Absorption spectra, defect site distribution and upconversion excitation spectra of CaF2/SrF2/BaF2:Yb3+:Er3+ nanoparticles

• Published in: Journal of alloys and compounds Vol. 834; p. 155165
• Main Authors: Balabhadra, Sangeetha, Reid, Michael F., Golovko, Vladimir, Wells, Jon-Paul R.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 05-09-2020; Elsevier BV
• Subjects: Absorption; Absorption spectra; Barium fluorides; Calcium ions; Cluster centres; Clusters; Cubic site; Erbium; Excitation spectra; Fluorescence; Nanoparticles; Semiconductor lasers; Strontium fluorides; Upconversion; Upconversion and excitation dynamics; Ytterbium; Nanoparticles; Absorption; Cubic site; Cluster centres; Upconversion and excitation dynamics
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2020.155165

We report studies of the Yb3+ site distribution in Er3+ co-doped upconverting alkaline earth fluoride nanoparticles using high-resolution absorption measurements. It is found that Yb3+ single ion cubic (Oh) sites and preferentially formed clusters are the dominant centres for moderate dopant concentrations. At higher concentrations, and for larger particle sizes, a minority C4v(F−) centre is also observed. Furthermore, the behaviour of Yb3+ cluster centres, whose primary absorption band is centred at 10205 cm−1 (in near resonance with 980 nm laser diodes) was studied by tuning the metal cation in the host lattice from Ca2+→Sr2+→Ba2+. For co-doped materials, with heterogeneous cluster centres, Er3+ upconversion fluorescence was observed upon selective excitation of Yb3+, resulting in a strong visible emission from 2H11/2, 4S3/2 and 4F9/2 multiplets. By monitoring the Er3+ fluorescence, whilst scanning a laser through the wavelength dependent Yb3+ absorption, we obtain an excitation spectrum for these heterogeneous cluster centres. Spectral features associated with excited state absorption as well as significant deviation from the linear absorption spectra are observed.
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•Ytterbium and erbium codoped nanoparticles were prepared by the hydrothermal method.•We report on the site distribution of the Yb3+ ions.•The behaviour of Yb3+ cluster centres was studied by tuning the metal cation in the alkaline earth fluoride host.•Upconversion excitation spectra were obtained for the heterogeneous Yb–Er cluster centres.