Absolute Internal Quantum Efficiency Research Articles

Evaluation of radiative and non-radiative recombination lifetimes in InGaN quantum wells with different ion-implantation damage

In this study, we have separately evaluated the radiative and non-radiative recombination lifetimes for InGaN quantum well (QW) samples with different amounts of ion-implantation damage, and have investigated their temperature dependence. The radiative and non-radiative recombination lifetimes were calculated from photoluminescence (PL) decay time measured by time-resolved PL measurements, combined with the absolute internal quantum efficiency values estimated by the simultaneous photoacoustic and PL measurements. As a result, the experimentally observed radiative recombination lifetimes are almost the same for all samples, while the non-radiative recombination lifetimes are shorter for samples with larger ion-implantation damage. These findings will lead to a comprehensive understanding of carrier dynamics in InGaN-QW optical devices.

Low temperature absolute internal quantum efficiency of InGaN-based light-emitting diodes

A method to reveal low temperature absolute internal quantum efficiency of an InGaN-based light-emitting diode (LED) is reported. Structural (via scanning electron and atomic force microscopies, x-ray diffraction, and Raman spectroscopy) and optical (via temperature- and power-dependent photoluminescence) properties of InGaN-based blue LEDs are coupled with a channel-based recombination model, which reveals the low temperature absolute internal quantum efficiency of the LED on traditional sapphire and emerging Si (111) substrates as 27.5% and 71.1%, respectively. High low-temperature absolute internal quantum efficiency of the former is attributed to its lower defect density and less strain. Our results show assuming perfect (i.e., 100%) internal quantum efficiency in an InGaN-based LED at low temperatures could be misleading, and using negative thermal quenching properties of defect luminesce bands with a channel-based recombination model can be a method to quantify LED's less than ideal low temperature internal quantum efficiencies.

A Novel Method to Measure Absolute Internal Quantum Efficiency in III-Nitride Semiconductors by Simultaneous Photo-Acoustic and Photoluminescence Spectroscopy

A Novel Method to Measure Absolute Internal Quantum Efficiency in III-Nitride Semiconductors by Simultaneous Photo-Acoustic and Photoluminescence Spectroscopy

Hydrothermal synthesis, characterization, and luminescence of Ca2B2O5:RE (RE = Eu3+, Tb3+, Dy3+) nanofibers

Ca2B2O5:RE (RE = Eu3+, Tb3+, Dy3+) nanofibers were synthesized by the hydrothermal reaction method. The structural refinement was conducted on the base of the X-ray powder diffraction (XRD) measurements. The surface properties of the Ca2B2O5:RE (RE = Eu3+, Tb3+, Dy3+) nanofibers were investigated by the measurements such as the scanning electron microscope (SEM), transmission electron microscope (TEM), and the energy dispersive spectrum (EDS). The nanofiber has a diameter of about 100 nm and a length of several micrometers. The luminescence properties such as photoluminescence excitation (PLE) and emission spectra (PL), decay lifetime, color coordinates, and the absolute internal quantum efficiency (QE) were reported. Ca2B2O5:Eu3+ nanofibers show the red luminescence with CIE coordinates of (x = 0.41, y = 0.51) and the luminescence lifetime of 0.63 ms. The luminescence of Ca2B2O5:Tb3+ nanofibers is green color (x = 0.29, y = 0.53) with the lifetime of 2.13 ms. However, Dy3+-doped Ca2B2O5 nanofibers present a single-phase white-color phosphor with the fluorescence decay of 3.05 ms. Upon near-UV excitation, the absolute quantum efficiency is measured to be 65, 35, and 37 % for Eu3+-, Tb3+-, Dy3+-doped Ca2B2O5 nanofibers, respectively. It is suggested that Ca2B2O5:RE (RE = Eu3+, Tb3+, Dy3+) nanofibers could be an efficient phosphor for lighting and display.

Luminescence and application of red-emitting phosphors of Eu3+-activated R2Zr3(MoO4)9 (R = La, Sm, Gd)

New red-emitting phosphors R2Zr3(MoO4)9:Eu3+ (R = La, Sm, Gd) were prepared using the convenient solid-state reaction method. The samples were characterized by X-ray powder diffraction (XRD) measurements and structural refinements. The luminescence properties were investigated by photoluminescence spectra, decay curves, and absolute internal quantum efficiency (QE). The phosphors exhibited bright red luminescence corresponding to the electric dipole transition 5D0→7F2 at 615 nm under near UV light excitation. The thermal stability of the luminescence was investigated using temperature-dependent intensities at temperatures from 20 to 170°C. The results indicate that Gd2Zr3(MoO4)9:Eu3+ could be potentially considered for lighting due to its qualities, including their excitation spectra, QEs, red color coordinates, and thermal stability.

Preparation, characterization and high quantum efficiency of yellow-emitting CsVO3 nanofibers

The self-activated yellow-emitting CsVO3 nanofibers were prepared by the hydrothermal reaction method. The structural refinement was conducted on the base of XRD measurement. The surface properties of the CsVO3 nanofibers were investigated using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Energy Dispersive Spectrometry (EDS). One of the morphological characterizations is the high length–diameter ratio with diameters of 100–150 nm and lengths of tens of micrometers. The UV–vis absorption spectrum and the electronic band structures of CsVO3 nanofiber show a direct allowed electronic gap with band energy of 2.997 eV. The luminescence properties such as photoluminescence spectra, decay lifetime, color coordinates and the absolute internal quantum efficiency (η) were studied. Notably, CsVO3 nanofibers present a bright yellow luminescence with a high quantum efficiency of 85%. It is suggested that CsVO3 nanofibers could be used for efficient lighting and display.

Determination of the absolute internal quantum efficiency of photoluminescence in GaN co-doped with Si and Zn

The optical properties of high-quality GaN co-doped with silicon and zinc are investigated by using temperature-dependent continuous-wave and time-resolved photoluminescence measurements. The blue luminescence band is related to the ZnGa acceptor in GaN:Si,Zn, which exhibits an exceptionally high absolute internal quantum efficiency (IQE). An IQE above 90% was calculated for several samples having different concentrations of Zn. Accurate and reliable values of the IQE were obtained by using several approaches based on rate equations. The concentrations of the ZnGa acceptors and free electrons were also estimated from the photoluminescence measurements.

Extremely high absolute internal quantum efficiency of photoluminescence in co-doped GaN:Zn,Si

We report on the fabrication of GaN co-doped with silicon and zinc by metalorganic vapor phase epitaxy and a detailed study of photoluminescence in this material. We observe an exceptionally high absolute internal quantum efficiency of blue photoluminescence in GaN:Zn,Si. The value of 0.93±0.04 has been obtained from several approaches based on rate equations.

A simple measurement of the absolute internal quantum efficiency of thin organic films

In this article, we present a simple method for the determination of the absolute internal quantum efficiency of thin organic dye layers. The basic idea is the comparison of the luminescence of the film with the reflection of a white diffusive reflectance standard measured at one angle with a simple spectrofluorometer. The method is compared to the procedure of de Mello [J. C. de Mello, H. F. Wittmann and R. H. Friend, Adv. Mater. 9, 230 (1997)], which uses an integrating sphere. As examples, the quantum yields of films of the two perylene derivatives N,N′-dimethylperylene-3,4:9,10-dicarboximide and 3,4,9,10-perylenetetracarboxylic dianhydride, are determined.

Temperature-dependent photoluminescence and electroluminescence properties of polysilanes

We have determined an absolute internal quantum efficiency (ηint) of various alkyl- and phenyl-based polysilanes by photoluminescence (PL) in the temperature range between 10 and 300 K. Larger ηint have been obtained usually in dialkyl-based polysilanes (e.g., 90% at 10 K and 27% at 300 K for polydihexylsilane (PDHS)). The smaller ηint of polymethylphenylsilane (PMPS) turned out to be due to the resonant energy-transfer between main- and side-chains. By introducing branching into Si main-chain in the PMPS, the effect of electronic delocalization on the luminescence characteristics has been investigated. A polydimethylsilane (PDMS) deposited on an indium tin oxide (ITO)-covered glass was electroluminesced (EL) at both 77 and 300 K, indicating a possibility for light emitting applications.

Quantum Efficiency and Radiative Lifetime of the Band-to-Band Recombination in Heavily Dopedn-Type GaAs

The dependence of the absolute internal quantum efficiency and the radiative lifetime of the band-to-band recombination on the impurity concentration for melt-grown heavily doped $n$-type GaAs crystals have been determined from measurements of photoluminescence and optical-absorption spectra, the excess-carrier lifetime, and the external efficiency. It is shown that the observed external efficiency at 2\ifmmode\times\else\texttimes\fi{}${10}^{18}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ is determined by the combined effects of the position and slope of the absorption edge, the hole lifetime, the surface loss, and the photon reabsorption of the emitted radiation. The radiative lifetime exhibits a minimum at 1.5\ifmmode\times\else\texttimes\fi{}${10}^{18}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ because of the effects of the impurity on the slope and position of the absorption edge. This is in contrast to the case of lightly doped nondegenerate crystals in which the radiative lifetime is inversely proportional to the impurity concentration.