β-Ga2O3 thin films

Europium-doped β-Ga2O3 thin films were grown on double-side polished c-axis (0001) sapphire substrates by pulsed laser deposition at 850°C. Transmission measurements of the films revealed a sharp band edge with a band gap at 5.0eV. The films exhibited intense red emission at 611nm (2.03eV) due to the transitions from D05 to F27 levels in europium, with intensities that increased with the concentration of europium. Time-resolved photoluminescence measurements revealed a temperature-insensitive lifetime of 1.4ms, which is much longer than the lifetimes of europium luminescence observed in GaN hosts.

Effect of optical excitation energy on the red luminescence of Eu3+ in GaN

Photoluminescence (PL) excitation spectroscopy mapped the photoexcitation wavelength dependence of the red luminescence (D05→F27) from GaN:Eu. Time-resolved PL measurements revealed that for excitation at the GaN bound exciton energy, the decay transients are almost temperature insensitive between 86 K and 300 K, indicating an efficient energy transfer process. However, for excitation energies above or below the GaN bound exciton energy, the decaying luminescence indicates excitation wavelength- and temperature-dependent energy transfer influenced by intrinsic and Eu3+-related defects.

Spin-Cast Deposition of CdSe-CdS Core-Shell Colloidal Quantum Dots on Doped GaAs Substrates: Structural and Optical Characterization

The detailed study of the effects of spin recipe and GaAs substrate doping (i.e., semi-insulating, n-type, or p-type) on the structural and optical properties of spin-cast CdSe-CdS core-shell CQDs provides insight into the surface adsorption and charge transfer mechanisms that will influence any potential optoelectronic device. The hypotheses of this study are: i) it is possible to establish spin-casting recipes that yield a thin film of CQDs with large surface density and uniform size, and ii) it is possible to control the optical response of CQDs by varying the GaAs substrate doping to influence charge transfer processes. As a result of these measurements, we have been able to demonstrate a strong dependence of spin-cast CQD structural properties on the doping type of the GaAs substrate, as well as evidence from measured optical properties to support the idea that hot carriers photoexcited in the GaAs substrate are transferred either to the CQD surface states through organic surface ligands or directly to confined states within the CQD.

GaN:Eu Interrupted Growth Epitaxy (IGE): Thin Film Growth and Electroluminescent Devices

Abstract : The GaN:RE phosphor development plays a major role in the GaN:RE AC thick dielectric electroluminescent (TDEL) device optimization. In this paper we report on EL devices fabricated using Eu-doped GaN red phosphors films grown by interrupted growth epitaxy (IGE). IGE consists of a sequence of ON/OFF cycles of the Ga and Eu beams, while the N2 plasma is kept constant during the entire growth time. IGE growth of GaN:Eu resulted in significant enhancement in the Eu emission intensity based primarily at 620.5nm. The increase in the material crystallinity observed with the IGE phosphors appears to be the dominant cause of the emission enhancement. Thick dielectric EL devices fabricated on glass substrates using IGE-grown GaN:Eu have resulted in luminance of ~1000 cd/m2.

Time-resolved spectroscopic analyses of Eu3+ clusters in GaN

Time-resolved photoluminescence has been employed to study carrier relaxation dynamics of Eu3+ clusters in GaN. The results indicated that at least two types of Eu3+ clusters formed in the host, which show the similar lifetime of 5D2, 5D1 and 5D0 upper state levels but give quite different red emission intensity. Full-text article is not available.