Quantum cutting mechanism in NaYF4:Tb3+, Yb3+

Energy Transfer Studies in Tb3+-Yb3+ Co-Doped Phosphate Glasses

Detailed optical properties of Tb3+-Yb3+ co-doped phosphate glasses were performed based on their emission spectra and decay measurements. Under blue excitation of Tb3+ at 488 nm, the intensity of Yb3+ emissions gradually enhanced upon increasing the Yb3+ content until 1 mol% indicated an energy transfer from Tb3+ to Yb3+. Otherwise, under near infrared excitation of Yb3+ at 980 nm, these glasses exhibit intense green luminescence, which led to cooperative sensitization of the 5D4 level of Tb3+ ions. A cooperative energy transfer mechanism was proposed on the basis of the study on the influence of Yb3+ concentration on up-conversion emission intensity, as well as the dependence of this up-conversion intensity on near infrared excitation power. Moreover, the temporal evolution of the up-conversion emissions have been studied, which was in positive agreement with a theoretical model of cooperative up-conversion luminescence that showed a temporal emission curve with rise and decay times of the involved levels.

Ytterbium-Doped CsPbCl3 Quantum Cutters for Near-Infrared Light-Emitting Diodes

Exploring highly efficient near-infrared (NIR) emitting materials is desirable for the advancement of next-generation smart NIR light sources. Different from most reported Cr³⁺-doped emitters with far-red emissions, Yb³⁺-activated phosphors are expected to yield pure NIR (∼1000 nm) light. Herein, a new hot-injection route using all metal-oleate salts to fabricate Yb³⁺-doped CsPbCl₃ perovskite nanocrystals (PeNCs) is reported for the first time, which produce PeNC-sensitized Yb³⁺ NIR emission with photoluminescence quantum yields (PLQYs) higher than 100%. With the help of temperature-dependent PL spectra, femtosecond transient absorption spectra, and time-resolved PL spectra, it is evidenced that the in situ produced intrinsic shallow trap states in a CsPbCl₃ host play a key role in facilitating the picosecond nonradiative cooperative energy transfer from PeNCs to two Yb³⁺ dopants simultaneously. Using the optimized Yb³⁺:CsPbCl₃ quantum cutters, a phosphor-converted NIR light-emitting diode (pc-NIR-LED) is fabricated, exhibiting an external quantum efficiency of 2%@28 mA, a high NIR output irradiance of 112 mW/cm²@400 mA, and excellent long-term stability. Finally, the designed pc-NIR-LED is demonstrated to have great potential as an invisible night-vision light source.

Dramatic Enhancement of Quantum Cutting in Lanthanide-Doped Nanocrystals Photosensitized with an Aggregation-Induced Enhanced Emission Dye

Applications of multiphoton processes in lanthanide-doped nanophosphors (NPs) are often limited by relatively weak and narrow absorbance. Here, the concept of an ultimate photosensitization by aggregation-induced enhanced emission (AIEE) dyes to overcome this limitation is introduced. Because AIEE dyes do not suffer from concentration quenching, they can fully cover the NP surface at high density to maximize absorbance while passivating the surface. This concept is applied to multiphoton down-conversion by quantum cutting. Specifically, coating Yb³⁺/Tb³⁺-doped NPs with an AIEE dye designed for efficient energy transfer and attachment to the NPs produces a 2260-fold enhancement of multiphoton down-conversion by quantum cutting with remarkable photostability. In a prototypical application, the quantum cutting of UV photons to near-infrared photons that are matched to the band gap of a silicon solar cell produces an average 4% increase in efficiency under concentrated solar illumination. This provides a general strategy for NP photosensitization that can be applied to both multiphoton up- and down-conversion.

NIR Downconversion and Energy Transfer Mechanisms in Tb3+/Yb3+ Codoped Na5Lu9F32 Single Crystals

Tb³⁺/Yb³⁺ codoped Na₅Lu₉F₃₂ single crystals with near-infrared (NIR) emission are achieved by an improved Bridgman approach. Energy transfer from Tb³⁺ to Yb³⁺ ions is affirmed by the photoluminescence (PL) emission spectra and decay curves characterization. On the basis of the analysis of energy transfer rate dependence on the Yb³⁺ concentration, the interaction between Tb³⁺ and Yb³⁺ ions in Na₅Lu₉F₃₂ single crystals is confirmed through the one-to-one energy transfer process. Results demonstrate that the prepared Na₅Lu₉F₃₂ single crystals might be promising candidates to convert sunlight to improve the performance of the silicon solar cells.

Tb3+- and Yb3+-doped novel KBaLu(MoO4)3 crystals with disordered chained structure showing down- and up-conversion luminescence

Tb³⁺/Yb³⁺ co-doped KBaLu(MoO₄)₃ with a highly disordered structure consisting of chains induces high color purity of primary green luminescence.

Experimental evidence for quantum cutting co-operative energy transfer process in Pr3+/Yb3+ ions co-doped fluorotellurite glass: dispute over energy transfer mechanism

Pr³⁺/Yb³⁺ doped materials have been widely reported as quantum-cutting materials in recent times. However, the question of the energy transfer mechanism in the Pr³⁺/Yb³⁺ pair in light of the quantum-cutting phenomenon still remains unanswered. In view of that, we explored a series of Pr³⁺/Yb³⁺ co-doped low phonon fluorotellurite glass systems to estimate the probability of different energy transfer mechanisms. Indeed, a novel and simple way to predict the probability of the proper energy transfer mechanism in the Pr³⁺/Yb³⁺ pair is possible by considering the donor Pr³⁺ ion emission intensities and the relative ratio dependence in the presence of acceptor Yb³⁺ ions. Moreover, the observed results are very much in accordance with other estimated results that support the quantum-cutting phenomena in Pr³⁺/Yb³⁺ pairs, such as sub-linear power dependence of Yb³⁺ NIR emission upon visible ∼450 nm laser excitation, integrated area of the donor Pr³⁺ ion's visible excitation spectrum recorded by monitoring the acceptor Yb³⁺ ion's NIR emission, and the experimentally obtained absolute quantum yield values using an integrating sphere setup. Our results give a simple way of estimating the probability of an energy transfer mechanism and the factors to be considered, particularly for the Pr³⁺/Yb³⁺ pair.

Plasmon enhanced near-infrared quantum cutting of KYF₄: Tb³⁺, Yb³⁺ doped with Ag nanoparticles

Novel quantum cutting (QC) phosphor KYF4:  Tb3+, Yb3+ doped Ag nanoparticles (NPs) was prepared by using the sol-gel method. Plasmon enhanced near-infrared (NIR) QC involving Yb3+ ion at 975 nm (2F5/2→2F7/2) emission was achieved under the excitation of 374 nm (7F6→5D3) and 485 nm (7F6→5D4) of Tb3+ ions, respectively. The effect of Ag NPs on NIR QC luminescence was investigated, and the results show that QC luminescence intensity first increases, then decreases with the increase of the Ag NPs concentration. The maximum enhancement factor is about 1.9 when the concentration of Ag NPs is 0.5%. Our study may have potential application in the field of silicon-based solar cells.

An active-core/active-shell structure with enhanced quantum-cutting luminescence in Pr-Yb co-doped monodisperse nanoparticles

Monodisperse Pr(3+)/Yb(3+):NaGdF₄@NaYF₄ active-core/inert-shell nanoparticles, which exhibit efficient near-infrared quantum-cutting luminescence, are successfully prepared. In order to relieve the adverse effect caused by concentration quenching in the core, the extra Yb(3+) ions are introduced into the shell, forming an active-core/active-shell structure which leads to a much intensified near-infrared emission.

Quantum cutting in Pr3+-Yb3+ codoped chalcohalide glasses for high-efficiency c-Si solar cells

Downconversion materials, which can convert one high-energy photon to two low-energy photons, have provided a promising avenue for the enhancement of solar cell efficiency. In this work, the Pr3+-Yb3+ codoped 25GeS2-35Ga2S3-40CsCl chalcohalide glasses were synthesized in a vacuumed silica ampoule by the melting-quenching technique. Under 474 nm excitation, the visible and near-IR emission spectra reveal the energy transfer from Pr3+ to Yb3+ ions, resulting in the intense 1008 nm near-IR emission for the c-Si solar cells. By tuning the excitation laser power, it is determined that one visible photon has been cut into two near-IR photons during the energy transfer process. With the help of an integrated sphere, the real quantum yields of near-IR emissions were calculated. For the 0.2Pr2S3-0.2Yb2S3 (in mol.%) codoped chalcohalide glass, the quantum yield equals 10.8%. Although this efficiency is still low, this result will open a new route to realize the efficient spectral modification of the solar spectrum.

Controlled synthesis, photoluminescence, and the quantum cutting mechanism of Eu3+ doped NaYbF4 nanotubes

Eu³⁺ doped NaYbF₄ nanotubes show quantum cutting down-conversion under 393 nm excitation. An improved method is proposed to calculate Judd–Ofelt parameters and to study the energy transfer mechanism.