Quantum cutting through downconversion in rare-earth compounds (original) (raw)
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Downconversion: a new route to visible quantum cutting
Journal of Alloys and Compounds, 2000
To obtain vacuum ultraviolet (VUV) phosphors with quantum efficiencies higher than 100%, the concept of downconversion is used. In a downconversion process a VUV photon is split into two visible photons by making use of energy transfer between different rare earth 31 31 31 31 31 ions. Two examples of downconversion couples are discussed, viz. the Gd -Eu couple and the Er -Gd -Tb system. X-ray powder diffraction. LiGdF has the inverse scheelite 4 0925-8388 / 00 / $ -see front matter © 2000 Elsevier Science S.A. All rights reserved. PII: S0925-8388( 99 )00755-0 5 7 1(c) illustrates the possibility of cross relaxation between a D → F transition. J J quantum cutting ion. It can be calculated that several J 5 10 31 4 energy migration step, however, all D levels can become transitions from the 4f 5d state of Er to different F J J 4 3 1 populated by multiphonon relaxation from higher levels. and G states overlap Gd transitions from the ground J 5 6 6 6
Visible quantum cutting in Eu3+-doped gadolinium fluorides via downconversion
Journal of Luminescence, 1999
Emission of two photons of visible light per absorbed vacuum ultraviolet photon (known as quantum cutting) is reported for LiGdF : Eu> and GdF : Eu>. For every Gd> ion excited in the G ( levels (around 50 000 cm\) or higher, two visible photons can be emitted due to D ( PF ( transitions on two Eu> ions. The "rst Eu> ion is excited into the D level by cross relaxation of the energy corresponding to the G ( PP ( transition on Gd>. The second Eu> ion is excited by direct energy transfer of the remaining energy from Gd> (P ( ) to Eu>. It is shown that this two-step energy transfer process is very e$cient at room temperature. Since this process is the opposite of the well-known upconversion process, we call it downconversion.
Research of green emitting rare-earth doped materials as potential quantum-cutter
Optical Materials, 2008
Because the energy of vacuum ultraviolet (VUV) photons emitted by xenon plasma discharge is more than twice that of visible photons, quantum cutting appears to be a promising process in rare-earth doped materials in order to obtain efficient phosphors for mercury free lighting devices as well as for plasma display panels. With an aim of application, it is important to take into account the emitting color of the developed new phosphors. Most of the time, this leads to use systems with at least two kinds of rare earth ions: one of them playing the role of energy sensitizer, and the other one being in charge of emitting the light of the suitable color. We focus our attention on green rare-earth doped materials. In order to get very efficient phosphors, it is not only necessary to get the highest possible quantum yield, but also to have a material characterized by a strong absorption in the VUV range. Borate and fluoride matrices doped with Dy 3+ / Tb 3+ couples of ions are selected according to the position of the 5d band of dysprosium as green emitters.
Luminescent materials with quantum efficiency larger than 1, status and prospects
Journal of Luminescence, 2002
In this paper, the status of research on quantum cutters is reviewed. Three possible mechanisms will be dealt with in detail and compared to each other. None of the mechanisms identified can be applied in combination with a Hg discharge, as all materials require photons of wavelengths shorter than provided by the main low-pressure Hg emission line. r * quantum cutting using host lattice states, * quantum cutting on single ions, * quantum cutting on ion pairs.
Applied Physics Letters, 2010
Downconversion of one visible photon to two near-infrared photons may increase the efficiency of c-Si solar cells by 30%. The lanthanide ion couple Er 3+-Yb 3+ is well known for efficient upconversion but for the reverse process, downconversion, fast multiphonon relaxation from the 4 F 7/2 level has been shown to compete with downconversion. Here we report efficient downconversion for the Er-Yb couple in Cs 3 Y 2 Br 9. The low phonon energy in this bromide host suppresses multiphonon relaxation and efficient two step energy transfer from the 4 F 7/2 level of Er 3+ is observed and results in strong 1000 nm emission from Yb 3+. Based on emission spectra and luminescence life time measurements an intrinsic downconversion efficiency close to 200% is determined.
Near-Infrared Quantum Cutting for Photovoltaics
Advanced Materials, 2009
Sustainable energy production based on the direct conversion of energy radiated by the sun into useable forms is expected to gain importance because it may be the only source capable of generating sufficient energy to meet the long-term worldwide energy demand. The capacity of photovoltaic cells to convert sunlight into electricity makes them prime candidates for this task, but at present the contribution of photovoltaic energy is limited due to its relatively high cost per kilowatt-hour. A reduction in price may be achieved by either lowering the production cost or increasing the conversion efficiency. State-ofthe-art commercial crystalline Si (c-Si) solar cells dominate the market and have energy efficiencies around 15%. The main source of energy loss (over 70%) is related to the spectral mismatch of incident solar photon energies to the energy gap (E g ) of a solar cell. Solar cells generate a single electron-hole pair upon absorbing a photon above the bandgap. Photons with energies lower than the bandgap are not absorbed, and for photons with energies exceeding the bandgap, the excess energy is lost as heat during the fast thermalization of the 'hot' charge carriers. Taking these sources of energy loss into account, the maximum energy efficiency that can be reached is known as the Shockley-Queisser limit. For the solar spectrum, the limit is 30% for a solar cell with a bandgap of 1.1 eV (close to that of c-Si).
Vacuum-ultraviolet spectroscopy and quantum cutting for Gd3+ in LiYF4
Physical Review B, 1997
A systematic spectroscopic study of the 4 f 7 energy levels of Gd 3ϩ in LiYF 4 in the vacuum-ultraviolet spectral region (50 000-70 000 cm Ϫ1) is reported. Using energy-level calculations, all observed spectral lines could be assigned to free-ion term symbols ͑including term symbols with unusually high L and J, e.g., a 2 Q 23/2 level around 67 000 cm Ϫ1 ͒. From the 6 G J levels around 50 000 cm Ϫ1 quantum cutting ͑or two-photon luminescence, photon-cascade emission͒ is observed: the emission of a red photon due to the 6 G J → 6 P J transition is followed by the emission of an ultraviolet photon due to the 6 P J → 8 S 7/2 transition.
Multi-photon quantum cutting in Gd2O2S:Tm3+ to enhance the photo-response of solar cells
Light: Science & Applications, 2015
Conventional photoluminescence (PL) yields at most one emitted photon for each absorption event. Downconversion (or quantum cutting) materials can yield more than one photon by virtue of energy transfer processes between luminescent centers. In this work, we introduce Gd 2 O 2 S:Tm 31 as a multi-photon quantum cutter. It can convert near-infrared, visible, or ultraviolet photons into two, three, or four infrared photons of ,1800 nm, respectively. The cross-relaxation steps between Tm 31 ions that lead to quantum cutting are identified from (time-resolved) PL as a function of the Tm 31 concentration in the crystal. A model is presented that reproduces the way in which the Tm 31 concentration affects both the relative intensities of the various emission lines and the excited state dynamics and providing insight in the quantum cutting efficiency. Finally, we discuss the potential application of Gd 2 O 2 S:Tm 31 for spectral conversion to improve the efficiency of next-generation photovoltaics.
Space-separated quantum cutting with silicon nanocrystals for photovoltaic applications
Nature Photonics, 2008
For optimal energy conversion in photovoltaic devices (electricity to and from light) one important requirement is that the full energy of the photons is used. However, in solar cells, a single electron -hole pair of specific energy is generated when the incoming photon energy is above a certain threshold, with the excess energy being lost to heat. In the so-called quantum-cutting process, a high-energy photon can be divided into two, or more, photons of lower energy. Such manipulation of photon quantum size can then very effectively increase the overall efficiency of a device. In the current work, we demonstrate (space-separated) photon cutting by silicon nanocrystals, in which nearby Er 31 ions and neighbouring nanocrystals are used to detect this effect.
Understanding and tuning blue-to-near-infrared photon cutting by the Tm3+/Yb3+ couple
Light: Science & Applications, 2020
Lanthanide-based photon-cutting phosphors absorb high-energy photons and ‘cut’ them into multiple smaller excitation quanta. These quanta are subsequently emitted, resulting in photon-conversion efficiencies exceeding unity. The photon-cutting process relies on energy transfer between optically active lanthanide ions doped in the phosphor. However, it is not always easy to determine, let alone predict, which energy-transfer mechanisms are operative in a particular phosphor. This makes the identification and design of new promising photon-cutting phosphors difficult. Here we unravel the possibility of using the Tm3+/Yb3+ lanthanide couple for photon cutting. We compare the performance of this couple in four different host materials. Cooperative energy transfer from Tm3+ to Yb3+ would enable blue-to-near-infrared conversion with 200% efficiency. However, we identify phonon-assisted cross-relaxation as the dominant Tm3+-to-Yb3+ energy-transfer mechanism in YBO3, YAG, and Y2O3. In NaYF4...