Photoluminescence upconversion at GaAs/InGaP2 interfaces driven by a sequential two-photon absorption mechanism

This paper reports on the results of an investigation into the nature of photoluminescence upconversion at GaAs/InGaP2 interfaces. Using a dual-beam excitation experiment, we demonstrate that the upconversion in our sample proceeds via a sequential two-photon optical absorption mechanism. Measurements of photoluminescence and upconversion photoluminescence revealed evidence of the spatial localization of carriers in the InGaP2 material, arising from partial ordering of the InGaP2. We also observed the excitation of a two-dimensional electron gas at the GaAs/InGaP2 heterojunction that manifests as a high-energy shoulder in the GaAs photoluminescence spectrum. Furthermore, the results of upconversion photoluminescence excitation spectroscopy demonstrate that the photon energy onset of upconversion luminescence coincides with the energy of the two-dimensional electron gas at the GaAs/InGaP2 interface, suggesting that charge accumulation at the interface can play a crucial role in the upconversion process

Analytical model for the intensity dependence of 1500 nm to 980 nm upconversion in Er3+^{3+}: a new tool for material characterization

We propose a simplified rate-equation model for the 1500 nm to 980 nm upconversion in Er$^{3+}$. The simplifications, based on typical experimental conditions as well as on conclusions based on previously published more advanced models, enable an analytical solution of the rate equations, which reproduces known properties of upconversion. We have compared the model predictions with intensity-dependent measurements on four samples with different optical properties, such as upconversion-luminescence yield and the characteristic lifetime of the $^4I_{13/2}$ state. The saturation of the upconversion is in all cases well-described by the model over several orders of magnitude in excitation intensities. Finally, the model provides a new measure for the quality of upconverter systems based on Er$^{3+}$ -- the saturation intensity. This parameter provides valuable information on upconversion parameters such as the rates of energy-transfer upconversion and cross-relaxation. In the present investigation, we used the saturation intensity to conclude that the differences in upconversion performance of the investigated samples are mainly due to differences in the non-radiative relaxation rates.Comment: 8 pages, 6 figures, to be submitted to PR

Efficient oxide phosphors for light upconversion; green emission from Yb3+ and Ho3+ co-doped Ln(2)BaZnO(5) (Ln = Y, Gd)

This is the author's accepted version of the article. The final published article can be found here: http://dx.doi.org/10.1039/C0JM01652

Sub-quadratic dependence of visible upconversion on infra-red direct luminescence decay owing to static energy-transfer upconversion

Because of their broadband luminescence, TM-ion-doped materials are of high interest for applications as tunable and short-pulse lasers. Systems with a d1 electron configuration possess only one excited 3d level and excited-state absorption into higher-lying 3d levels is impossible. One of these d1 systems, Ti:sapphire has become the most successful tunable and short-pulse laser system to date. Mn6+ is a promising d1 ion for a tunable laser system. In BaSO4, near-infrared emission from Mn6+ was observed. The room-temperature stimulated-emission cross section is larger than the excited-state-absorption cross section in the spectral range 920-1600 nm [1], i.e., as a laser material BaSO4:Mn6+ can offer a broad tuning range.\ud Here we report on the first epitaxial growth of Mn6+-doped BaSO4 layers. Growth techniques such as the melt growth fail, because barium sulphate has a phase transition at 1090°C and exhibits thermal decomposition at 1590°C. Therefore, we grew BaSO4 substrate crystals by the flux method. The Mn6+ ions tend to reduce to Mn5+ at T  620°C. We used a CsCl-KCl-NaCl solvent [2] for the LPE of BaSO4:Mn6+. This solvent has a low solidification temperature of 480°C and the growth process could be performed at temperatures well below 620°C. The nominal Mn6+ concentration was up to 0.8 mol%. High quality, lack of large-size inclusions, and low defect concentration were achieved. These Mn6+-doped BaSO4 layers were investigated spectroscopically by absorption, emission, and luminescence-excitation measurements at room temperature. Excitation at 800 nm leads to broadband Mn6+ emission between 850 and 1600 nm. Currently, we investigate the lasing potential of our BaSO4:Mn6+ layers.\ud [1] T.C. Brunold, H.U. Güdel, S. Kück, G. Huber, JOSA B 14, 2373 (1997).\ud [2] D. Ehrentraut, M. Pollnau, J. Cryst. Growth 234, 533 (2002)

Quantum Transduction of Telecommunications-band Single Photons from a Quantum Dot by Frequency Upconversion

The ability to transduce non-classical states of light from one wavelength to another is a requirement for integrating disparate quantum systems that take advantage of telecommunications-band photons for optical fiber transmission of quantum information and near-visible, stationary systems for manipulation and storage. In addition, transducing a single-photon source at 1.3 {\mu}m to visible wavelengths for detection would be integral to linear optical quantum computation due to the challenges of detection in the near-infrared. Recently, transduction at single-photon power levels has been accomplished through frequency upconversion, but it has yet to be demonstrated for a true single-photon source. Here, we transduce the triggered single-photon emission of a semiconductor quantum dot at 1.3 {\mu}m to 710 nm with a total detection (internal conversion) efficiency of 21% (75%). We demonstrate that the 710 nm signal maintains the quantum character of the 1.3 {\mu}m signal, yielding a photon anti-bunched second-order intensity correlation, g^(2)(t), that shows the optical field is composed of single photons with g^(2)(0) = 0.165 < 0.5.Comment: 7 pages, 4 figure

Population mechanisms of the green Er3+:LiYF4 laser

In computer simulations the mechanisms that lead to room-temperature continuous-wave green upconversion lasing in Er3+:LiYF4 are investigated. The rate-equation system considers the full erbium level scheme up to 2H9/2, ground-state depletion, excited-state absorption on the pump and laser wavelengths, three interionic processes, stimulated emission, and the crystal and resonator data of the experiments. Experimental results performed at the University of Hamburg, Germany, are reproduced in the simulation. The influence of different parameters as pump wavelength, absorption cross sections, interionic parameters, dopant concentration, and temperature is investigated. An avalanche effect which exploits the strong cross relaxation from the upper laser level and the upconversion from 4I13/2 leads to an efficient population of the upper laser level. At higher dopant concentrations the cross relaxation becomes detrimental to stimulated emission due to the depletion of the upper laser level. This concentration dependence can be considered as a general behavior of rare-earth-doped avalanche lasers