Energy Transfer Upconversion Research Articles

Ligand-Sensitized Near-Infrared to Visible Linear Light Upconversion in a Discrete Molecular Erbium Complex.

While the low-absorption cross section of lanthanide-based upconversion systems, in which the trivalent lanthanides (Ln3+) are responsible for converting low- to high-energy photons, has restricted their application to intense incident light, the emergence of a cascade sensitization through an organic dye antenna capable of broadly harvesting near-infrared (NIR) light in upconversion nanoparticles opened new horizons in the field. With the aim of pushing molecular upconversion within the range of practical applications, we show herein how the incorporation of an NIR organic dye antenna into the ligand scaffold of a mononuclear erbium coordination complex boosts the upconversion brightness of the molecule to such an extent that a low-power (0.7 W·cm-2) NIR laser excitation of [L6Er(hfa)3]+ (hfa = hexafluoroacetylacetonate) at 801 nm results in a measurable visible upconverted signal in a dilute solution (5 × 10-4 M) at room temperature. Connecting the NIR dye antenna to the Er3+ activator in a single discrete molecule cures the inherent low-efficient metal-based excited-state absorption mechanism with a powerful indirect sensitization via an energy transfer upconversion, which drastically improves the molecular-based upconverted Er3+-centered visible emission.

Upconversion luminescence and energy transfer in the fluorophosphate glasses with low phosphate content doped with Tm3+ and Yb3+ions

We report an experimental observation of the upconversion in fluorophosphate glasses doped with different concentrations of Tm 3+ ions (from 10 20 to 10 15 ion/cm 3 ) and a constant content of Yb 3+ ions (10 21 ion/cm 3 ) when pumped by a diode laser with a wavelength of 975 nm with a change in the pumping power density from 2.0 to 14.5 kW/cm 2 . Possible mechanisms of population of the upper 1 D 2 , 2 G 4 and 3 F 2,3 states of Tm 3+ ions were discussed depending on their concentration. The role of cross-relaxation processes in the population of the upper excited levels is considered. A change in the values of n -parameter of the luminescence at 475 nm ( 1 G 4 ) from 3 to 2 and high upconversion at low Tm 3+ ions concentrations (about 10 18 -10 15 ion/cm 3 ) were attributed to the cooperative energy transfer from Yb-Yb* dimers. It was found that Tm 3+ /Yb 3+ co-doped fluorophosphate glasses could be promising as up-converting materials. • The concentration dependence of the UC luminescence of Tm 3+ /Yb 3+ co-doped fluorophosphate glasses was studied. • Mechanisms of population of the state 2 D 1, 3 F 2,3 , 1 G 4 and 1 P 0 of Tm 3 + ions were discussed depending on their concentration. • The cooperative energy transfer from Yb-Yb* dimmers led to the high upconversion at low Tm 3+ ions concentrations.

Colloidal upconversion nanocrystals enable low-temperature-grown GaAs photoconductive switch operating at λ = 1.55 μm

Microwave photoconductive switches, allowing an optical control on the magnitude and phase of the microwave signals to be transmitted, are important components for many optoelectronic applications. In recent years, there are significant demands to develop photoconductive switches functional in the short-wave-infrared spectrum window (e.g. λ = 1.3–1.55 μm) but most state-of-the-art semiconductors for photoconductive switches cannot achieve this goal. In this work, we propose a novel approach, by the use of solution-processed colloidal upconversion nanocrystals deposited directly onto low-temperature-grown gallium arsenide (LT-GaAs), to achieve microwave photoconductive switches functional at λ = 1.55 μm illumination. Hybrid upconversion Er3+-doped NaYF4 nanocrystal/LT-GaAs photoconductive switch was fabricated. Under a continuous wave λ = 1.55 μm laser illumination (power density ∼ 12.9 mW μm−2), thanks to the upconversion energy transfer from the nanocrystals, a more than 2-fold larger value in decibel was measured for the ON/OFF ratio on the hybrid nanocrystal/LT-GaAs device by comparison to the control device without upconversion nanoparticles. A maximum ON/OFF ratio reaching 20.6 dB was measured on the nanocrystal/LT-GaAs hybrid device at an input signal frequency of 20 MHz.

Steering Triplet-Triplet Annihilation Upconversion through Enantioselective Self-Assembly in a Supramolecular Gel.

Research on chiral selection and recognition not only is of fundamental importance in resolving the origin of biological homochirality, but also is instructive in the fabrication of controlled molecular organization in supramolecular systems to modulate their chirality-related functional properties. Here we report an enantioselective assembly process between a chiral energy donor and two enantiomeric energy acceptors, which further results in chirality-controlled energy transfer and enantioselective triplet-triplet annihilation upconversion (TTA-UC). It is found that the chiral energy donor Pd(II) octaethylporphyrin derivative PdOEP-LG12 (RD) can selectively coassemble with the chiral energy acceptor LGAn (RA) with the same chiral scaffold but tends to form segregation with the energy acceptor DGAn (SA) with the opposite chiral scaffold in a thermodynamic equilibrium state. Thus, the coassembly of RA/RD shows more effective triplet-triplet energy transfer (TTET) and stronger upconverted luminescence and upconverted circularly polarized luminescence in comparison to the segregation of SA/RD. The establishment of such an enantioselective TTA-UC system highlights the applications of chirality-regulated triplet fusion in optoelectronic materials.

Enantiospecific Detection of D‐Amino Acid through Synergistic Upconversion Energy Transfer

AbstractD‐amino acids (DAAs) are indispensable in regulating diverse metabolic pathways. Selective and sensitive detection of DAAs is crucial for understanding the complexity of metabolic processes and managing associated diseases. However, current DAA detection strategies mainly rely on bulky instrumentation or electrochemical probes, limiting their cellular and animal applications. Here we report an enzyme‐coupled nanoprobe that can detect enantiospecific DAAs through synergistic energy transfer. This nanoprobe offers near‐infrared upconversion capability, a wide dynamic detection range, and a detection limit of 2.2 μM, providing a versatile platform for in vivo noninvasive detection of DAAs with high enantioselectivity. These results potentially allow real‐time monitoring of biomolecular handedness in living animals, as well as developing antipsychotic treatment strategies.

Enantiospecific Detection of D-Amino Acid through Synergistic Upconversion Energy Transfer.

D-amino acids (DAAs) are indispensable in regulating diverse metabolic pathways. Selective and sensitive detection of DAAs is crucial for understanding the complexity of metabolic processes and managing associated diseases. However, current DAA detection strategies mainly rely on bulky instrumentation or electrochemical probes, limiting their cellular and animal applications. Here we report an enzyme-coupled nanoprobe that can detect enantiospecific DAAs through synergistic energy transfer. This nanoprobe offers near-infrared upconversion capability, a wide dynamic detection range, and a detection limit of 2.2 μM, providing a versatile platform for in vivo noninvasive detection of DAAs with high enantioselectivity. These results potentially allow real-time monitoring of biomolecular handedness in living animals, as well as developing antipsychotic treatment strategies.

Molecular light-upconversion: we have had a problem! When excited state absorption (ESA) overcomes energy transfer upconversion (ETU) in Cr(III)/Er(III) complexes

Molecular light-upconversion: we have had a problem! When excited state absorption (ESA) overcomes energy transfer upconversion (ETU) in Cr(III)/Er(III) complexes

Ultrashort pulsed laser amplifier: simultaneous optimization of thermally induced diffraction loss and energy transfer upconversion

In this work, thermally induced diffraction loss and energy transfer upconversion (ETU) are considered for optimization of an ultrashort-pulsed laser amplifier. In this regard, pump spot size and signal to pump mode ratio are optimized in order to maximize the signal output energy. Toward this, the Frantz-Nodvik equation of ultrashort-pulsed laser amplifier with thermal induced diffraction loss and ETU theories were combined. Results show the power of this two-theory combination for optimization tasks of pico-second pulsed amplifiers. Optimized values of m and for output energy of 2.3 µj are reported here. This output energy is twice the values reported without parameter optimization.

Enhanced dual mode luminescence via energy transfer in Er3+, Yb3+ co-doped β-spodumene

Fundamental understanding of the Stokes and anti-Stokes emissions in luminescence materials and their mechanism is very important for different technological applications. In this article, we report the dual mode, down/upconversion (DC/UC), luminescence in a LiAlSi2O6 (β-spodumene) single host along with its mechanistic investigations. A series of emission tunable Li1-xAlSi2O6:xEr3+ (LAS:xEr3+; 0 ≤ x ≤ 0.07) and Li0.99-yAlSi2O6:0.01Er3+,yYb3+ (LAS:0.01Er3+,yYb3+; 0.001 ≤ y ≤ 0.007) phosphor powders were prepared by solid state reaction method at 1300 °C. The formation of single-phase phosphors is verified by XRD technique and other structural properties are investigated by FT-IR, UV-Vis-NIR spectra. The phosphors produced NIR DC emission at 1535 nm (under 380 and 980 nm excitation) and an intense red UC emission at 655 nm (under both 980 and 808 nm excitations). The dual mode emission intensity of the LAS:0.01Er3+ is further improved by co-doping Yb3+ ions via energy transfer from Yb3+ to Er3+. The red UC emission intensity of LAS:0.01Er3+,0.005Yb3+ phosphor under 980 nm excitation is ~10 times stronger than the singly doped LAS:0.01Er3+ phosphor. In addition, the phosphors can also be efficiently excited by 808 nm laser and hence can be used for biological application since 808 nm NIR irradiation exhibits higher light penetration depth without inducing overheating. The mechanism of energy transfer from Yb3+ to Er3+ by considering different emission pathways viz: ground state absorption (GSA), excited state absorption (ESA), energy transfer upconversion (ETU), back energy transfer (BET) and cross relaxation (CR) are discussed in detail. Based on the dual mode emissions, the LAS:xEr3+ and LAS: xEr3+,yYb3+ (x = 0.1 and 0.001 ≤ y ≤ 0.007) phosphors could be a potential candidate not only for the biological application as bio-probe but also as energy convertors for solid-state lighting, displays, and solar cell applications.

Unraveling the Luminescence Quenching of Phosphors under High-Power-Density Excitation

Laser-driven phosphor-converted white light sources have received great attention for next-generation high-brightness lighting and display technologies. However, luminescence quenching of down-conversion phosphors under high-power-density excitation severely restricts the luminous efficacy and light output of laser-driven lighting devices. Till now, the quenching mechanism, once assigned to thermal quenching, is still argued, making it difficult to select appropriate laser phosphors. In this work, we identify the optical excitation quenching (a non-thermal quenching effect) rather than thermal quenching that dominates the luminescence loss of Ce3+- and Eu2+-doped phosphors under high-power-density excitation. The optical excitation quenching is mainly caused by the energy-transfer upconversion (ETU), and the quenching rate is greatly dependent on the decay time of phosphors, evidenced by combining the experimental data with theoretical models. A critical parameter, named as optical excitation quenching behavior, is finally proposed to screen laser phosphors.

Visible-light-driven lanthanide-organic-frameworks modified TiO2 photocatalysts utilizing up-conversion effect

Highly efficient and quite stable composite with core-shell-like architecture reported herein, responds to the challenge of sunlight-driven photocatalysts. The Ln(ndc)/TiO2 photocatalytic system comprises active lanthanide-carboxylate coordination networks (Nd, Er, Ho, and Tm as metal ions, and 2,6-naphthalene dicarboxylic acid as the organic linker) and inert titanium dioxide and allow to convert incompatible visible radiation into functional ultraviolet photons. The combination of the antenna-reactor photocatalyst complex with Ln(ndc) shell layers promotes light harvesting and efficient mass transfer, resulting in additional photoexcited electrons. The Nd(ndc) metal-organic framework successfully activate TiO2via up-conversion energy transfer. The apparent quantum efficiency, determined at wavelengths corresponding to the transitions from the Nd3+ ground state, equals to 2.8% and 3.2% for 525 and 583 nm, respectively. Integration of the Nd(ndc) MOF and TiO2 results in the highest efficiency of phenol degradation, affording a value of 87.5% after 60 min of visible light (λ > 420 nm) exposure.

Luminescence and up-conversion of single crystalline Lu3Al5O12:Pr3+

This work deals with the spectroscopic properties of praseodymium doped single crystalline lutetium aluminum garnet (LuAG:Pr3+). A special focus was set on temperature- and time-dependent spectroscopy. Beyond the well-known down-conversion luminescence of LuAG:Pr3+, also UV-A/B up-conversion luminescence under excitation with a 488 nm laser was thoroughly investigated. Furthermore, the results of the spectroscopic investigations on the single crystalline material were supplemented and compared with measurements on a microscale powder sample.In addition, to the spectroscopic investigations, mechanistic considerations are presented to obtain a closer look at the up-conversion process in LuAG:Pr3+. We promote the thesis of a temperature-dependent energy transfer up-conversion mechanism.

Upconversion Luminescence of Silica-Calcia Nanoparticles Co-doped with Tm3+ and Yb3+ Ions.

Looking for upconverting biocompatible nanoparticles, we have prepared by the sol–gel method, silica–calcia glass nanopowders doped with different concentration of Tm3+ and Yb3+ ions (Tm3+ from 0.15 mol% up to 0.5 mol% and Yb3+ from 1 mol% up to 4 mol%) and characterized their structure, morphology, and optical properties. X-ray diffraction patterns indicated an amorphous phase of the silica-based glass with partial crystallization of samples with a higher content of lanthanides ions. Transmission electron microscopy images showed that the average size of particles decreased with increasing lanthanides content. The upconversion (UC) emission spectra and fluorescence lifetimes were registered under near infrared excitation (980 nm) at room temperature to study the energy transfer between Yb3+ and Tm3+ at various active ions concentrations. Characteristic emission bands of Tm3+ ions in the range of 350 nm to 850 nm were observed. To understand the mechanism of Yb3+–Tm3+ UC energy transfer in the SiO2–CaO powders, the kinetics of luminescence decays were studied.

Spectroscopy and Near-Infrared to Visible Upconversion of Er3+ Ions in Aluminosilicate Glasses Manufactured with Controlled Optical Transmission

In this work we report on the spectroscopic properties and the near-infrared to visible upconversion of Er3+ ions in aluminosilicate glasses manufactured by directionally solidification with the laser floating zone technique. Glasses were manufactured in a controlled oxidizing atmosphere to provide them with high optical transmission in the visible spectral range. Absorption and emission spectra, and lifetimes were assessed in both the visible and the near infrared spectral range. Green upconversion emissions of the 2H11/2→4I15/2 and 4S3/2→4I15/2 transitions at 525 nm and 550 nm attributed to a two-photon process were observed under excitation at 800 nm. Mechanisms responsible for the upconversion luminescence were discussed in terms of excited state absorption and energy transfer upconversion processes. Excitation spectra of the upconverted emission suggest that energy transfer upconversion processes are responsible for the green upconversion luminescence.

Highly efficient 2.3 µm thulium lasers based on a high-phonon-energy crystal: evidence of vibronic-assisted emissions

We report on highly efficient and power-scalable laser operation in a thulium-doped high-phonon-energy crystal [monoclinic double tungstate, K L u ( W O 4 ) 2 ] on the 3 H 4 → 3 H 5 T m 3 + transition giving rise to the short-wave infrared emission at ∼ 2.3 µ m . A 3 at. % Tm-doped crystal generated a maximum continuous-wave output power of 1.12 W at ∼ 2.22 and 2.29 µm with a record-high slope efficiency of 69.2% (versus the absorbed pump power), a slightly multimode beam ( M x , y 2 = 2.2 and 2.6), and a linear laser polarization. The ∼ 2.3 µ m laser outperformed the one operating on the conventional 3 F 4 → 3 H 6 transition (at ∼ 1.95 µ m ). The effect of the Tm concentration on the ∼ 2.3 µ m laser performance indicates a gradually increasing pump quantum efficiency for the 3 H 4 upper laser level with the Tm doping. For the 3 at. % Tm-doped crystal, it reached 1.8 ± 0.1 (almost two-for-one pump process), which is attributed to efficient energy-transfer upconversion. We discuss the physical nature of the laser emissions occurring at intermediate wavelengths between the electronic 3 H 4 → 3 H 5 and 3 F 4 → 3 H 6 transitions and highlight the role of electron-phonon coupling (vibronic processes) in the appearance of such laser lines. This allowed us to better understand the near- and mid-infrared emission from thulium ions, which can be used in broadly tunable and fs mode-locked 2–2.3 µm lasers.

Molecular light-upconversion: we have had a problem! When excited state absorption (ESA) overcomes energy transfer upconversion (ETU) in Cr(III)/Er(III) complexes.

Nine-coordinate [ErN9] or [ErN3O6] chromophores found in triple helical [Er(L)3]3+ complexes (L corresponds to 2,2′,6′,2′′-terpyridine (tpy), 2,6-(bisbenzimidazol-2-yl)pyridine (bzimpy), 2,6-diethylcarboxypyridine (dpa-ester) or 2,6-diethylcarboxamidopyridine (dpa-diamide) derivatives), [Er(dpa)3]3− (dpa is the 2,6-dipicolinate dianion) and [GaErGa(bpb-bzimpy)3]9+ (bpb-bzimpy is 2,6-bis((pyridin-2-benzimidazol-5-yl)methyl-(benzimidazol-2-yl))pyridine) exhibit NIR (excitation at 801 nm) into visible (emission at 542 nm) linear light upconversion processes in acetonitrile at room temperature. The associated quantum yields 5.5(6) × 10−11 ≤ ϕuptot(ESA) ≤ 1.7(2) × 10−9 appear to be 1–3 orders of magnitude larger than those predicted by the accepted single-center excited-state absorption mechanism (ESA). Switching to the alternative energy transfer upconversion mechanism (ETU), which operates in multi-centers [CrErCr(bpb-bzimpy)3]9+, leads to an improved quantum yield of ϕuptot(ETU) = 5.8(6) × 10−8, but also to an even larger discrepancy by 4–6 orders of magnitude when compared with theoretical models. All photophysical studies point to Er(4I13/2) as being the only available ‘long-lived’ (1.8 ≤ τ ≤ 6.3 μs) and emissive excited state, which works as an intermediate relay for absorbing the second photon, but with an unexpected large cross-section for an intrashell 4f → 4f electronic transition. With this in mind, the ETU mechanism, thought to optimize upconversion via intermetallic Cr → Er communication in [CrErCr(bpb-bzimpy)3]9+, is indeed not crucial and the boosted associated upconversion quantum yield is indebted to the dominant contribution of the single-center erbium ESA process. This curious phenomenon is responsible for the successful implementation of light upconversion in molecular coordination complexes under reasonable light power intensities, which paves the way for applications in medicine and biology. Its origin could be linked with the presence of metal–ligand bonding.

Influence of upconversion transition process on the performance of inband pumped holmium-doped silica fiber amplifiers

In this report, a theoretical model of in-band pumped holmium-doped silica fiber amplifiers (HDFAs) is presented. This model is developed to consider the influence of energy transfer up-conversion (ETU) on the HDFAs performance. The advantage of this model is to investigate the properties of HDFAs as a function of holmium-doped fiber length and doping concentration. A good agreement is observed between the simulation results and the previous experimental findings. Our simulation results show the negative impact of ETU process to deteriorate the HDFAs performance and this process may have bigger effect at high holmium doped concentration. This is the first time to our knowledge that the influence of upconversion process is theoretically investigated on the performance of in-band pumped HDFAs.

Simulation and experimental results of a high-gain two-stage and double-pass off-axis Nd:YVO4 picosecond laser amplifier.

A high-gain two-stage double-pass off-axis Nd:YVO4 picosecond laser amplifier has been developed. The comprehensive influence of crystal doping concentration and pump beam quality on the small-signal gain of the Nd:YVO4 amplifier is theoretically analyzed with a model developed by considering energy transfer upconversion and pump light absorption saturation effect. The thermal effect of Nd:YVO4 crystal with different doping concentrations, undoped end cap lengths, and pump beam quality is investigated as well. Based on the theoretical analysis, a high-gain two-stage and double-pass off-axis Nd:YVO4 amplifier based on picosecond fiber seed source is realized by choosing long-composite low-doping Nd:YVO4 crystal and with high brightness laser diode pumping, delivering a gain of 28 dB and an output pulse energy of 67.5 µJ at a repetition rate of 200 kHz.

Erbium-ytterbium co-doped aluminum oxide thin films: Co-sputtering deposition, photoluminescence, luminescent lifetime, energy transfer and quenching fraction

Abstract Erbium-ytterbium co-doped aluminium oxide (Al2O3:Er3+:Yb3+) thin films were deposited on thermally oxidized silicon wafers using reactive radio frequency co-sputtering deposition. The effects of deposition parameters (including oxygen flow rate, substrate temperature and substrate bias) were investigated to obtain low loss Al2O3 films (~0.15 dB/cm at 1550 nm). A set of singly- and co-doped Al2O3 films (surface roughness: ~144.8 p.m.) with various Er3+ concentrations (1.4, 2.0 and 2.5 × 1020 cm−3) and/or Yb3+ concentrations (1.3, 2.1, 3.2, 4.3 and 5.8 × 1020 cm−3) were deposited and investigated. The Er3+ photoluminescence (PL) spectrum around 1550 nm exhibits a pump power-independent full width at half maximum (FWHM) of ~40 nm with and without the presence of Yb3+ as a sensitizer. The luminescent lifetime of Er3+ (4I13/2, 6.52–7.14 m s) exhibits a power-dependent characteristic, while that of Yb3+ (2I5/2, 0.514–0.716 m s) is power-independent. A power-dependent role of energy transfer upconversion is concluded from both the power-dependent Er3+ PL intensity trend and its power-dependent PL decay rate. Yb3+-Er3+ ion energy transfer also exhibits power-dependent characteristics. The energy transfer coefficient (up to ~3.2 × 10−17 cm3s−1) and energy transfer efficiency (up to ~80%) depend on the Yb3+ and Er3+ concentrations. The PL intensity trend and power-dependent absorption of Er3+ and Er3+-Yb3+ under 1469-nm excitation can be well described by using a three-energy-level model. The derived Er3+ quenching fraction based on the fittings of the measured absorption and PL intensity, decreases with the presence of Yb3+ ions. In addition, the Yb3+ quenching fraction was derived based on a two-energy-level model for 973-nm absorption. This work provides parametric references and insights regarding deposition, characterization, and design of the evolving rare-earth-doped Al2O3 platform for on-chip near-infrared applications.

Near-infrared light-mediated Er3+ and Yb3+ co-doped CaTi4O9 for optical temperature sensing behavior

In present report, CaTi4O9: 1 at% Er3+, 1 at% Yb3+ phosphors have been synthesized via sol-gel method and reported herein for its temperature sensing performance. XRD spectra confirms high crystallinity and successful inclusion of rare earth (RE) ions into CaTi4O9 as the dopant ions do no induce any change in the peak position. The X-ray diffraction analysis indicates that the host calcium titanate exhibits hexagonal crystal structure. The green up-conversion (UC) emission observed using 980 nm diode laser excitation. Since, Er3+ ion has ladder type energy levels, thereby it receives energy from Yb3+ ion by excited state absorption and energy-transfer up-conversion processes. Furthermore, the Er3+ ion has two temperature sensing levels 4S3/2→4I15/2 (550 nm) and 2H11/2→4I15/2 (525 nm). Therefore, temperature dependent up-conversion spectra illustrate good temperature sensitivity for present phosphor. The sensitivity of above mentioned phosphor has been evaluated with temperature from 300K to 500K, which shows the suitability of the phosphor for developments in temperature thermometry.