Upconversion and anti‐Stokes Processes with f and d Ions in Solids

Abstract

For Abstract see ChemInform Abstract in Full Text.

Enhancement of up-conversion efficiency by combining rare earth-doped phosphors with PbS quantum dots

“…The 4 Ii3/ 2 -> 4 Ii5/ 2 Er 3+ ions transition (1520 nm) is clearly observed, independently of the presence of QDs. Furthermore, the shape of the peak agrees with experiments reported by Auzel [12]. The same intensity for both cases (with and without QDs) is the result of the much stronger concentration of the codopant Yb 3+ ion compared to the Er 34 " ion.…”

“…The emission of the PbS-QDs coincides with the ground state absorption of the Er 3+ ( 4 Ii 5 / 2~^4 Ii3/2)-Consecutive absorption as well as energy transfer-based UC processes takes place from this first excited state to a second one [12]. However, the PTIR545/F-UC is not so appropnate for solar cells, because of the combination of Yb 3+ and Er 3^ The UC effect occurs because of the absorption of 980 nm-photons in Yb 3+ , and after the deexcitation of this state, the energy is transferred to the Er 3+ , so that it competes with silicon for the NIR photons with wavelengths of between 900 and 1100 nm [13].…”

Multi-ion cooperative processes in Yb3+ clusters

“…Experimental CL results are essential clues to understanding the nature of cooperative quantum transitions, such as the energy shifts of pair levels from their parent single-ion levels, the selection rules obeyed by the cooperative transitions, and quantum entanglement in multibody systems. [1][2][3] The first CL was demonstrated with a pair of excited Yb 31 ions in 1970. 4 Since then, the CL from Yb 31 -dimers has been studied extensively due to their unique 4f 13 configuration with two multiplets ( 2 F 5/2 , 2 F 7/2 ) and the relatively large absorption cross-section at ,980 nm.…”

Photon energy upconversion through thermal radiation with the power efficiency reaching 16%

“…Photon energy upconversion from the infrared to visible region was first demonstrated in the early 1960's by second-harmonic generation 8 and two-photon photoluminescence 9 , which require intense coherent excitation sources and deliver low-power conversion efficiencies. Coupled 4f ions, benefiting from their ladder-like energy levels that facilitate photon absorption and subsequent energy transfer processes, offer higher power conversion efficiencies under moderate excitation densities through excited-state absorption or energy transfer upconversion 2,[10][11][12] . Very recently, introduction of molecular dye sensitizers enables upconversion upon excitation within a broad absorption range of the dyes 13 .…”

“…Ionic sensitizers are introduced to a host to absorb infrared photons and transfer energy to the host lattice through multiphonon relaxation 11 . Phonon accumulation in the host lattice boosts the temperature and intensifies the thermal radiation, for which a large fraction of photons have higher energy than the incident ones.…”