Spectroscopy and Dynamics of Re⁴⁺ Near-IR-to-Visible Luminescence Upconversion

Abstract

Intense visible upconversion luminescence is observed in a Re(4+)-doped low-phonon host material, Cs(2)ZrCl(6), with excitation in the near-infrared. The upconversion excitation wavelength, temperature, power, and time dependence is studied using variable-temperature absorption and luminescence spectroscopies, and modeled using a three-level set of coupled nonlinear rate equations. On the basis of analysis of these data, energy-transfer upconversion is shown to be the dominant mechanism responsible for this phenomenon. The main properties of this upconversion mechanism are correlated to properties of the Re(4+) electronic structure, in particular the large energy gaps, the small excited-state distortions, and the lack of cross-relaxation pathways for radiationless decay. These properties make this ion attractive for upconversion phosphor and laser materials applications, and two potential upconversion laser schemes are proposed. The contributions of these same properties to the photoredox chemistry of Re(4+) and related d(3) ions are discussed.

Transition Metal‐Involved Photon Upconversion

“…The cross‐relaxation of 1 T 2 → 3 T 2 + 3 A 2 → 3 T 1 quenches the 1 T 2 → 3 A 2 green UC emission of Ni 2+ in MgF 2 when pumped by 752.5 nm laser,21 see Figure 4c. Re 4+ was the first TM ion studied in UC material22 and the first TM ion to show RT UC phenomenon owing to the relaxation of the spin selection rules by its strong spin‐orbit coupling 23. The UC‐emitting state Γ 7 ( 2 T 2g ) has a branching ratio of 1:2 for luminescence to ground state Γ 8 ( 4 A 2g ) relative to the intermediate excited state Γ 8 ( 2 E g ).…”

Host sensitized near infrared to visible photon upconversion in 1% Re4+ doped Cs2NaYbBr6

“…1. We have previously shown that Re 4+ in an octahedral F − , Cl − , and Br − environment is capable of NIR to VIS photon upconversion [5][6][7]. This is due to the fact that the Re 4+ excitations shown in Fig.…”

“…1, being simple spin flips, couple very weakly to the lattice, and bear a lot of similarity to the f-f excitations in lanthanides. In Re 4+ doped Cs 2 ZrCl 6 [6] and Cs 2 ZrBr 6 [7] excitation into the Re 4+ [ 2 E g / 2 T 1g ] multiplet between 8000 and 10 000 cm −1 leads to red Re 4+ [ 7 ( 2 T 2g )] emission at all temperatures between 10 and 300 K. This is a rather inconvenient excitation region, both in the laboratory and for possible applications.…”

Nanopartikel für die Aufwärtskonversion

“…UCProzesse konnten in einer großen Anzahl von mit Über-gangsmetallionen dotierten Wirtgittern, z. B. für Ti 2+ -, [17,18] Ni 2+ -, [19][20][21][22] Mo 3+ -, [23,24] Re 4+ - [23,25,26] oder Os 4+ -dotierte Festkörper, [27][28][29][30] nachgewiesen werden. Auch Actinoid-dotierte Materialien wurden auf ihre UC-Eigenschaften untersucht.…”