Upconversion luminescence (UCL) of lanthanide-doped nanomaterials is usually a low-efficiency nonlinear process, involving multi-step, multi-channel transitions in a multi-level system. Here, we demonstrate quantum control and enhancement of multi-color (e.g., red and green) UCLs of NaYF4:Yb3+/Er3+ nanoparticles with metallic Fabry-Perot micro-cavities. Besides realization of controlled single-color UCLs, their internal quantum efficiencies are strongly enhanced, up to 3–4 orders of times. Experimental results indicate that the controlled single-color UCLs and enhancements are caused not only by modifications of the spontaneous radiation rates for the red- and green-color transitions but also by influencing the intermediate transitions to result in modified distributions of electrons in each of the multiple Er3+ levels, facilitating emission of either red- or green-color light. This work suggests a way to control photon emissions in systems with multi-channel transitions and/or multi-step excitations.
Upconversion luminescence (UCL) of lanthanide-doped nanomaterials is usually a low-efficiency nonlinear process, involving multi-step, multi-channel transitions in a multi-level system. Here, we demonstrate quantum control and enhancement of multi-color (e.g., red and green) UCLs of NaYF4:Yb3+/Er3+ nanoparticles with metallic Fabry-Perot micro-cavities. Besides realization of controlled single-color UCLs, their internal quantum efficiencies are strongly enhanced, up to 3–4 orders of times. Experimental results indicate that the controlled single-color UCLs and enhancements are caused not only by modifications of the spontaneous radiation rates for the red- and green-color transitions but also by influencing the intermediate transitions to result in modified distributions of electrons in each of the multiple Er3+ levels, facilitating emission of either red- or green-color light. This work suggests a way to control photon emissions in systems with multi-channel transitions and/or multi-step excitations.
The NV center in diamonds has been widely employed in quantum sensing, quantum computing, and bioimaging due to its controllable ground-state spin, detectable magnetic resonance, excellent photostability, favorable biocompatibility, and chemical inertness. However, conventional excitation using 532 nm green light still exhibits certain limitations in practical applications. To address this, we propose a novel NV center excitation method based on the upconversion of near-infrared light to green emission. Through the synthesis of molybdenum-doped NaYF4: 20% Yb3+, 1.5% Er3+ upconversion materials, efficient excitation of NV centers has been achieved. Both UC-LED luminescence spectroscopy and ODMR measurements confirm that the green light generated via the upconversion process exhibits sufficient intensity to effectively excite NV centers. Meanwhile, the characteristic sharp emission peaks of rare-earth upconversion materials eliminate the need for optical filters, facilitating device miniaturization, and a miniaturized UC-LED sensor has been developed.
The enhancement and tunable color emissions from codoped lanthanide ions of Er3+/Tm3+/Yb3+ have been studied extensively in recent decades. In this paper, we present a new scheme for quantum coherent control of two-photon absorption (TPA) and color emission in codoped lanthanide ions of Er3+/Tm3+/Yb3+ by properly phase shaping two infrared ultrashort laser beams at central frequencies of 10 650 cm−1 and 7650 cm−1, respectively. Compared with the results irradiated by transform-limited pulses, the TPA probabilities of the blue, green and red emissions are independently controlled in the ranges 0–13.3, 0–14.5 and 0–1.0, respectively. The effects of the energy states of lanthanide ions and the laser spectral bandwidths on the coherent features are also discussed. The TPA probabilities for the blue and green emissions increase with the laser spectral bandwidths and decrease with the energy bandwidths of the final level states. As the intermediate energy level shifts in the range 10 100–10 500 cm−1, the TPA probabilities for the blue and green emissions change in the ranges 7–15 and 8–17, respectively.
Abstract Photon upconversion through lanthanide-doped nanoparticles is of great significance for various applications. However, the current development of upconversion nanoparticles is hindered by the low quantum efficiency and long radiative lifetimes of lanthanide ions, restricting their applications in time-dependent nanophotonics. Herein, we report ultrafast upconversion superfluorescence with a lifetime of sub-2.5 ns in lanthanide-doped nanoparticles at room temperature. Upon excitation with an 800-nm fs-pulsed laser, we achieve a large number ( N = 912) of correlated dipoles in Nd 3+ -concentrated nanoparticles, resulting in collective coherent emission with two orders of magnitude amplification in intensity and more than three orders of magnitude improvement in the radiative decay rate. Furthermore, we demonstrate that the control of excitation power and emitting sample length enables the lifetime manipulation of upconversion emission in a wide range from μs to sub-ns, accompanied by the typical superfluorescence signature of Burnham-Chiao ringing. These findings may benefit applications in many advanced technologies such as quantum counting and high-speed super-resolution bioimaging.
Fundamental studies of light-matter interactions are important for basic knowledge and in applications. Thanks to advances in experimental and theoretical methods, nowadays it is possible to perform such studies in a broad dynamic range, covering timescales from that of elementary interactions to real time. In the present work, we perform an experimental-theoretical study of light intensity-dependent femtosecond and CW-laser induced frequency upconversion in hierarchically structured core-multishell nanoparticles co-doped with NdIII, YbIII, and ErIII. Upconversion spectra recorded with CW and femtosecond excitation are qualitatively similar whereas the intensity dependence of upconversion depends on excitation mode (CW or femtosecond). To further assess the observed intensity dependence, we perform light-matter interaction simulations in the dynamic range from 100 fs to 3 ms for 18-level system describing the UCNPs, including 9 NdIII levels, 2 YbIII, and 7 ErIII levels and a classical model for the excitation source. The calculated time- and intensity-dependent energy level population are compared with measured spectra to understand CW vs femtosecond laser-induced upconversion. To further discuss the differences between CW and femtosecond laser-induced light-matter interactions for the systems studied here, we perform semi-classical pulse propagation simulations and ultrafast pump-probe measurements to study how the light source bandwidth, relative to the absorption linewidth, influence light absorption and transmission and further connect these results with the intensity dependence. Overall, we report our progress toward mechanistic studies of light-matter interaction and photophysical pathways following femtosecond excitation and UCNPs.
Abstract Superfluorescence (SF), a collective quantum phenomenon originating from correlated emitters, has historically required cryogenic temperatures or magnetic fields and been limited to narrowband Stokes-shifted emission. Although room-temperature SF has recently been realized in lanthanide-doped systems, active control over its spectral properties remains significant challenges. Here, we propose a state-entropy framework to reveal the coherence evolution and macroscopic dipole correlation in upconversion systems, providing a theoretical foundation for manipulating superradiant processes across a broad spectral range. Based on this framework, we designed an excitation strategy to decouple and regulate the distinct energy-population pathways, specifically excited-state absorption and energy transfer upconversion/cross-relaxation, in ~23 nm NaNdF₄ nanocrystals at room temperature. This approach enables multi-stage upconversion superfluorescence with tunable oscillations and nanosecond to sub-microsecond lifetimes. Most importantly, it substantially extends the accessible spectral window of room-temperature UC-SF from the previously reported two orange-red bands to six distinct emission bands covering the ultraviolet to the red (384-659 nm), accompanied by a wide-gamut wavelength-synthesized color evolution. Furthermore, cascaded excitation enables real-time emission enhancement by restoring the macroscopic dipoles correlation during the SF decay phase. This work demonstrates principles that may inform future designs of on-chip ultrafast optical computing based on spectrally tunable SF with encodable photonic emission.
The interaction of single quantum emitters with an optical cavity enables the realization of efficient spin-photon interfaces, an essential resource for quantum networks. The dynamical control of the spontaneous emission rate of quantum emitters in cavities has important implications in quantum technologies, e.g., for shaping the emitted photons' waveform or for driving coherently the optical transition while preventing photon emission. Here we demonstrate the dynamical control of the Purcell enhanced emission of a small ensemble of erbium ions doped into a nanoparticle. By embedding the nanoparticles into a fully tunable high finesse fiber based optical microcavity, we demonstrate a median Purcell factor of 15 for the ensemble of ions. We also show that we can dynamically control the Purcell enhanced emission by tuning the cavity on and out of resonance, by controlling its length with sub-nanometer precision on a time scale more than two orders of magnitude faster than the natural lifetime of the erbium ions. This capability opens prospects for the realization of efficient nanoscale quantum interfaces between solid-state spins and single telecom photons with controllable waveform, for non-destructive detection of photonic qubits, and for the realization of quantum gates between rare-earth ion qubits coupled to an optical cavity.