Abstract
A spectroscopic study of the population mechanisms in erbium-doped amorphous aluminum oxide up to the H11/22/S3/24 levels is performed. Via luminescence decay measurements, absorption and emission spectra, and a Judd–Ofelt analysis, we determine luminescence lifetimes, radiative and nonradiative decay-rate constants, and branching ratios of the Er3+ intermanifold transitions. With a continuous-wave pump-probe technique, the excited-state absorption (ESA) spectrum is recorded between 900 and 1800 nm and the cross sections of the ESA transitions I13/24→I9/24, I13/24→F9/24, and I11/24→F7/24 are determined. The microparameters and efficiencies of resonant and phonon-assisted energy-migration and energy-transfer upconversion (ETU) processes among Er3+ ions occurring from the first and second excited states are evaluated. From the ratio of the S3/24 and F9/24 luminescence intensities as a function of Er3+ concentration, we prove the existence and quantify the macroscopic ETU coefficient of the two-phonon-assisted ETU process (I13/24,I11/24)→(I15/24,F9/24).
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