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Quadrature Frequency Resolved Spectroscopy of Upconversion Photoluminescence in GeGaS:Er3 ; II. Elucidating Excitation Mechanisms of Red Emission besides Green Emission
Authors: Aoki Takeshi | Střižík Lukáš | Hrabovský Jan | Wágner Tomáš
Year: 2016
Type of publication: ostatní - přednáška nebo poster
Page from-to: nestránkováno
Titles:
Language Name Abstract Keywords
eng Quadrature Frequency Resolved Spectroscopy of Upconversion Photoluminescence in GeGaS:Er3 ; II. Elucidating Excitation Mechanisms of Red Emission besides Green Emission The green emission of the wavelength ~550 nm excited by upconversion of photoluminescence at 980 nm or 800 nm in Er3+-doped materials is accompanied by rather weak red emission ~660 nm corresponding to the 4F9/2 → 4I15/2 transition of Er3+. Though various excitation mechanisms of the red emission are proposed, they are still speculative and need more precise verification. Here we report the QFRS (quadrature frequency resolved spectroscopy) of the red emission, which is excited through the 4I11/2 intermediate level by 975 nm laser and demonstrates singly-peaked, featureless and slightly slower lifetime distribution (open circles) at the excitation photon-flux density Φ ca 2.3x10^21 cm−2 s−1 in contrast to the green emission (solid circles) in Fig. 1. As the populations of the two intermediate levels 4 I13/2 and 4I11/2 are normally higher than those of the green- and red-emitting levels, we adopt the excitation schema of the 5-level model omitting the level 4I9/2 (Fig. 2). The red-emitting (R) level 4F9/2 is mostly populated through the 3 channels; 1) radiative and nonradiative relaxation from 4S3/2, 2) the excited state absorption ESA2: 4I13/2 → 4F9/2 and 3) the energy transfer upconversion ETU2 with the energy-transfer parameter ν: 4I11/2 + 4I13/2 → 4I15/2 + 4F9/2, whereas the green-emitting (G) level 4S3/2 is solely excited from 4I11/2 by ESA1 and/or ETU1 with the parameter w [3]. Simulation of the QFRS spectra (curves in Fig. 1) carried out on linearized non-linear rate-equations of the 5-level model and curve-fitting to the data of different Er3+ concentration and Φ give the excitation cross-section σ2 of ESA2 and ν with the composite lifetimes (total relaxation rates) at 4I13/2 and 4F9/2 for the red emission as well as w with the composite lifetimes at 4I11/2 and 4S3/2 for the green emission. Upconvesion photoluminescence; Quadrature frequency resolved spectroscopy; Er-doped chalcogenide glass; Green and red emissions; 5-level model; Nonlinear Regression

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