Efficient three-step sequential three-photon near-infrared (NIR) quantum cutting in Tm3+-doped transparent oxyfluoride glass ceramics has been demonstrated, where an absorbed blue photon could be cut into three NIR photons at 1190, 1460, and 1800 nm with quantum yield greater than unity. On the basis of static and dynamic photoemission, monitored excitation, and time-resolved fluorescence spectra, we investigate in detail the underlying optoelectronic mechanism. Further development of an efficient triply-cutting material might open up a path towards ultra-efficient photonic devices, which enables more photons emitted than absorbed in the excitation process.
The infrared quantum cutting phenomena, which is an international hot research field, of Er1.0P5O14 noncrystalline glass are studied by the present paper for the first time. The 1537.0nm infrared fluorescence of Er1.0P5O14 noncrystalline glass is confirmed to be the multi-photon quantum cutting fluorescence by computation and comparison between absorption and excitation spectra. It is found that the 4I13/2→4I15/2 quantum cutting fluorescence is very strong, induced by the excited 2H11/2, 4G11/2, and 4G9/2 energy levels. Its mechanism is thoroughly analyzed based on the calculation of spontaneous emission rates, nonradiative multiphonon relaxation rates and energy transfer rates. It is found the strong downconversion energy transfers {2H11/2→4I9/2,4I15/2→4I13/2},{4G11/2→4I13/2, 4I15/2→2H11/2},{4G9/2→4F7/2,4I15/2→4I13/2} 和 {4G9/2→4I13/2, 4I15/2→2H11/2} are responsible for the strong infrared three-photon and four-photon quantum cutting fluorescence of Er1.0P5O14 noncrystalline glass. The present research is significant for enhancing solar cell efficiency.
Abstract Optical modulation is a crucial operation in photonics for network data processing with the aim to overcome information bottleneck in terms of speed, energy consumption, dispersion and cross-talking from conventional electronic interconnection approach. However, due to the weak interactions between photons, a facile physical approach is required to efficiently manipulate photon-photon interactions. Herein, we demonstrate that transparent glass ceramics containing LaF3: Tm3+ (Er3+) nanocrystals can enable fast-slow optical modulation of blue/green up-conversion fluorescence upon two-step excitation of two-wavelengths at telecom windows (0.8–1.8 μm). We show an optical modulation of more than 1500% (800%) of the green (blue) up-conversion fluorescence intensity, and fast response of 280 μs (367 μs) as well as slow response of 5.82 ms (618 μs) in the green (blue) up-conversion fluorescence signal, respectively. The success of manipulating laser at telecom windows for fast-slow optical modulation from rear-earth single-doped glass ceramics may find application in all-optical fiber telecommunication areas.
We present a theoretical scheme for laser cooling in Tm3+-doped oxy-fluoride glass ceramic (GC). Tm3+-doped GC has a unique combination of high chemical and mechanical stability related to the oxide glass and low phonon energy of the fluoride nanocrystals, which trap a majority of Tm3+ ions. This unique property of GC makes it attractive for a number of applications. The effective embedding of rare-earth ions in the crystalline phase with low phonon energy provides high quantum efficiency for the F43→H63 transition in the Tm3+ ions participating in the cooling cycle.
The efficiency of single-junction solar cells is limited to about 30% (the Shockley-Queisser limit). Spectral mismatch losses (transparency to low-energy photons, thermalization of high-energy photons) strongly contribute to lowering the maximum efficiency. To reduce thermalization losses, photon splitting is proposed and observed for a variety of lanthanide-doped materials. For
Er3+, even a one-to-three photon-splitting process has been reported, yielding three IR photons at around 1530 nm following absorption of one blue-green photon. This is especially beneficial for narrow band gap solar cells, such as crystalline
Ge. Here, we report on photon splitting for
Er3+ in
YVO4. Following absorption in the
2H11/2 and
4S3/2 levels (520--550 nm), efficient cross-relaxation (CR) yields two excited
Er3+ ions: one in the
4I9/2 state and one in the
4I13/2 state (CR1). A second CR step from the
4I9/2 state, leaving both
Er3+ ions in the
4I13/2 excited state (CR2), is crucial in realizing efficient three IR photon splitting. It is demonstrated here that the second step has a low efficiency, as a result of competing fast multiphonon relaxation, ${}^{4}{\mathrm{I}}_{9/2}{\ensuremath{\rightarrow}}^{4}{\mathrm{I}}_{11/2}$, and a large energy mismatch, which makes the CR2 step thermally activated. Based on experiments and theory, a maximum quantum efficiency of 170% is calculated for IR emission, following blue-green excitation in
YVO4:Er3+. An outlook is presented for three-photon splitting in low-phonon-energy hosts, where nonradiative multiphonon relaxation is suppressed. The anti-Stokes nature of the second CR step makes three-photon splitting unlikely and prevents the realization of IR quantum yields above 200%.
Optical dephasing of Pr3+ and Tm3+ ions doped in transparent oxyfluoride glass ceramics was studied with the two-pulse photon echo technique. It was found that the dephasing time of rare earth ions is dramatically less in nanocrystals embedded in a glass matrix than in bulk crystals. A quasi-linear temperature dependence obtained at low temperatures proved that the long-range interaction of the ions inside the nanocrystals with the two level systems of the glass matrix dominates the optical dephasing. The local thermal effect in glass ceramics containing nanocrystals elevates the local temperature, which results in the reduction of optical dephasing time. For Tm(3+)-doped glass ceramics, the elevation of local temperature induced by the irradiation of excitation laser even quenched the photon echo signals in the experimental study.
High Resolution Image Download MS PowerPoint Slide Spectral conversion of sunlight can enhance solar cell efficiencies by shifting short-wavelength photons to longer wavelengths, where the photovoltaic response is stronger. This can be realized with near 100% energy efficiency by materials capable of quantum cutting . These emit two longer-wavelength photons, following the absorption of one shorter-wavelength photon. Although various quantum-cutting materials have been reported, follow-up research has often disproved initial claims. Here, we demonstrate that photon correlation analysis is a universal strategy to unambiguously identify quantum cutting. We investigate two materials, YPO 4 codoped with Tb 3+ and Yb 3+ and yttrium aluminum garnet (YAG) codoped with Ce 3+ and Yb 3+ . Both are reported to perform quantum cutting via blue light absorption followed by cooperative energy transfer to near-infrared-emitting Yb 3+, but some studies have cast doubts for YAG:Ce 3+,Yb 3+ . Our correlation analysis demonstrates bunched emission for YPO 4:Tb 3+,Yb 3+, confirming quantum cutting. In contrast, YAG:Ce 3+,Yb 3+ shows Poissonian emission statistics, disproving its quantum-cutting capability, despite previous claims.