Coordination-driven self-assembly provides an effective strategy for the precise construction of supramolecular nonlinear optical (NLO) materials, yet its potential in third-order NLO applications remains insufficiently explored. Herein, we report a rhombic Pt(II) metallacycle (MPt) constructed via Pt-N coordination-driven self-assembly, achieving markedly enhanced third-order NLO responses that are confirmed to originate from the formation of the metallacyclic structure. Benefiting from the enhanced spin-orbit coupling (SOC) induced by multinuclear Pt(II) nodes and framework rigidification, MPt promotes intersystem crossing (ISC), suppresses triplet-state nonradiative decay, prolongs the triplet-state lifetime to 8.18 μs and strengthens excited-state absorption (ESA). As a result, MPt displays pronounced reverse saturable absorption (RSA) at 532 nm, outperforming the benchmark NLO material C60. Furthermore, the fabricated MPt@PDMS film exhibits excellent optical power limiting (OPL) performance, with an effective nonlinear absorption coefficient (βeff) of 1045.70 cm GW-1 and a low optical limiting threshold (FOL) of 0.23 J cm-2, placing it among the best-performing polymer-based OPL films reported to date. This work provides valuable insight into the rational design of high-performance supramolecular NLO assemblies and establishes supramolecular topological engineering as an effective strategy for amplifying third-order NLO responses.

Chromophores with short photoluminescence lifetimes are highly desirable for minimizing exciton-exciton annihilation, suppressing triplet accumulation, and enabling ultrafast modulation in applications such as time-resolved imaging, high-speed data transmission, and light fidelity (Li-Fi). However, achieving rapid excited-state dynamics without compromising emission efficiency remains a significant challenge. Here, we report three solution-processable oligophenylene-based chromophores, Monomer, Dimer, and Trimer, functionalized with phenylcarbazole end caps. Through systematic structure-property modulation, these chromophores exhibit remarkably short photoluminescence lifetimes (down to 0.43 ns), high molar absorption coefficients (up to 236,000 M-1 cm-1 at 399 nm), and large radiative decay rates (up to 2.08 × 109 s-1). In the context of organic lasing, they also show large emission cross sections (up to 1.01 × 10-15 cm2), minimal spectral overlap between excited-state absorption and amplified spontaneous emission (ASE), and very low solid-state ASE thresholds (0.67-0.80 μJ cm-2) in the deep blue region. Computational studies attribute these properties to extended π-conjugation and high HOMO-LUMO overlap along the predominantly planar oligophenylene backbone, which enhances π-delocalization and oscillator strengths. Electroluminescent studies through fabrication of organic light-emitting diodes gave external quantum efficiencies up to 3.2%. These findings highlight the effectiveness of molecular engineering in accelerating excited-state decay while maintaining efficient light emission, establishing a promising platform for next-generation lasers, optical communications, ultrafast displays, and broadband photonic technologies.

Unveiling the intramolecular photophysical transitions and intrinsic excited-state dynamics of organometallic complexes is of critical importance yet remains challenging. Herein, two platinum (II)-acetylide triads, namely Pt-1 bearing the triethylphosphine ligands and Pt-2 with the triphenylphosphine ligands, were rationally synthesized and investigated comprehensively. The NMR shielding phenomena of Pt(II) atoms with dense extranuclear electrons are elucidated properly through comparative studies on a reference analogue, BDT-TPA. The rigid planar molecular geometries endow the triads with extended π-conjugation, which promotes efficient ligand-to-metal charge transfer (LMCT) and ligand-to-ligand charge transfer (LLCT). Furthermore, a significant effect of Pt(II)-acetylide d-π coordination, ligand aromaticity, and steric hindrance on the steady state and nonlinear optical properties are also elucidated comparatively. Benefiting from strong spin-orbit coupling and ligand-mediated conjugation, both Pt(II)-acetylide triads exhibit enhanced intersystem crossing rates and prolonged triplet-state lifetimes. Notably, Pt-2 displays a maximum two-photon absorption cross-section of 1830 GM in THF upon femtosecond excitation at 650 nm, which is obviously higher than that of 980 GM at 775 nm observed for BDT-TPA. High-performance optical power limiting assessments based on the two-photon absorption mechanism reveal that both triads possess low onset thresholds around 0.06 J·cm-2 and favorable limiting thresholds around 0.25 J·cm-2. Theoretical calculations further correlate the superior nonlinear optical performance with efficient excited-state absorption as well as prominent LMCT characteristics. This study not only affords mechanistic insights into the intrinsic photophysics of the Pt(II)-acetylide complexes but also sheds light on the potential nonlinear optical applications.

Transient absorption experiments have previously been carried out to study the excited-state dynamics of atomically precise gold nanoparticles such as Au25 and Au38. Different mechanisms have been proposed to explain the excited-state dynamics on various time scales, ranging from femtoseconds to nanoseconds. In this work, we perform ab initio transient absorption simulations to investigate the excited-state dynamics of Au25 and Au38, which enables state-specific resolution. For Au25, pump energies corresponding to peaks in its optical absorption spectrum were applied to excite the nanocluster. By a detailed analysis of orbitals, we separated the contributions to excited-state absorption that arise from electrons and holes. For Au25, the lowest-energy sub-100 fs dynamics arise from transitions among d electrons in gold, whereas higher-energy dynamics originate from transitions between superatomic dynamics. This ab initio state-resolved dynamics process agrees well with the rapid ligand-independent decay in the experiment. For Au38, different energies and directions of the pump laser are applied to induce absorption polarized in different directions. The higher-energy dynamics in Au38 tend to arise from transitions between superatomic orbitals, whereas the lowest-energy excited-state absorption (below 0.5 eV) originates from hole dynamics among d-band orbitals. Because of symmetry and polarizability, the induced dipole moment in anisotropic Au38 remains in the direction of the pump for our simulation time scale, whereas the more isotropic Au25 nanocluster is better able to transfer the energy from the pump to the other two polarization directions.

Thin films doped with rare‐earth ions often suffer from poor crystallinity and low up‐conversion quantum yield (UCQY), limiting their use in photonic and energy‐conversion devices. Nd 3+ ions remain particularly underexplored when doped in thin‐film, with no established route for achieving efficient visible up‐conversion (UC). Here, we develop an aerosol‐assisted chemical vapor deposition (AACVD) process operated at atmospheric pressure to fabricate Nd 3+ ZnO thin films on Si(111). Systematic variation of the deposition temperature (370–500°C), followed by post‐annealing at 1000°C, reveals a direct correlation between Nd incorporation, ZnO crystallinity, and UCQY. Films deposited at 430°C incorporate 2.97 at.% Nd and exhibit optimal c ‐axis orientation and a refractive index of ~2.03. Under 808 nm excitation, these films display strong visible UC emissions at 540, 618, and 680 nm, achieving a total UCQY of 4.25 ± 0.1%. Mechanistic analysis indicates a two‐photon process involving excited‐state absorption (ESA), energy transfer (ET), cooperative energy transfer (CET), and cross‐relaxation (CR), with concentration quenching occurring above ~3 at.% Nd. This study presents a temperature‐dependent AACVD method that optimizes Nd incorporation and ZnO microstructure for efficient visible UC. This provides a cost‐effective and scalable pathway for high‐performance Nd‐activated photonic thin films.

The escalating demand for reliable protection against high-fluence laser pulses across industrial, defense, and biomedical fields has driven intensive research into advanced optical limiting materials. A critical challenge remains the often-high operational threshold of such devices, which limits their sensitivity and practical deployment. Herein, we report the rational design and synthesis of a series of isostructural Ln3+-porphyrinic metal-organic frameworks (MOFs, Ln3+ = Gd, Tb, Er) that exhibit exceptional reverse saturable absorption (RSA). Remarkably, the erbium-based analogue (Er-TCPP) exhibits a giant third-order nonlinear absorption coefficient of 4.86 × 10-4 m/W and an ultralow starting threshold of 1.42 mJ/cm2 at 532 nm using the Z-scan technique. A synergistic mechanism is unveiled through combined femtosecond transient absorption spectroscopy and density functional theory (DFT + U) calculations. The giant third-order nonlinear response of Er-TCPP is likely driven by the combined effects of spin-orbit coupling and f-state-mediated excited-state interactions, together with the extensive electronic delocalization within the 18π-electron conjugated framework of the TCPP ligand, all of which collectively prolong excited-state carrier lifetimes and substantially enhance excited-state absorption. This study not only reports a state-of-the-art MOF with exceptional optical limiting performance but also establishes a general design principle based on targeted metal-ligand electronic synergy for developing advanced nonlinear optical materials.

This paper discusses the numerical optimization of a fiber laser in which the principal source of intracavity loss is the excited-state absorption of active ions. The laser model considers the laser, spontaneous emission, and pump waves propagating along the gain fiber. It also considers wavelength-dependent radial distributions of these waves and radially varying populations of energy levels in the active ions, both of which are crucial for maintaining the law of conservation of energy. The results show that the optimal reflection of the output mirror in the laser cavity depends on both the length of the gain fiber and the pump power. Furthermore, the study demonstrates that there exists an optimal set of laser parameters—such as the output mirror reflectivity, gain fiber length, and pump power—that yields the maximum laser efficiency. Any deviation from these parameters, including changes in pump power, significantly diminishes efficiency.

Transient ground-state bleaching (GSB), stimulated emission (SE), and excited-state absorbance (ESA) are measured for betaine-30 (B30) in the first excited singlet state (S1) on picosecond time scales. In the viscous solvents glycerol, ethylene glycol, and deep eutectic solvents with intermediate viscosities, SEis seen to the red of the ground-state absorption band and ESA at shorter wavelengths. By contrast, SEis not seen in the nonviscous solvents acetone and ethyl acetate, although both GSB and ESA are prominent. Fluorescence is detectable at room temperature in ethylene glycol and glycerol and increases as the temperature is lowered but is not seen in acetone or ethyl acetate. The absence of SEand fluorescence in nonviscous solvents is consistent with previous suggestions that S1 can relax to a conformation in which radiative transitions to the ground state (S0) are forbidden. Viscous solvents evidently suppress this relaxation. Time-dependent DFT calculations for B30 in various solvents show that the relaxed configuration is strongly twisted. Molecular orbitals, excitation energies, and oscillator strengths are calculated for structures on minimum-energy paths for twisting using six different density functionals, including spin-opposite, range-separated double-hybrid functionals optimized for excited states. As the molecule twists, the oscillator strength for S0-S1 transitions decreases while ESA shifts to shorter wavelengths. Excitation from S0 to S1 has substantial π-π* character in the ground-state conformation but becomes almost entirely a charge-transfer transition as S1 relaxes, accounting for the loss of oscillator strength. The need for solvent rearrangement explains the sensitivity of the relaxation dynamics to viscosity and temperature.

Sm3+-doped antimony-tungsten-phosphate glasses (designated SWNSm) with the composition (40 - x) Sb2O3-10WO3-50NaPO3-xSm2O3 (x = 0.15, 0.30, 0.45, 0.60, and 0.75 mol%) were prepared by the conventional melt-quenching-annealing technique. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses confirmed the amorphous nature and excellent thermal stability of the prepared glasses. Both experimental and theoretical elastic parameters, including Young's modulus (E) and Poisson's ratio (ν), were evaluated to verify that the incorporation of Sm3+ ions does not compromise the mechanical stiffness of the host glass. The measured density increased with increasing Sm2O3 content. Vibrational modes were identified using IR and FTIR spectroscopy. The optical bandgap values for all glass compositions were determined to lie in the range of 2.84-2.87 eV, confirming the insulating character of these glasses. Under 402 nm excitation, the down-conversion emission spectra exhibited characteristic transitions: 4G5/2 → 6H5/2 (560 nm), 4G5/2 → 6H7/2 (596 nm), 4G5/2 → 6H9/2 (643 nm), and 4G5/2 → 6H11/2 (707 nm). The observed up-conversion luminescence was interpreted in terms of excited-state absorption (ESA), energy transfer (ET), and cross-relaxation (CR) mechanisms. IR analysis revealed that the low phonon energy of the antimony-based glass host-evidenced by the dominant Sb-O-Sb stretching band at 602 cm-1-results in a reduced multiphonon relaxation rate, thereby facilitating efficient up-conversion processes. With increasing Sm3+ content, the measured fluorescence lifetime decreased from 1.815 to 1.710 ms, which is attributed to the increased concentration of OH- groups and the enhanced probability of ET among Sm3+ ions. The CIE chromaticity coordinates (x, y) fall within the orange-red region, indicating that these glasses are promising candidates for orange-red LED and solid-state laser applications.

Excited-state optical absorption in modified Kratzer–ring-shaped quantum dots

Comprehensive investigation on two-photon absorption enhancement via excited-state charge transfer in terminal modified chalcone derivatives

Exploring the regulatory effect of organic-inorganic hybrid perovskites on the third-order nonlinear optical (NLO) properties of MOFs is of great significance. In this work, we used Co-MOF {[Co1.25(HL)0.5(Pz-NH2)0.25(μ3-O)0.25(μ2-OH)0.25(H2O)]·0.125 Co·0.125 L·10.25 H2O}(where L = 5,5'-(1H-2,3,5-triazole-1,4-diyl)diisophthalic acid) as the host framework and confined the outstanding optical properties guest molecules AaPbXb {X = Br or I; A = 4BrMBA (a = 2; b = 4) or MBA (a = 1; b = 3)} into the cavities, investigating the regulatory effect of perovskite on the third-order NLO properties of Co-MOF. The third-order NLO tests indicated that Co-MOF displays saturated absorption and self-defocusing refraction behaviors, while AaPbXb@Co-MOF demonstrates excellent antisaturated absorption and self-focusing refraction properties. Furthermore, compared with AaPbXb, the third-order nonlinear optical intensity of AaPbXb@Co-MOF has increased by 3 times. Femtosecond transient absorption spectroscopy (fs-TAS), time-resolved pump-probe spectroscopy, and theoretical calculations were employed to investigate the regulatory mechanism of the NLO properties, revealing that Co-MOF exhibits a ground-state bleaching mechanism, (R-4BrMBA)2PbBr4 displays a two-photon absorption mechanism, and (R-4BrMBA)2PbBr4@Co-MOF demonstrates two-photon absorption and two-photon-induced excited-state absorption mechanisms. This study provides a reference for perovskite regulation of MOFs' NLO performance.

Recent theoretical studies highlight how nonclassical photon correlations in entangled photon pairs can selectively address nonlinear optical pathways. However, the resulting signals are typically too weak for practical time-resolved experiments. Here, we propose two-dimensional (2D) time-resolved fluorescence spectroscopy that exploits these correlations and operates with current single-photon detectors. The method provides two advantages over conventional 2D electronic spectroscopy: (i) It yields 2D spectra without phase-stable multipulse control, relying instead on heralded twin-photon correlations, and (ii) it simplifies spectra by isolating the contribution that is spectroscopically equivalent to stimulated emission, thereby suppressing ground-state bleaching and excited-state absorption. Numerical calculations for a natural pigment-protein complex-inspired trimer show that this pathway selectivity enables the extraction of rich information on energy transfer dynamics. These results indicate a feasible route to real-time observation of molecular dynamics using entangled photon pairs.

The accurate prediction of absorption and emission spectra of molecular compounds using quantum mechanical (QM) methods is essential for understanding and designing laser materials, especially when experimental data are limited or inaccessible or when the syntheses are time- and resource-consuming. In this work, a numerical framework is developed to simulate the laser properties of molecular compounds from first principles. The methodology integrates QM calculations in combination with thermal sampling and a Gaussian Mixture Model-based Nuclear Ensemble Approach (GMM-NEA) for spectra reconstruction, and a spectrally resolved spatiotemporal laser simulation model. The GMM-NEA method is extended to include spontaneous and stimulated emission processes, enabling the generation of spectroscopic input for laser modeling. The framework is validated using two boron hydrides, anti-B18H22 and Et4-anti-B18H18, which exhibit contrasting laser behaviors, while possessing very similar absorption and emission properties. High-level multireference multiconfigurational QM calculations (CASSCF/MS-CASPT2) are employed, and the results show excellent agreement with experimental data. The present framework identifies excited-state absorption as the primary factor responsible for the absence of lasing in Et4-anti-B18H18. This approach represents not only a potentially predictive in-silico screening of candidate laser compounds but also offers deeper physical insight into the behavior of novel laser materials.

Quasi-two-dimensional (quasi-2D) Dion–Jacobson (DJ) perovskites modified with large organic cations exhibit superior optoelectronic properties and stability compared to their three-dimensional (3D) counterparts, making them promising for light-emitting diodes and lasing applications. While diammonium cations with linear chain structures are preferred due to their hydrogen-bonding capability and enhanced structural stability, the effect of cation chain length remains insufficiently understood. Here, we systematically investigate three diammonium spacers with varying chain lengths. Ultrafast spectroscopy reveals that longer-chain cations promote pronounced phase separation, which facilitates the formation of a high-quality n=2 phase, uniform phase distribution, efficient energy transfer, and suppressed non-radiative recombination. These effects collectively reduce the amplified spontaneous emission threshold, from 41.94 μJ/cm2 (EDA, short-chain) and 29.86 μJ/cm2 (BDA, medium-chain) to an ultralow 7.67 μJ/cm2 (PentDA, long-chain). Using this optimized gain medium, we demonstrate a single-mode vertical-cavity laser with a threshold of 6.75 μJ/cm2, a narrow linewidth of 0.49 nm, and a high-quality factor of 1093.8. Conversely, short-chain cations lead to weak phase separation and an insufficient n=2 phase content, resulting in film transient absorption characteristics dominated by excited-state absorption. This study clarifies the critical role of cation chain length in tuning the phase behavior and optical gain of quasi-2D DJ perovskites, providing guidance for their use in low-threshold laser devices.

Nonlinear spectroscopic techniques using entangled photon pairs can provide an opportunity to exploit non-classical correlations encoded in two-photon wave functions to manipulate two-exciton wave functions. We propose an entangled photon pair-enhanced multidimensional spectroscopic technique that is sensitive to exciton-exciton interactions and correlations at the femtosecond timescale. Simulations for a dissipative system, namely, the photosynthetic aggregate, reveal the superior ability of entangled photon pairs, compared to both transform-limited and frequency-chirped laser pulses, to manipulate excited-state absorption pathways. The corresponding spectral features in the two-dimensional spectrogram are interpreted in terms of one- and two-exciton resonances. The signal scales linearly with the incoming intensity of the photon sources. We show that classifying these resonances using an entangled photon source in the perturbative limit allows for probing exciton correlations at the natural energy scale. These insights can be used to explore multi-exciton dynamics in molecular systems using multiphoton entanglement.

We propose a TD-DFT protocol for computing unrelaxed excited-state absorption (ESA) oscillator strengths in solution. Our model is formulated within the popular PCM framework and includes both linear-response and state-specific solvent effects through the cLR2 scheme. This protocol can be applied in two regimes: fast and slow. The former corresponds to situations where the time scale of the entire photophysical process is too short to allow relaxation of the nuclear degrees of freedom of the solvent, whereas the latter allows such relaxation. For selected illustrative examples of S1-Sn ESA transitions in organic dyes, we compare solvated and gas phase transition energies, oscillator strengths, and transition dipole moments. This analysis reveals that solvent-induced shifts in oscillator strengths are predominantly driven by the variations of the transition dipole moment. The magnitude of the solvent effect is strongly system- and state-dependent. For transitions for which S0-geometry states could be unambiguously assigned to their S1-geometry counterparts, we found that the two solvation regimes can lead to significantly different effects on the ESA transition properties. This observation is further confirmed by comparing the two solvation regimes, as well as gas phase results, with experimental ESA spectra extracted from transient spectroscopy measurements. Our scheme exhibits clear improvement over the in vacuo outcomes and correctly reproduces the main regions with intense ESA, although an unambiguous choice between the two regimes remains challenging.

Organic semiconductors have been widely used to fabricate optoelectronic devices due to their low-cost processing, high mechanical flexibility, high tunable emission wavelength, etc. However, the development of a deep blue organic laser remains constrained, and continuous-wave (CW) operation faces significant challenges due to issues such as singlet-triplet annihilation (STA) and triplet accumulation. In this study, we use two synthesized blue organic molecules, 2-(4-(7-(dibenzo[b,d]furan-3-yl)-9,9-dipropyl-9H-fluoren-2-yl)phenyl)-1-phenyl-1H-phenanthro[9,10-d]imidazole (PWO1) and 2-(4-(7-(dibenzo[b,d]furan-4-yl)-9,9-dipropyl-9H-fluoren-2-yl)phenyl)-1-phenyl-1H-phenanthro[9,10-d]imidazole (PWO2), with a hybridized local and charge-transfer (HLCT) mechanism to study their lasing characteristics. We found that the incorporation of fluorene bridges into molecules significantly enhances the oscillator strength, thus greatly reducing the amplified spontaneous emission (ASE) threshold, which reaches values as low as 1.15 and 0.60 μJ cm-2 for PWO1 and PWO2, respectively, and a long operational lifetime of 105 pump pulses under ambient conditions is observed for PWO2. At a high repetition frequency of 200 kHz, which approximates quasi-continuous-wave (qCW) operation, PWO2 exhibits an invariable ASE threshold, indicating its good photostability. The superior lasing performance is attributed to the negligible overlap between the triplet excited-state absorption and ASE spectra. Furthermore, the external quantum efficiency (EQE) values of the fabricated deep blue organic light-emitting diodes based on PWO1 and PWO2 reach values of 8.22% and 7.26%, respectively, with extremely low efficiency roll-off, which is particularly favorable for the high-current injection required for electrically pumped organic lasers.

In this work, we present a theoretical and computational approach that combines real-time propagation of the electronic wave function, the GW/BSE formalism for the electronic structure of ground and excited states, the theory of open quantum systems, and the phase-cycling method to compute two-dimensional electronic spectra (2DES) of molecular systems under realistic excitation conditions. The advantage of this strategy is that it combines the accuracy of first-principle calculations such as GW/BSE with an explicit description of the employed laser pulses. This allows for better adherence to experimental setups. We apply the proposed methodology to benzene, chlorophyll b, and a benzene-phenol dimer, also including a pure electronic dephasing in the time propagation. The calculated 2DES maps reveal clear signatures of stimulated emission and excited-state absorption, as well as coherence dynamics as a function of the population time, both in the absence and presence of pure dephasing. Comparison with experimental and theoretical published data has been carried out, when available.

Rare earth upconversion nanoparticles (UCNPs) have made remarkable progress in overcoming the limitations of traditional optical probes in biomedical applications, such as shallow tissue penetration and strong background interference, owing to the anti-Stokes luminescence properties of near-infrared excitation followed by visible/ultraviolet emission. In this review, we systematically summarized the core luminescence mechanisms, including excited-state absorption, energy transfer upconversion, photon avalanche, and other multipath energy transfer processes, and discussed the optimization progress of the co-precipitation, sol-gel method, hydrothermal, and thermal decomposition methods. This review focused on the latest achievements in improving luminous efficiency through strategies such as core-shell structure design, ion doping regulation, and surface functionalization. In biomedicine, UCNPs have been used for the high-resolution imaging of deep tissues, high-sensitivity biosensing, and precise photodynamic therapy. Moreover, this article systematically reviewed the latest research progress on the biomedical applications of UCNPs. Finally, we proposed a development direction in material design innovation and clinical translation to provide a reference for promoting the development of UCNPs from laboratory research to practical applications.