Quantum cutting in CaYAlO4: Pr3+, Yb3+

Efficient X-ray excited short-wavelength infrared phosphor

X-ray combined with short-wavelength infrared (SWIR) phosphors, that can make full advantage of the deeper tissue penetration of SWIR light, can be used as a fluorescent probe to realize biological imaging of deep tissues; they are, however, limited by their lower luminescence efficiency. Here, we describe a strategy to synthesize highly efficient SWIR luminescence phosphor based on the efficient energy transfer process between charge transfer state (CTS) of Yb³⁺ and the ⁶I_J levels of Gd³⁺ as well as Gd³⁺-Gd³⁺. This allows us to achieve 813.8 mW/m² of SWIR luminescence power in Yb³⁺-BaGd_0.6Y_0.4ZnO₅ (BGYZ). Our results highlight that this approach to enhance SWIR luminescence may provide new opportunities for the deep-tissue biological imaging.

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.

Crystal-site engineering control for the reduction of Eu(3+) to Eu(2+) in CaYAlO4: structure refinement and tunable emission properties

In this article, Eu-activated CaYAlO4 aluminate phosphors were synthesized by a solid-state reaction. Under UV light excitation, characteristic red line emission of Eu(3+) was detected in the range of 570-650 nm. In addition, we introduced crystal-site engineering approach into the CaYAlO4 host through incorporation of Si(4+)-Ca(2+) to replace Al(3+)-Y(3+), which would shrink the AlO6 octahedrons, accompanied by the expansion of CaO9 polyhedron, and then enable the partial reduction of Eu(3+) to Eu(2+). The crystal structure and underlying mechanism have been clarified on the basis of the Rietveld refinement analysis. The PL spectra of Ca0.99+xY1-xAl1-xSixO4:Eu0.01 (x = 0-0.30) exhibit both green emission of Eu(2+) (4f(6)5d(1)-4f(7), broadband around 503 nm) and red-orange emission of Eu(3+) ((5)D0-(7)F1,2, 593 and 624 nm) under UV light excitation with a quantum yield of 38.5%. The CIE coordinates of Ca0.99+xY1-xAl1-xSixO4:Eu0.01 (x = 0-0.30) phosphors are regularly shifted from (0.482, 0.341) to (0.223, 0.457) with increasing x, which would expand the application of Eu. Furthermore, this investigation reveals the correlations of structure and property of luminescent materials, which would shed light on the development of novel phosphors suitable for lighting and display applications.

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.