Energy Transfer Upconversion Parameter Research Articles

Quadrature frequency resolved spectroscopy of upconversion photoluminescence in GeGaS:Er3+: I. Determination of energy transfer upconversion parameter

The article presents the formulas of quadrature frequency resolved spectroscopy (QFRS) on the upconversion photoluminescence (UCPL) of rare-earth (RE) doped materials on the general M-level model. The formulas are derived in matrix-equation form with the first-order perturbation on the rate equations at the M energy-levels of RE ion. The QFRS spectra for three different UCPL processes, i.e., the excited state absorption (ESA), energy transfer upconversion (ETU) and photon avalanche (PA) via cross relaxation process (CRP) in a particular case of M = 3 are demonstrated with the respective salient features of the excitation power dependence. We have measured the QFRS on the UCPL (4S3/2 → 4I15/2) by systematically varying Er-doping in Ge28.1Ga6.3S65.6 chalcogenide glass from 0.01 to 0.5 at.% as well as 975 nm excitation power. Thereby the relaxation rates k1 at the intermediate level 4I11/2, k2 at the top level 4S3/2 and ETU parameter w are determined as a function of Er concentration. The UCPL dynamics on the basis of the formulas for the 3-level model is interpreted in terms of the determined parameters.

Stochastic Model of Energy-Transfer Processes Among Rare-Earth Ions. Example of Al2O3:Tm3+

Energy-transfer processes strongly affect the performance of lanthanide-doped photonic devices. In this work, we introduce a simple stochastic model of energy-transfer processes and successfully apply it to the example of cross-relaxation (CR) and energy-transfer upconversion (ETU) in amorphous Al2O3:Tm3+ waveguides on silicon intended for lasers operating at ∼2 μm. The stochastic model is based on the rate-equation formalism and considers two spectroscopically distinct ion classes, namely single ions and ions with neighbors (pairs and clusters), with the corresponding ion fractions being dependent on the doping concentration. We prove that a more accurate description of the luminescence properties of amorphous Al2O3:Tm3+ is obtained when accounting for the presence of these distinct ion classes. Based on the developed model, we derive microscopic CR and ETU parameters of CCR = 5.83 × 10–38 cm6 s–1, CETU1 = 0.93 × 10–40 cm6 s–1, and CETU2 = 7.81 × 10–40 cm6 s–1, and determine the laser quantum efficiency ...

Upconversion Dynamics in Er3+‐Doped Gd2O2S: Influence of Excitation Power, Er3+ Concentration, and Defects

Upconversion (UC) enables the conversion of lower energy to higher energy photons and has gained interest for the application in solar cells and nanocrystal biolabels. Er3+‐doped Gd2O2S is a highly promising UC material for applications. A record UC quantum yield of 12% was recently measured in Gd2O2S doped with 10% Er3+ upon monochromatic excitation into the 4I13/2 state at 1510 nm for moderate excitation densities (700 W m−2). In this work, the focus is on the dynamics of the infrared (4I13/2, ≈1500 nm) to near‐infrared (4I11/2, ≈1000 nm) UC luminescence in Er3+‐doped Gd2O2­S. On the basis of luminescence spectra (emission and excitation), UC emission decay curves, and rate equation modeling, it is shown that energy transfer upconversion (ETU) is the mechanism responsible for the 4I11/2 UC luminescence, and the ETU parameter for Gd2O2S:10%Er3+ is determined to be W ETU = 6.3 × 10−19 cm3 s−1. The UC dynamics depend on the Er3+ concentration and, similar to triplet–triplet annihilation UC in organic materials, on the excitation power. The results highlight the subtle balance between desired energy transfer processes leading to ETU and undesired energy migration to quenching sites. The overall UC efficiency is dependent not only on the material and composition but also on the synthesis process.

Determination of the macroscopic upconversion parameter in Er^3+-doped transparent glass ceramics

A simple rate equation model is used to determine the macroscopic upconversion parameter of a heavily erbium-doped oxyfluoride transparent glass ceramic. The fraction of initially excited ions in the metastable state among erbium ions partitioned in the nanocrystallite phase is found and the decay of the 4S3/2 level is used to determine the upconversion parameter. The macroscopic energy-transfer upconversion parameter is found to be approximately 4×10−18cm3s−1, in good agreement with other erbium-doped fluoride materials.

Fluorescence quantum efficiency measurements in the presence of Auger upconversion by the thermal lens method.

Mode-mismatched thermal lens (TL) measurements in Cr3+-doped fluoride crystals (LiSrAIF6 and LiSrGaF6) are reported. A nonlinear increase of the TL signal, and decrease of quantum efficiency, with increasing excitation power was observed and attributed to energy-transfer upconversion (ETU). Assuming an upconversion rate that is proportional to the excited-state population, Wup = gammaN(e), the theoretical model developed fits the experimental data well. The ETU parameters (gamma) were determined with unprecedented accuracy for low Cr concentrations. Thermo-optical parameters (K, ds/dT) were also obtained.

Decorrelation of luminescent decay in energy-transfer upconversion

A method is presented that gives access to an important parameter in the spectroscopic investigation of energy-transfer upconversion (ETU), namely the fraction of ions that fulfill the condition to participate in ETU, independent of the physical nature of this condition. We exploit the fact that downconversion and upconversion luminescence probe different classes of ions. For ions with a qualified energy-level scheme, a simple analytical solution derives. The method is independent of the pump and ETU parameters.

Upconversion losses in Nd-doped fluoroarsenate glasses

In this work we report the infrared to visible upconversion processes in Nd-doped fluoroarsenate glasses that produce green, orange, and red emissions together with the dynamics of the 4F 3/2 state. The visible emissions can be attributed to transitions from the 4G 7/2 excited state populated by energy transfer upconversion (ETU). It was found that ETU processes involving two Nd 3+ ions in the 4F 3/2 state reduce the energy storage capacity through the reduction of the fluorescence lifetimes of the 4F 3/2 state. From the analysis of the temporal evolution of the infrared emission from the 4F 3/2 state we have estimated the macroscopic ETU parameter for the samples studied.

Energy transfer processes inEr3+-doped andEr3+,Pr3+-codoped ZBLAN glasses

We present a detailed characterization of energy transfer processes in Er3+-doped and Er3+,Pr3+-codoped ZBLAN bulk glasses. For several Er3+ (0.25–8.75 mol%) and Pr3+ (0.25–1.55 mol%) concentrations, we investigate energy transfer upconversion (ETU) and cross relaxation in Er3+ as well as energy transfer (ET) from Er3+ to the Pr3+ codopant. The measured parameters of ETU from the Er3+ 4I13/2 and 4I11/2 levels are comparable to those of LiYF4:Er3+. ETU from 4I13/2, in particular, possesses a factor of 3 larger probability than ETU from 4I11/2. The parameters of ET from the Er3+ 4I13/2 and 4I11/2 levels to the Pr3+ codopant are larger than the corresponding ETU parameters. ET effectively quenches the 4I13/2 intrinsic lifetime of 9 ms down to 20 us for the highest Er3+ and Pr3+ concentrations investigated, and is more efficient than ET from 4I11/2, because the corresponding absorption transition in Pr3+ has a large oscillator strength and back transfer is inhibited by fast multiphonon relaxation from the corresponding Pr3+ level. In both cases, the ET parameters depend on Er3+ concentration in a similar way as the ETU parameters but depend only weakly on Pr3+ concentration. This shows that energy migration within the Er3+ 4I13/2 and 4I11/2 levels is fast. The presented results are important for the choice of the appropriate operational regime of the erbium 3-um fiber laser.