Cooperative Near‐IR to Visible Photon Upconversion in Yb³⁺‐Doped MnCl₂ and MnBr₂: Comparison with a Series of Yb³⁺‐Doped Mn²⁺ Halides

Abstract

Yb3+-doped MnCl2 and MnBr2 crystals exhibit strong red upconversion luminescence under near-infrared excitation around 10 000 cm(-1) at temperatures below 100 K. The broad red luminescence band is centred around 15 200 cm(-1) for both compounds and identified as the Mn2+ 4T1g-->6A1g transition. Excitation with 10 ns pulses indicates that the upconversion process consists of a sequence of ground-state and excited-state absorption steps. The experimental VIS/NIR photon ratio at 12 K for an excitation power of 191 mW focused on the sample with a 53 mm lens is 4.1% for MnCl2:Yb3+ and 1.2% for MnBr2:Yb3+. An upconversion mechanism based on exchange coupled Yb3+-Mn2+ ions is proposed. Similar upconversion properties have been reported for RbMnCl3:Yb3+, CsMnCl3:Yb3+, CsMnBr3:Yb3+, RbMnBr3:Yb3+, Rb2MnCl4:Yb3+. The efficiency of the upconversion process in these compounds is strongly dependent on the connectivity between the Yb3+ and Mn2+ ions. The VIS/NIR photon ratio decreases by three orders of magnitude along the series of corner-sharing Yb3+-Cl--Mn2+, edge-sharing Yb3+-(Cl-)2-Mn2+ to face-sharing Yb3+-(Br-)3-Mn2+ bridging geometry. This trend is discussed in terms of the dependence of the relevant super-exchange pathways on the Yb(3+)-Mn2+ bridging geometry.

Tailored Near‐Infrared Photoemission in Fluoride Perovskites through Activator Aggregation and Super‐Exchange between Divalent Manganese Ions

“…For hexagonal CsMnF 3 (Figure 4i), the MnF 6 octahedra share a corner and a face with a connecting angle of 177°/88°. It has been reported that the exchange interaction between two coupling ions is primarily governed by the overlap of the orbital wavefunctions for linear configuration,40, 43 see Figure 4j. Thus, enhanced coupling between Mn 2+ ions is expected in KMnF 3 and CsMnF 3 because these compounds have nearly linear Mn—F—Mn configuration.…”

“…It should be noted, though, that aggregation would not by itself lead to distinct luminescence38, 39 because there has to be some kind of interaction between the activators. Such interaction reactions between transition metal ions are generally dependent on orbital and ligand geometry 40. In order to obtain a deeper understanding of this, we recorded the temperature‐dependent emission spectra for Mn 2+ ‐doped KMnF 3 , NaMnF 3 , and CsMnF 3 , in which different alkali ions are used to provide different Mn 2+ —Mn 2+ linkage geometry.…”

Transition Metal‐Involved Photon Upconversion

“…The UC efficiency of the exchange‐coupled Mn 2+ –Yb 3+ dimer is configuration geometry‐dependent 33. The ratio of the Mn 2+ UC and the Yb 3+ NIR was taken as a measure of the UC efficiency when excited by a 980 nm laser.…”

Optical temperature sensing by upconversion luminescence of Er doped Bi5TiNbWO15ferroelectric materials

“…Over the past decades, the upconversion (UC) luminescence of rare-earth (RE) have attracted considerable attention in the fields of physics, chemistry, material science and life science because of their wide application such as color displays, 1 short-wavelength lasers, 2 IR quantum counter detectors, 3 optical sensing, 4 optical communications, 5 and biomedical diagnostics. 6 Recently, to achieve larger depth range in tissue and animal imaging, many efforts have been devoting to the development of optical monitoring devices by UC emission.…”

“…Among BLSFs, Bi 5 TiNbWO 15 (BTNW) was typical BLSFs of the intergrowth of Bi 3 TiNbO 9 , which has highest T c , with Bi 2 WO 6 along the c-axis, in which the materials can improve the piezoelectricity retaining a high T c . 20 3 (99.99% Sinopharm Chemical Reagent Co. Ltd.). The raw materials were mixed with the addition of alcohol, dried, heated at 850 • C for 4h.…”