Upconversion Process Research Articles

Ultrafast Triplet-Singlet Exciton Interconversion in Narrowband Blue Organoboron Emitters Doped with Heavy Chalcogens.

Narrowband emissive organoboron emitters featuring the multi-resonance (MR) effect have now become a critical material component for constructing high-performance organic light-emitting diodes (OLEDs) with pure emission colors. These MR organoboron emitters are capable of exhibiting high-efficiency narrowband thermally activated delayed fluorescence (TADF) by allowing triplet-to-singlet reverse intersystem crossing (RISC). However, RISC involving spin-flip exciton upconversion is generally the rate-limiting step in the overall TADF; hence, a deeper understanding and precise control of the RISC dynamics are ongoing crucial challenges. Here, we introduce the first MR organoboron emitter (CzBSe) doped with a selenium atom, demonstrating a record-high RISC rate exceeding 108 s-1 , which is even higher than its fluorescence radiation rate. Furthermore, the spin-flip upconversion process in CzBSe can be accelerated by factors of ≈20000 and ≈800, compared to those of its oxygen- and sulfur-doped homologs (CzBO and CzBS), respectively. Unlike CzBO and CzBS, the photophysical rate-limiting step in CzBSe is no longer RISC, but the fluorescence radiation process; this behavior is completely different from the conventional time-delaying TADF limited by the slow RISC. Benefitting from its ultrafast exciton spin conversion ability, OLEDs incorporating CzBSe achieved a maximum external electroluminescence quantum efficiency as high as 23.9 %, accompanied by MR-induced blue narrowband emission and significantly alleviated efficiency roll-off features.

High-sensitive thermometry and tunable dual-color luminescence based on effective energy transfer pathways of Er, Tm system

In this paper, the Er3+,Tm3+ co-doped La2Mo2O9 up-conversion luminescence phosphors are synthesized via solid state reaction. The luminescence characteristics and up-conversion processes of La2Mo2O9:Er3+,Tm3+ phosphors under the excitation of 980 and 1550 nm are investigated in detail. Tm3+ as an important energy transfer medium is the key to effectively improve the population of red-emitting energy levels (4F9/2) in the Er3+ sensitized system. Dual-color luminescence of green and red can be successfully achieved by controlling the concentration ratio of Er3+,Tm3+ co-doping under the dual-wavelength excitation. In addition, the optical temperature sensing ability of La2Mo2O9:Er3+,Tm3+ phosphors is analyzed by employing thermally coupled and non-thermally coupled energy levels. The obtained maximum absolute sensitivities are 8.33 × 10−3 K−1 under the 1550 nm excitation for non-thermally coupled energy levels. The La2Mo2O9:Er3+,Tm3+ phosphors with dual-color luminescence and high temperature sensing ability are the promising candidates in the fields of anti-counterfeiting and non-contact temperature sensing.

Yttrium orthovanadates phosphors as up-conversion luminescent markers for gunshot residue identification

In this work, yttrium orthovanadate phosphors doped with Er3+ and Yb3+ (YVO4: Er3+, Yb3+) were synthetized by the combustion method. After a post-synthesis heat treatment (1100 °C for 6 h), samples were highly crystalline, with only the tetragonal zircon phase remaining. Additionally, all samples presented promising down and up conversion properties, exhibiting a strong green luminescence when excited by either UV or IR radiation. The up-conversion process involved the absorption of two-photons, with the intensity of the Er3+ transitions (2H11/2–4I15/2, 4S3/2–4I15/2 and 4F9/2–4I15/2) heightened with the Yb3+ content. The co-doped orthovanadate samples were introduced into 9 mm non-toxic ammunition (NTA) for evaluation as luminescent markers for gunshot residues (GSR). After shots with marked ammunition were fired, these phosphors enabled the visual detection of luminescent GSR (LGSR) on the shooter, firearm and firing place, facilitating an analysis of the simulated crime scene. These residues also presented a chemical signature that enabled their identification as LGSR. Besides, the down and up conversion properties observed in the residues provide an additional security feature for the unequivocal characterization of the LGSR.

Two-photon-pumped amplified spontaneous emission from Ruddlesden-Popper perovskite flakes.

Herein, we report the two-photon pumped amplified spontaneous emission (ASE) in the 2D RPPs flakes at room temperature. We prepared high-quality (BA)2(MA)n-1PbnI3n+1 (n = 1, 2, 3, 4, 5) flakes by mechanical exfoliating from the fabricated crystals. We show that the (BA)2(MA)n-1PbnI3n+1 flakes display a tunable two-photon pumped emission from 527 nm to 680 nm, as n increases from 1 to 5. Furthermore, we demonstrated two-photon pumped ASE from the (BA)2(MA)n-1PbnI3n+1 (n = 3, 4, 5) flakes. The two-photon pumped ASE thresholds of the RPPs are lower than lots of the other semiconductor nanostructures, indicating an excellent performance of the RPPs for two-photon pumped emission. In addition, we investigated the pump-wavelength-dependent two-photon pumped ASE behaviors of the RPPs flakes, which suggest that the near-infrared laser in a wide wavelength range can be converted into visible light by the frequency upconversion process in RPPs. This work has opened new avenues for realizing nonlinearly pumped ASE based on the RPPs, which shows great potential for the applications in wavelength-tunable frequency upconversion.

Integration of 980/808 nm double sensitizers to fabricate the upconversion nanoparticles/NH2-MIL-101(Fe) hybrid photocatalyst toward ofloxacin, tetracycline, and Cr(VI)

Photocatalysis is a promising pathway to treat the water pollution with lots of distinct advantages, therefore, numerous attentions have been focused on developing the robust photocatalyst to achieve the satisfied activity. Unfortunately, the degradation of antibiotics is still not an easy task by photocatalytic technology due to their stability. A novel composite photocatalyst NaYF4:Yb, Tm, Er, 0.5%Nd@NaYF4:20%Nd/NH2-MIL-101(Fe) (TmErNd@Nd(20%)/NMF) is fabricated by doping Nd3+ ions in both core and shell with the confined amount along with Yb3+ ions in the core. The Yb3+ ions and Nd3+ ions absorb the 980 nm and 808 nm NIR light, respectively. The involvement of Nd3+ ions enlarges the NIR light absorbent region, which facilitates the upconversion process resulting in the improved photocatalytic activity. More important, the 808 nm excitation for Nd3+ ions minimizes the overlap with water absorption at 980 nm. The TmErNd@Nd(20%)/NMF exhibits the excellent photoactivity for ofloxacin (OFL), tetracycline (TC), and Cr(VI) ions as compared with other ones in previous literature. Even in the aqueous environment with the mixed OFL and TC, the TmErNd@Nd(20%)/NMF still keeps the original activity. TmErNd@Nd(20%)/NMF presents the excellent stability with almost no variation of crystal phase and morphology after four cycles. The possible photocatalytic mechanism is conjectured according to the photoelectrochemical measurements, active species trapping experiments, and pump power dependence of upconversion emission intensities. The excellent activity of TmErNd@Nd(20%)/NMF is attributed to its strong near-infrared (NIR) light absorption, less overlap with water absorption, and its special core-shell structure.

Dual Triplet Sensitization Strategy for Efficient and Stable Triplet–Triplet Annihilation Upconversion Perovskite Solar Cells

Dual Triplet Sensitization Strategy for Efficient and Stable Triplet–Triplet Annihilation Upconversion Perovskite Solar Cells

White upconversion emission and color tunability of Y2O3:R(R=Yb3+, Er3+, Tm3+) nanophosphors

The Y2O3:R(R = Yb3+, Er3+, Tm3+) nanophosphors were synthesized by a solvothermal method and the temperature dependence of the white upconversion emission was studied using a 975 nm LD. The upconversion emission spectra in 1 mol% Er3+/5 mol% Yb3+/xTm3+ tri-doped Y2O3 nanophosphors were sintered at 1000 °C with x from 0 to 0.5 mol%. The blue emission intensity increases increasing Tm3+ concentration from 0 to 0.5 mol%, because the Tm3+ state can be easily reached due to the 2F7/2 → 2F5/2 transition of Yb3+ near 10,000 cm−1. The Y2O3: Er3+/Yb3+/Tm3+ nanophosphors exhibit upconversion emission from white to green with increasing sintering temperature. The calculated CIE coordinates are located in the white region at a pump power of 700 mW at 1000 °C, and the color coordinates were very similar to the standard white light emission. Their upconversion process was described through energy level diagrams and results of upconversion emission spectra and pump power dependence.

An Optoelectronic thermometer based on microscale infrared-to-visible conversion devices

Thermometric detectors are crucial in evaluating the condition of target objects spanning from environments to the human body. Optical-based thermal sensing tools have received extensive attention, in which the photon upconversion process with low autofluorescence and high tissue penetration depth is considered as a competent method for temperature monitoring, particularly in biomedical fields. Here, we present an optoelectronic thermometer via infrared-to-visible upconversion, accomplished by integrated light receiving and emission devices. Fully fabricated thin-film, microscale devices present temperature-dependent light emission with an intensity change of 1.5% °C−1 and a spectral shift of 0.18 nm °C−1. The sensing mechanism is systematically characterized and ascribed to temperature dependent optoelectronic properties of the semiconductor band structure and the circuit operation condition. Patterned device arrays showcase the capability for spatially resolved temperature mapping. Finally, in vitro and in vivo experiments implemented with integrated fiber-optic sensors demonstrate real-time thermal detection of dynamic human activity and in the deep brain of animals, respectively.

Manipulating the upconversion luminescence of Yb3+/Er3+ doped nanoparticles by the sheet-shaped nanocavity

Rare-earth doped upconversion luminescence is important for display and imaging field due to its narrow band, multicolor, long lifetime and high stability. However, low quantum yield of upconversion energy transfer, weak excited states absorption and slow spontaneous radiation rates lead to weak upconversion luminescence, which may dramatically limit the practical application of upconversion nanoparticles. Here, we report a metal-sheet-shaped plasmonic nanocavity consisting of gold and silver micro-sheets. It is found that the upconversion processes (including quantum yield of energy transfer, excited states absorption and spontaneous radiation rates) were enhanced by strong local electromagnetic field of the plasmonic nanocavity when RE3+ nanoparticles were filled in the plasmonic nanocavity. The significant enhancement of the luminescence and clear directional radiation were observed under 980 nm laser excitation. By adjusting the nanogap distance of the plasmonic nanocavity, we achieved a 75-fold enhancement in 654 nm emission. Benefiting from the plasmonic nanocavity, the upconversion luminescence exhibited a directional emission, which indicates the plasmonic near-field excitation contributed to the luminescence enhancement. These findings provide a candidate for ring light source and bio-imaging application.

Upconversion photoluminescence and radiative properties of Ba2CaWO6: Er3+ phosphors for photonic applications

Trivalent erbium doped Ba2CaWO6 phosphors were synthesized by the solid-state reaction method. Nephelauxetic ratio and bonding parameter were calculated from the absorption spectrum in order to understand the nature of Er3+ ion-ligand bonds in the prepared phosphor samples. The phenomenological Judd-Ofelt (JO) analysis has been implemented to the recorded absorption spectrum of Ba2CaWO6: Er3+ phosphors for evaluating the JO parameters. Under 980 nm laser diode excitation, Ba2CaWO6: Er3+ phosphor exhibits strong green (4S3/2 →4I15/2) and weak red (4F9/2 →4I15/2) upconversion (UC) emissions centered at 566 and 680 nm and an intense downconversion NIR emission at 1.5 μm. The UC process were assessed on the basis of power dependence of upconversion emission intensity. The significant luminescence features observed from the photoluminescence spectra of Ba2CaWO6: Er3+ phosphors that comprise of both up conversion and down conversion luminescence were discussed in detail with the aid of partial energy level diagram. The better values of radiative properties, luminescence features and CIE color coordinates suggest the suitability of Er3+ doped Ba2CaWO6 material for various photonic applications.

Er3+ concentration-dependent microstructural and upconversion luminescence process of transparent perfluoride composite glass

Er3+-doped transparent perfluoride composite glass (PFCG) containing SrF2 crystals was obtained by a one-step method. PFCG was observed to maintain the formation of a single SrF2 crystal phase even when the Er3+ doping concentration was as high as 8 mol%. Importantly, Er3+ was enriched in the crystalline region, which promoted grain growth. This ensures effective emission of upconversion (UC). Interestingly, green and red UC emissions were found to be tunable in the range of 1–6 mol% Er3+ doping, and the UC emission and lifetime started to produce concentration quenching until 6 mol% Er3+ doping. To the best of our knowledge, this is the highest quenching concentration of Er3+ in composite-glass materials. Moreover, the dominant UC process was systematically analyzed at different doping levels. This research is expected to provide ideal candidate materials and appropriate Er3+ concentration doping level guidance in PFCG for the field of UC lasers.

Exciton Up-Conversion by Well-Distributed Carbon Quantum Dots in Luminescent Materials for an Efficient Organic Light-Emitting Diode.

In this work, we proposed an efficient and straightforward up-conversion process to enhance the external quantum efficiency in a red-emission organic light-emitting diode (OLED). The carbon quantum dots in the luminescent materials initiated the up-conversion by doping the (6,6)-phenyl-C61-butyric acid methyl ester (PCBM) in an amount of 0.001 wt. %, and the external quantum efficiency (EQE) increased from approximately 80% to 9.27% without spectrum change. The time-resolved photoluminescence was applied to understand the mechanism of EQE enhancement in the PCBM-doped OLED. Two decay-time constants fit the TRPL. After PCBM doping, the extended PL intensity indicated increased time constants. The time constants increased from 1.06 and 4.02 ns of the reference sample to 3.48 and 11.29 ns of the PCBM-doped material, respectively. The nonradiative energy transfer (NRET) mechanism was proposed responsible for the decay-time enhancement. The excitons in the PCBM, either by excitation or injection, will transfer to the phosphorescent material nonradiatively. As the PCBM has lower energy levels than the luminous material for electrons, the backward exciton transfer is a kind of up-conversion. With the increased amounts of excitons in the luminescent material, the luminescent external quantum efficiency and the decay-time increased. This up-conversion method is not limited to the red-emission OLED; it could also be applied to blue or green emission.

Optical up-conversion-based cross-correlation for characterization of sub-nanosecond terahertz-wave pulses.

Using a nonlinear optical mixing known as a frequency up-conversion process, we demonstrate an optical cross-correlation technique for the detection and characterization of sub-nanosecond (sub-ns) terahertz (THz)-wave pulses. A monochromatic THz-wave pulse from an injection-seeded THz-wave parametric generator (is-TPG) was mixed with a near-infrared (NIR) pump pulse to generate a NIR idler pulse in a trapezoidal-prism-shaped MgO-doped lithium niobate crystal under the noncollinear phase-matching condition. By measuring pump-energy and crystal-length dependencies, we show that the frequency up-conversion of sub-ns THz-wave pulses with and without subsequent parametric amplification can be used for sensitive detection and intensity cross-correlation characterization, respectively. Using this cross-correlation technique, we reveal that the temporal profile of THz-wave pulses from the is-TPG driven by a 351-ps 1064-nm pump laser has slightly-frequency-dependent pulse width in the range of 150-190 ps at full width at half-maximum in the tunable range of 0.95-2.00 THz.

Efficient UV-visible emission enabled by 532 nm CW excitation in an Ho3+-doped ZBLAN fiber.

Rare-earth-doped ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) fibers have evolved to become promising candidates for efficient UV-visible emission because of their low phonon energy and low optical losses, as well as their well-defined absorption bands. We investigate the efficient emission of UV-visible light in a low-concentration (0.1 mol%) Ho3+-doped ZBLAN fiber excited by a 532 nm CW laser. In addition to the direct populating of the thermalized 5F4+5S2 levels by ground-state absorption, the upconversion processes responsible for UV-visible emission from the higher emitting levels, 3P1+3D3, 3K7+5G4, 5G5, and 5F3, of the Ho3+ ions are examined using excited-state absorption. The dependence of UV-visible fluorescence intensity on launched green pump power is experimentally determined, confirming the one-photon and two-photon characters of the observed processes. We theoretically investigate the excitation power dependence of the population density for nine Ho3+ levels based on a rate equation model. This qualitative model has shown a good agreement with the measured power dependence of UV-visible emission. Moreover, the emission cross-sections for blue, green, red, and deep-red light in the visible region are measured using the Füchtbauer-Ladenburg method and corroborated by McCumber theory, and the corresponding gain coefficients are derived. We propose an alternative approach to achieve efficient UV-visible emission in an Ho3+-doped ZBLAN fiber using a cost-effective, high-brightness 532 nm laser.

Microwave-assisted synthesis and upconversion luminescence of NaYF4:Yb, Gd, Er and NaYF4:Yb, Gd, Tm nanorods

Anisotropic rare earth ion (RE3+) doped fluoride upconversion particles are emerging as potential candidate in diverse areas, ranging from biomedical imaging to photonics. Here, we develop a facile strategy to synthesize NaYF4: Yb, Gd, Er, and NaYF4: Yb, Gd, Tm upconversion nanorods via microwave synthesis route by controlling the synthesis time and compared the optical properties similar nanorods prepared via solvothermal technique. With the increase in synthesis time, the phase of the particle found to change from mixed phase to purely hexagonal and morphology of the particles change mixed phase of spherical and rod-shaped particles to completely nanorods for a synthesis time of 60 min. Further, the intrinsically hydrophobic particles changed to hydrophilic by removal of oleic capping via acid treatment and the amine functionalized silica coating. The upconversion luminescence as well as laser power dependent emission properties of the surface modified particles elucidate that surface modification route influence the upconversion luminescence as well as solvent dependent emission properties. Moreover, the laser power dependent studies elucidate that the upconversion process in a multi-photon process.

Considerations in upconversion: A practical guide to sum-frequency generation spectrometer design and implementation.

In this tutorial review, we discuss how the choice of upconversion pulse shape in broadband vibrational sum-frequency generation (SFG) spectrometer design impacts the chemical or physical insights one can obtain from a set of measurements. A time-domain picture of a vibrational coherence being mapped by a second optical field is described and the implications of how this mapping, or upconversion process, takes place are given in the context of several popular and emerging approaches found in the literature. Emphasis is placed on broadband frequency-domain measurements, where the choice of upconversion pulse enhances or limits the information contained in the SFG spectrum. We conclude with an outline for a flexible approach to SFG upconversion using pulse-shaping methods and a simple guide to design and optimize the associated instrumentation.

Upconversion Emission in Tm/Er/Yb Co‐Doped Yttria Stabilized Zirconia Single Crystals

AbstractBlue, green, and red emissions through upconversion and energy transfer processes are investigated as a function of the Tm3+ concentration in Tm/Er/Yb triply doped yttria stabilized zirconia (YSZ) crystals upon excitation at 980 nm. YSZ doped with 0.075–0.250 mol% Tm2O3, 1.50 mol% Er2O3, and 2.00 mol% Yb2O3 are prepared by the optical floating zone method, and confirmed to be in the cubic phase by X‐ray diffraction. The blue emission corresponds to the Tm3+ 1G4→3H6 transition, and is produced through a three‐photon process, whereas the green and red light are emitted through two‐photon processes from the Er3+ 2H11/2→4I15/2 and 4S3/2→4I15/2 transitions for green and the Er3+ 4F9/2→4I15/2 transition for red. However, interactions between the different lanthanide ions is a factor in determining the overall color of these triply doped crystals, and this is not simply a summation of the results from the singly doped systems, so this mechanism of energy transfer is discussed in detail. The CIE color chromaticity coordinates for the present samples under excitation at 980 nm approach (0.39, 0.55), which is in the yellow‐green region.

Enhanced four-wave mixing from multi-resonant silicon dimer-hole membrane metasurfaces

Tailoring optically resonant features in dielectric metasurfaces unveils a robust scheme to control electromagnetic near fields of light and thus to boost the nanoscale nonlinear light–matter interactions. Membrane metasurfaces offer unique possibilities for supporting multipolar resonances and meanwhile maintaining high mode volume for enhancing nonlinear frequency conversion. Here we design a silicon membrane metasurface consisting of dimer airy holes, as a versatile platform for generating four-wave mixing (FWM). We show that such a metasurface exhibits a multi-resonant feature, including a quasi bound state in the continuum (BIC) generated by the collective toroidal dipole mode excited in the designed subdiffractive periodic system. We show that via employing the BIC mode in the short-wave infrared (SWIR), together with other resonant enhanced electric near fields in the near-infrared (NIR) region, simultaneously, one can convert invisible SWIR light to visible light radiation with high efficiency, via FWM. We experimentally demonstrated a significant FWM emission enhancement from our metasurface, which leads to a conversion efficiency of 0.76 × 10−6 using pump and signal beam peak intensities as low as 0.33 GW cm−2 and 0.17 GW cm−2, respectively. Our results open new routes for enhancing nonlinear efficiencies for up-conversion processes.

Ultralarge anti-Stokes lasing through tandem upconversion

Coherent ultraviolet light is important for applications in environmental and life sciences. However, direct ultraviolet lasing is constrained by the fabrication challenge and operation cost. Herein, we present a strategy for the indirect generation of deep-ultraviolet lasing through a tandem upconversion process. A core–shell–shell nanoparticle is developed to achieve deep-ultraviolet emission at 290 nm by excitation in the telecommunication wavelength range at 1550 nm. The ultralarge anti-Stokes shift of 1260 nm (~3.5 eV) stems from a tandem combination of distinct upconversion processes that are integrated into separate layers of the core–shell–shell structure. By incorporating the core–shell–shell nanoparticles as gain media into a toroid microcavity, single-mode lasing at 289.2 nm is realized by pumping at 1550 nm. As various optical components are readily available in the mature telecommunication industry, our findings provide a viable solution for constructing miniaturized short-wavelength lasers that are suitable for device applications.

−808 nm-activated Ca2+ doped up-conversion nanoparticles that release no inducing liver cancer cell (HepG2) apoptosis

A near-infrared (NIR) light-triggered release method for nitric oxide (NO) was developed utilizing core/shell NaYF4: Tm/Yb/Ca@NaGdF4: Nd/Yb up-conversion nanoparticles (UCNPs) bearing a mesoporous silica (mSiO2) shell loaded with the NO donor S-nitroso-N-acetyl-DL-penicillamine (SNAP). To avoid overheating in biological samples, Nd3+ was chosen as a sensitizer, Yb3+ ions as the bridging sensitizer, and Tm3+ ions as UV-emissive activator while co-doping with Ca2+ was done to enhance the luminescence of the activator Tm3+. NO release from SNAP was triggered by an NIR-UV up-conversion process, initiated by 808 nm light absorbed by the Nd3+ ions. NO release was confirmed by the Griess method. Under 808 nm irradiation, the viability of the liver cancer cell line HepG2 significantly decreased with increasing UCNPs@mSiO2-SNAP concentration. For a UCNPs@mSiO2-SNAP concentration of 200 μg ml−1, the cell survival probability was 47%. These results demonstrate that UCNPs@mSiO2-SNAP can induce the release of apoptosis-inducing NO by NIR irradiation.