Nonradiative Channels Research Articles

Regulation of internal reorganization energy to change the non-radiative channel in the Ir(iii) complex: the role of N atoms

This study examines the influence of ligands with different N-substitution modes and heavy atom effects on transition metal complexes.

Red fluorescent benzothiadiazole derivative loaded in different nanoformulations: Optical properties and their use in bio-imaging

Fluorophores with optimized nonlinear optical properties have become prominent as contrast labels in laser scanning microscopy (LSM). The purpose of this work is to report on a novel benzothiadiazole derivative, namely 4,7-bis(5-((9,9-dioctyl-9H-fluoren-2-yl)ethynyl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole (EFBT) and its optical performance when it is loaded into organic nanostructures intended as labels for LSM. Four different nanostructured labels were prepared: i) EFBT-loaded silica nanoparticles (SiNPs); ii) folate-bioconjugated SiNPs (SiNPs-FA); iii) EFBT-loaded PEGylated nanoparticles (NPs-PEG); and iv) EFBT-loaded folate-terminated PEGylated nanoparticles (NPs-PEG-FA). All these nanostructures are reported through a comparative study of their linear and nonlinear optical properties, including their performance as exogenous label agents in the cervical cancer cell line HeLa. This assessment of the performance of a specific fluorophore loaded into different nanostructured matrices (labels), and fairly compared under the same characterization conditions, including the LSM settings, is less common while previous reports had focused in comparing silica and PEGylated nanoparticles but loaded with different fluorophores. The results show that the internal molecular organization into each type of organic nanostructure impacted differently the properties of EFBT, where the silica matrix tend to preserve the optical performance of the fluorophore by preventing intermolecular interactions; in contrast, PEGylated nanoparticles favored molecular interactions and introduced non-radiative decay channels that degrades drastically the optical performance. Nevertheless, the use of functionalized ends entities produced a better cellular label uptake with PEGylated that with silica nanoparticles. In overall, the NPs-PEG-FA label produced the best HeLa imaging.

Deciphering the mechanism of undoped and heteroatom doped-carbon dots for detection of lead ions at nanomolar level

Herein, two types of facile, simple, and eco-friendly nanosensors were developed for the sensing of Pb2+ ions follow the aggregation-induced emission enhancement (AIEE) and dynamic quenching mechanism. Two types of carbon dots i.e., undoped carbon dots (u-Cdots) and nitrogen, sulfur co-doped carbon dots (N, S-Cdots) were developed by a rapid single-step approach under high-temperature treatment without any solvent. Both the prepared carbon dots showed high water solubility and excellent stability. The particle size of u-Cdots and N, S-Cdots were determined to be 7.5 nm and N, S-Cdots 1.8 nm, respectively which was examined through transmission electron microscope (TEM). The incorporation of heteroatom doping into the N, S-Cdots was examined through X-ray photoelectron spectroscopy (XPS). The u-Cdots shows excitation-dependent PL behaviour whereas, N, S-Cdots shows excitation-independent PL behaviour. Further, both the carbon dots act as sensitive and selective sensing platforms for Pb2+ ions in nanomolar range. Different photophysical investigations (fluorescence quantum yield, average lifetime, and radiative and non-radiative deactivation channels) were thoroughly studied to support the different PL mechanisms. Both the prepared sensing platforms exhibited a good limit of detection (LOD) i.e., 30 nM and 7 nM for u-Cdots and N, S-Cdots, respectively. The developed sensing platforms were also used in real sample analysis for the detection of Pb2+ ions.

The effect of alkoxyl groups on the photoproperties of meta-octasubstituted tetraphenyl porphyrins

• . Installing substituent groups with different lengths/sizes and conformations at the meta-octa-substituted position of meso-tetraphenyl porphyrin. • . H 2 T(OHE) 2 PP with longer and branched alkoxyl chains effectively suppressed aggregation-caused quenching effect. • . H 2 T(OH) 2 PP in solid state shows the naked-eye visible fluorescence, making its practical applications possible. The emission of most organic fluorescent molecules in aggregation states decays or fades, as interpreted by the aggregation-caused quenching (ACQ) effect, because the excited state energy is depleted via nonradiative channels when chromophores stack together. However, most fluorescent materials are utilized in the solid state, and hence it is vital to tune the chromophore stacking mode for modulating the photoluminescence properties. In this work, the meso-tetraphenyl porphyrin was taken as the parent chromophore unit to investigate the substituent-group effect on the luminescence properties of porphyrin-based complexes. The selected substituent groups (-OH, -OMe and 2-ethylhexyloxy) with different lengths/sizes and conformations were installed at the meta-octa-substituted position of meso-tetraphenyl porphyrin. The distance of porphyrin chromophores was regulated by the substituent chain. It was found that in the solid or aggregate state, porphyrin with longer and branched alkoxyl chains effectively suppressed the π-π stacking interaction, maintained the photoluminescence property of the porphyrin chromophore as in its dilute solution and overcame the ACQ effect. In contrast, porphyrin with a shorter alkoxyl chain, for example, the methoxyl group, affords a weak emission property in the solid state, and the substituent hydroxyl group leads to the complete quenching of the emission in the solid-state due to the close stacking of porphyrin rings.

Enhancement of excitonic and defect-related luminescence in neutron transmutation doped β−Ga2O3

Neutron irradiation analysis, inductively coupled plasma mass spectrometry (ICPMS), and cathodoluminescence (CL) spectroscopy are used to investigate the influence of transmuted Ge incorporation on the luminescence properties of $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ single crystals. Calculations based on ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$-neutron interaction reveal temporal variations of both Ge and Zn concentrations as a function of time during and after neutron irradiation. To produce a concentration of $5\ifmmode\times\else\texttimes\fi{}{10}^{18}\phantom{\rule{0.16em}{0ex}}\mathrm{Ge}\phantom{\rule{0.16em}{0ex}}\mathrm{donors}/\mathrm{c}{\mathrm{m}}^{3}$ from the neutron transmutation of Ga, the $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ crystal was irradiated for 27 h, which was accompanied by the incorporation of ${10}^{16}\phantom{\rule{0.16em}{0ex}}\mathrm{Zn}\phantom{\rule{0.16em}{0ex}}\mathrm{acceptors}/\mathrm{c}{\mathrm{m}}^{3}$. These calculated dopant concentrations are confirmed by ICPMS. The $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ crystals exhibit a UV band at 3.40 eV due to self-trapped holes (STHs) and two blue donor-acceptor pair (DAP) peaks at 3.14 eV (BL1) and 2.92 eV (BL2). In addition to the neutron-induced incorporation of substitutional Ge donors and Zn acceptors on Ga sites, Ga vacancies (${V}_{\mathrm{Ga}}$) were created by high-energy neutrons in the flux, which strongly enhanced the BL1 peak. The ${V}_{\mathrm{Ga}}$ acceptors compensate the neutron-induced Ge donors, making the ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ crystal highly resistive. Concurrent temperature-resolved CL measurements of the $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ before and after neutron irradiation reveal a twofold increase in both the STH and BL1 peaks. This result suggests that STHs are preferentially localized at an O site adjacent to ${V}_{\mathrm{Ga}}$, as theoretically predicted by Kananen et al. [Appl. Phys. Lett. 110, 202104 (2017).]. Analysis of the ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ CL temperature dependence reveals that the UV and BL1 bands after the neutron irradiation exhibit an equivalent activation energy of $100\ifmmode\pm\else\textpm\fi{}10\phantom{\rule{0.16em}{0ex}}\mathrm{meV}$ due to the presence of a neutron-induced defect that acts as an efficient competitive nonradiative recombination channel. The results also provide evidence that the BL1 and BL2 bands arise from different DAP pairs.

Collective modulation of upconversion in Ag-BaTiO3: Yb3+, Er3+ by photonic bandgap and surface plasmon resonance effects

A series of Ag-BaTiO3: Yb3+, Er3+ inverse opal structures were synthesized by co-precursor sol-gel method. Under near-infrared excitation, the enhanced upconversion emissions were obtained by the coupling of photonic band gap and surface plasm on resonance effects. The green and red luminescence of Ag-BaTiO3: Yb3+, Er3+ were up to 14.2-fold and 12.8-fold higher than the reference sample, respectively. In addition, a rate equation model has been established based on the energy transfer processes, and a thorough analysis has been conducted to clarify the influence of two effects. By altering the photonic bandgap position, corresponding spontaneous emissions could be inhibited and the efficiency of incident light could be improved. With the introduction of plasmonic structures, the green to red ratio was able to be manipulated by the Purcell factor of radiative decay rate and the additional nonradiative decay channels described by Wnr. This work employs an intriguing strategy for modulating and enhancing upconversion luminescence, which is of great value for potential applications in displays and bio-lables.

Continuous Flow Aqueous Synthesis of Highly Luminescent AgInS2 and AgInS2/ZnS Quantum Dots

Continuous flow synthesis of semiconductor quantum dots (QDs) holds the promise of being highly reproducible, being scalable, and providing precise control of all reaction parameters. Here, we applied this technique to the aqueous synthesis of the Ag–In–S (AIS) core and AIS/ZnS core/shell QDs and optimized several parameters comprising reaction temperature, pressure, time, nature, and the ratio of precursors. Photoluminescence quantum yield (PLQY) values of 32%/44% (average/best) for the core and 77%/83% for the core/shell system have been obtained in short reaction times (8–15 min). We demonstrate by means of combined structural and optical studies that the high PLQY originates from donor–acceptor pair recombination processes, involving essentially [InAg2+ + 2VAg–] defect complexes whose formation is favored by the large excess of indium used (In:Ag ratio of 4:1), and the low reaction temperature (100–120 °C). The structural disorder is further enhanced during ZnS shell growth, which in addition to surface passivation and removal of nonradiative decay channels leads to the partial diffusion of the added zinc ions into the AIS core and the formation of ZnIn− antisite defects. The presented method provides excellent reproducibility and high scalability, facilitating the large-scale production of highly luminescent AIS/ZnS QDs.

Excited-State Dynamics of Proflavine after Intercalation into DNA Duplex

Proflavine is an acridine derivative which was discovered as one of the earliest antibacterial agents, and it has been proven to have potential application to fields such as chemotherapy, photobiology and solar-energy conversion. In particular, it is well known that proflavine can bind to DNA with different modes, and this may open addition photochemical-reaction channels in DNA. Herein, the excited-state dynamics of proflavine after intercalation into DNA duplex is studied using femtosecond time-resolved spectroscopy, and compared with that in solution. It is demonstrated that both fluorescence and the triplet excited-state generation of proflavine were quenched after intercalation into DNA, due to ultrafast non-radiative channels. A static-quenching mechanism was identified for the proflavine-DNA complex, in line with the spectroscopy data, and the excited-state deactivation mechanism was proposed.

Ultrafast excited state relaxation of a model green fluorescent protein chromophore: Femtosecond fluorescence and transient absorption study

The intrinsic excited state properties of green fluorescent protein (GFP) chromophore have inspired syntheses of its structural analogues with a motivation to replicate or improve its excited state properties for biological imaging. In this work, we report torsional-motion mediated multi-coordinate relaxation pathway to explain the excited state dynamics of a GFP chromophore analogue, (4Z)-4-(4-N,N-Dimethylaminobenzylidene)-1,2-diphenyl-1,4-dihydro-5H-imidazolin-5-one (DPI), using femtosecond fluorescence up-conversion, femtosecond transient absorption and quantum chemical calculations. The excited state dynamics of this chromophore involves the formation of an N,N-disubstituted amine twisting mediated intramolecular charge transfer state on a sub-picosecond timescale. This intramolecular charge transfer event prepares an intermediate state that undergoes a “non-volume conserving” twist motion along an exocyclic double bond. The quantum chemical computations further predict that the twist motion along the exocyclic double bond is activated and leads to the formation of a conical intersection between S1 and S0 states of DPI, which is the main nonradiative channel of deactivation. This study confirms that for a structural analogue of GFP chromophore to exhibit excited state properties like the GFP, would require preventing such nonradiative pathways, which can be achieved by restricting the twisting degree of freedom about the exocyclic double bond.

Adsorption-Induced Fluorescence of Pseudoisocyanine Monomers in Systems with Layered Silicates

Interaction of organic dyes with layered silicates can cause various changes in dye properties, such as metachromasia (color change), fluorescence quenching, resonance energy transfer, or even fluorescence enhancement. These phenomena are caused by the molecular aggregation or adsorption of dye molecules on silicate particles. The present work studied the photophysical properties of pseudoisocyanine (PIC) in colloidal dispersions of five samples of layered silicates (smectites) at variable PIC/smectite loadings. The silicates of variable composition and layer charge included one synthetic saponite, one synthetic hectorite, two synthetic Laponites, and one montmorillonite. Chemometric analysis of the absorption spectra revealed the formation of four spectral species: monomers and three types of molecular aggregates exhibiting light absorption in both H- and J-band regions. In addition, the samples of hybrid systems with silicates of lower layer charge under the condition of the lowest PIC/silicate ratio (0.01 mmol g–1) exhibited strong fluorescence surpassing that of J-aggregates. The luminescent species achieving quantum yields of about 50% were assigned to the adsorbed PIC monomers, a phenomenon that has never been observed for this dye. Theoretical calculations found that in water solution bending of the molecule supports nonradiative deactivation of the excited state of the free molecule. Adsorption of PIC molecules on the surface of silicate particles caused the change of the dihedral angle between pyridine subunits, which hinders the nonradiative deactivation channel and favors emission. Fluorescence from adsorbed monomers exhibited a maximum at ≈535 nm, which is at significantly lower wavelengths with respect to the J-aggregates emitting at ≈570 nm and thus cannot be related to dye aggregation as supported by the fact that this phenomenon occurs only at the lowest surface concentrations of the dye.

Compositional variation in Gd2Zr2-xHfxO7:Eu3+ pyrochlore by modulating Zr/Hf ratio and their immediate impact on luminescence properties

Understanding structure-composition-property correlation is very important in optimal design of efficient functional materials. Pyrochlore materials are considered a great exponent for ‘materials for society’ owing to their several multifunctional properties in the area of health, energy and environment. We have synthesized Gd2Zr2-xHfxO7: Eu (0.00 ≤x ≤2.00) and explored it's structural and optical properties using Rietveld refined X-ray diffraction (XRD), time resolved photoluminescence (TRPL) and positron annihilation lifetime spectroscopy (PALS). Emission spectra depicted asymmetric environment around europium ion in all the samples with higher value in solid solution compared to Gd2Zr2O7:Eu3+ (GZOE) and Gd2Hf2O7 (GHOE) which is in line with trend in Judd-Ofelt parameters. XRD measurement has suggested incorporation of Hf4+ into the Gd2Zr2O7 structure leads to strengthening of Gd-O bonds within the structure whereas weakening of Zr/Hf-O bond was observed (try to include Raman spectra also) with creation of more number of smaller vacancy clusters than GHOE and GZOE. Average lifetime consistently increases as we move from GZOE to GHOE wherein Zr4+ are gradually being replaced by Hf4+ sites endowed by more symmetric environment around Eu3+ as Hf4+ content is increased or having GHOE as more ordered system than GZOE. Internal Quantum efficiency (IQY) was found to be higher for solid solution compared to end members GZOE and GHOE. The end members have more sources of non-radiative channels and low asymmetry ratio. We believe this work will give much sought out information in designing lanthanide ion doped pyrochlore for red emitting phosphor for phosphor converted LEDs.

Through-Space Conjugated Supramolecular Polymer Radicals from Spatial Organization of Cucurbit[8]uril: An Efficient Approach for Electron Transfer and Smart Photochromism Materials

Electron transfer-based long-lived radicals are highly challenging because of the limited control over relative orientation, distance, electronic coupling, and nonradiative recombination channels of the donor and acceptor on a molecular level. Herein, the cavity of macrocyclic cucurbit[8]uril (Q[8]) was found to exhibit excellent advantages in controlling the relative orientation and distance of the donor and acceptor moieties via the spatial organization, i.e., the 4-carboxylphenyl appended viologen-derived guest (BcpV2+) was elegantly rearranged as a rigid linear J-type supramolecular polymer by the Q[8] host via noncovalent interactions. Thus, an unprecedented photoinduced electron transfer (PET) triggered through-space conjugated organic radical with distinct photochromism and a NIR-II photothermal effect was observed. Further studies have indicated that the Q[8] encapsulation-triggered PET cycle exhibited good repeatability without significant loss of its efficiency and had potential application in the fabrication of smart windows and erasable printing under photoirradiation or sunlight. These results suggest that the Q[8] host can be used as a new tool in light-energy conversion and photochromism materials science.

A comparative photophysical study on the structurally related coumarin 102 and coumarin 153 dyes

Photophysical properties of two 7-aminocoumarin dyes, namely, coumarin 102 (C102) and coumarin 153 (C153), have been investigated in different aprotic solvents to understand their polarity dependent behaviors. Both the dyes have the same closed-ring amine (julolidyl) substituent at 7-th position of their 1,2-benzopyrone moiety, but differ in regard to their 4-CH3 and 4-CF3 substituents, respectively. For both the dyes, absorption and fluorescence spectra undergo red shift, peak energies of these transitions decrease and the Stokes’ shifts follow linear correlations with the increasing solvent polarity parameter Δf, as defined by Lippert-Mataga. While fluorescence quantum yield (Φf) and lifetime values (τf) of C102 dye undergo linear changes with Δf, both these parameters for C153 display quite unusual deviations from linearity in the lower polarity solvents. For C102, the estimated fluorescence decay rates (kf) are significantly higher than C153 dye. The nonradiative decay rates (knr) are also substantially higher for C102 dye than C153 in most of the solvents. Interestingly, while kf values for both the dyes change linearly with Δf, the knr values show complete linearity with Δf for C102 dye only, but these values for C153 dye show quite substantial enhancements and an unusual positive deviation from linearity in lower polarity solvent. Quantum chemical studies indicate that for C153 dye in lower polarity solvents, especially, there is a possible involvement of intersystem crossing process, which might induce an additional nonradiative channel (kadd-nr) for the dye. Further, though we could not obtain any direct evidence in the present study, yet it is felt that some kind of fluorous effect, as might be arising due to large negative charge density on bulky perfluomethyl group of C153 dye, can also introduce additional kadd-nr, specifically in the nonpolar solvents, for which further investigations are continuing in our group.

Laser‐Induced Secondary Crystallization of CsPbBr3 Perovskite Film for Robust and Low Threshold Amplified Spontaneous Emission

AbstractAll‐inorganic perovskite nanocrystals (NCs) have received extensive attention for next‐generation thin film devices due to their excellent optical properties, such as strong light absorption, high carrier mobility, and defect tolerance. However, significant challenges remain to obtain high‐quality perovskite thin films. Herein, a simple but effective post‐treatment by laser irradiation for CsPbBr3 NCs thin films is reported. Laser‐induced secondary crystallization is observed in CsPbBr3 NCs thin films after treatment. In addition, amplified spontaneous emission (ASE) with a low threshold (5.6 µJ cm−2) and a high gain value (743 cm–1) is achieved. Based on optical measurements, it is attributed to the low defect density, reduced Auger recombination, and weak exciton–phonon interactions, which greatly suppress the nonradiative recombination channels. The ASE from the film after treatment has a high characteristic temperature (134 K), showing a stable optical gain performance that maintains its intensity for 35 h at room temperature (and 12 h at 40 °C). Finally, the proof‐of‐concept demonstration of graphic coding is shown. This study deepens the understanding of the optical gain mechanism of CsPbBr3 perovskite films and provides a simple and convenient laser treatment that enables the fabrication of high‐quality CsPbBr3 perovskite thin films.

Investigation of spatially localized defects in synthetic WS2 monolayers

While the spatially nonhomogeneous light emission from synthetic ${\mathrm{WS}}_{2}$ monolayers is frequently reported in the literature, the nature of this phenomenon still requires thoughtful investigation. Here, we combine several characterization techniques (optical imaging, scanning probe and electron microscopy) along with density functional theory to investigate the presence of substitutional doping localized at narrow regions along the S zigzag edge of ${\mathrm{WS}}_{2}$ monolayers. We verified that photoluminescence quenching along narrow regions is not related to grain boundaries but to substitutional impurities of lighter metals at the W sites, which modify the radiative and nonradiative decay channels. We also found potential candidates for occupying the W site through ADF-STEM analysis and discussed their impact on photoluminescence quenching by performing density functional theory calculations. Our findings shed light on how atomic defects introduced during ${\mathrm{WS}}_{2}$ monolayer's synthesis impact the crystalline quality and, therefore, the development of high-performance optoelectronic devices based on semiconducting 2D materials.

Radiative and Non-Radiative Exciton Recombination Processes in a Chemical Vapor Deposition-Grown MoSe2 Film

In transition metal dichalcogenides (TMDs), defects and stress in thin films significantly affect the dynamic of exciton recombination. Here, we report that a MoSe2 continuous film, grown on a SiO2/Si substrate by chemical vapor deposition (CVD), shows an exceptionally strong photoluminescence (PL) and a rather long lifetime (∼154 ns) at 6 K. However, when the film is transferred to another similar substrate, its PL intensity is remarkably reduced by almost 80. By analyzing temperature-dependent PL and time-resolved PL spectra for the as-grown and transferred films, it reveals that the strong PL of the as-grown MoSe2 sample comes from the exciton recombination from the band tails. We believe that the tensile strain introduced during CVD growth can effectively suppress the non-radiative channels of the excitons in the localized band tails. Our studies demonstrate that the effect of defects and stress on the kinetics of exciton recombination in MoSe2 is of great significance for the application of TMDs in optoelectronics.

Time-resolved terahertz spectroscopy for probing the effects of low-temperature annealing on CsPbBr3 evaporated thin-films

The fine-tuning of the growth conditions and post-deposition treatments is of fundamental importance to improve the efficiency of photovoltaic devices based on all-inorganic metal halide perovskites like CsPbBr3. In this work, we used time-resolved terahertz spectroscopy (TRTS) in combination with optical characterization techniques, x-ray diffraction (XRD), and scanning electron microscopy, to probe the different properties induced by a low-temperature (180 °C) annealing treatment on evaporated CsPbBr3 thin-films. We observed a faster build-up and relaxation dynamics in the annealed sample, accompanied by a remarkable decrease of the photoluminescence intensity and minor changes in the photoconductivity and XRD measurements as compared to the as-deposited sample. We estimated for both the samples a mobility of cm2 V−1 s−1. Our results suggest that the lattice reorganization induced by low-temperature annealing of evaporated CsPbBr3 could lead to a different charge carrier-phonon coupling and to an increased contribution of non-radiative recombination channels. We found that TRTS can be effectively used to follow the changes induced by post-deposition thermal annealing of CsPbBr3.

Excited state processes in nitrile-substituted 2-(oxazolinyl)-phenols in gas and implicit solvents: A computational study

In this work, ground and excited state properties of two nitrile-substituted 2-(oxazolinyl)-phenols in the gas phase, and in two implicit solvents (cyclohexane and methanol) are reported. Computational studies comprising of static calculations at density functional theory (DFT) and ab initio, and non-adiabatic dynamics at DFT levels are performed. The implicit solvent has little influence on the proton transfer (PT) timescale in the S1 state and an average PT time of ∼11–15 fs is predicted. Following PT, non-radiative decay channels are explored and these channels are found to be more probable in the gas and cyclohexane than in methyl alcohol.

Insight into Isomeric Effect on the Photoluminescence and Mechanoluminescence of Cyanostilbene Derivatives.

Molecular structures, packings, and intermolecular interactions significantly affect the photophysical properties of organic luminogens. In this work, the photoluminescence (PL) and mechanoluminescence (ML) of two pairs of isomers, 1/2 and 3/4, were systematically explored. The fluorescence of crystals 1c and 4c is much brighter than that of their isomers 2c and 3c, respectively. Only 1c is ML-active among all four molecules. Single-crystal structural analysis revealed that isomerization of a substituent group affected their molecular packing and intermolecular interactions. Stronger intermolecular interaction and intact three-dimensional hydrogen-bonded networks were formed only in crystal 1c, which were essential for preventing slippage of molecular layers and generating ML; the other molecules were either lacking π-π interactions or C-H···π interactions. Theoretical calculation suggested that the energy barrier between the Franck-Condon (FC) structure and minimum energy crossing point (MECP) structure of 2/3 was much lower than that of 1/4. Nonradiative decay channels of molecules 2 and 3 were thus more easily activated, which led to their lower quantum yield.

Tapered Optical Fibers Coated with Rare-Earth Complexes for Quantum Applications.

Crystals and fibers doped with rare-earth (RE) ions provide the basis for most of today’s solid-state optical systems, from lasers and telecom devices to emerging potential quantum applications such as quantum memories and optical to microwave conversion. The two platforms, doped crystals and doped fibers, seem mutually exclusive, each having its own strengths and limitations, the former providing high homogeneity and coherence and the latter offering the advantages of robust optical waveguides. Here we present a hybrid platform that does not rely on doping but rather on coating the waveguide—a tapered silica optical fiber—with a monolayer of complexes, each containing a single RE ion. The complexes offer an identical, tailored environment to each ion, thus minimizing inhomogeneity and allowing tuning of their properties to the desired application. Specifically, we use highly luminescent Yb3+[Zn(II)MC (QXA)] complexes, which isolate the RE ion from the environment and suppress nonradiative decay channels. We demonstrate that the beneficial optical transitions of the Yb3+ are retained after deposition on the tapered fiber and observe an excited-state lifetime of over 0.9 ms, on par with state-of-the-art Yb-doped inorganic crystals.