Photoinduced Absorption Research Articles

Analyzing the Temperature Dependence of Titania Photocatalysis: Kinetic Competition between Water Oxidation Catalysis and Back Electron-Hole Recombination.

This study examines the kinetic origins of the temperature dependence of photoelectrochemical water oxidation on nanostructured titania photoanodes. We observe that the photocurrent is enhanced at 50 °C relative to 20 °C, with this enhancement being most pronounced (by up to 70%) at low anodic potentials (<+0.6 V vs RHE). Over this low potential range, the photocurrent magnitude is largely determined by kinetic competition between water oxidation catalysis (WOC) and recombination between surface holes and bulk electrons (back electron-hole recombination, BER). We quantify the BER process by transient photocurrent analyses under pulsed irradiation. Remarkably, we find that the kinetics of BER (∼90 ms half-time) are independent of temperature. In contrast, the kinetics of WOC, determined from the analysis of the photoinduced absorption of accumulated surface holes, are found to accelerate up to 2-fold at 50 °C relative to 20 °C. We conclude that the enhanced photocurrent densities observed in the low-applied potential region result primarily from the accelerated WOC, reducing losses due to the competing BER pathway. At higher applied potentials (>+0.6 V vs RHE), a smaller (∼10%) enhancement in photocurrent density is observed at 50 °C relative to 20 °C. Photoinduced absorption studies, correlated with studies using triethanolamine as a hole scavenger, indicate that this more modest enhancement at anodic potentials primarily results from an enhanced charge separation efficiency. We conclude by discussing the implications of these results for the practical application of photoanodic WOC under solar irradiation, influenced by these temperature-independent and -dependent underlying kinetic processes.

Confining CsPbI3 perovskite in metal organic framework (MOF-545) as stable composite photocatalyst for efficient oxygen-tolerant NIR light-driven atom transfer radical polymerization

Zirconium-porphyrin metal-organic framework (MOF-545) encapsulated all inorganic iodide perovskite (CsPbI3) composite (CsPbI3@MOF-545) is used as highly efficient photocatalyst to catalyze NIR light induced atom transfer radical polymerization (ATRP). The combination of CsPbI3 and MOF-545 leads to a synergistic effect with enhanced photoinduced carrier separation and light absorption performance in the composite photocatalyst. The constructed CsPbI3@MOF-545(10 %) can efficiently catalyze the conversion more than 90 % of various monomers under 810 nm NIR light irradiation. Strong oxygen-resistance has been confirmed in the CsPbI3@MOF-545(10 %) catalyzed photo-ATRP system. In a large-volume photo-ATRP system (100 mL), the polymerization of methyl methacrylate (MMA) achieved a conversion over 90 % in 10 h using NIR light in air. The success of chain extension and block polymerization indicates good end-chain fidelity for the synthesized polymers. The composite photocatalyst still displays high photocatalytic activity for the synthesis of polymers with controllable dispersity after seven photopolymerization cycles, demonstrating its promising potential for practical applications.

Facet-Engineered BiVO4 Photocatalysts for Water Oxidation: Lifetime Gain Versus Energetic Loss.

A limiting factor to the efficiency of water Oxygen Evolution Reaction (OER) in metal oxide nanoparticle photocatalysts is the rapid recombination of holes and electrons. Facet-engineering can effectively improve charge separation and, consequently, OER efficiency. However, the kinetics behind this improvement remain poorly understood. This study utilizes photoinduced absorption spectroscopy to investigate the charge yield and kinetics in facet-engineered BiVO4 (F-BiVO4) compared to a non-faceted sample (NF-BiVO4) under operando conditions. A significant influence of preillumination on hole accumulation is observed, linked to the saturation and, thus, passivation of deep and inactive hole traps on the BiVO4 surface. In DI-water, F-BiVO4 shows a 10-fold increase in charge accumulation (∼5 mΔOD) compared to NF-BiVO4 (∼0.5 mΔOD), indicating improved charge separation and stabilization. With the addition of Fe(NO3)3, an efficient electron acceptor, F-BiVO4 demonstrates a 30-fold increase in the accumulation of long-lived holes (∼45 mΔOD), compared to NF-BiVO4 (∼1.5 mΔOD) and an increased half-time, from 2 to 10 s. Based on a simple kinetic model, this increase in hole accumulation suggests that facet-engineering causes at least a 50-100 meV increase in band bending in BiVO4 particles, thereby stabilizing surface holes. This energetic stabilization/loss results in a retardation of OER relative to NF-BiVO4. This slower catalysis is, however, offset by the observed increase in density and lifetime of photoaccumulated holes. Overall, this work quantifies how surface faceting can impact the kinetics of long-lived charge accumulation on metal oxide photocatalysts, highlighting the trade-off between lifetime gain and energetic loss critical to optimizing photocatalytic efficiency.

High Ambipolar Mobility and Long-Range Carrier Transport in Violet Phosphorus Nanosheet.

Carrier transport capacity with high mobility and long-range diffusion length holds particular significance for the advancement of modern optoelectronic devices. Herein, we have unveiled the carrier dynamics and transport properties of a pristine violet phosphorus (VP) nanosheet by a transient absorption microscopy. Under the excitation (2.41 eV) above the exciton band, two photoinduced absorption peaks with the energy difference of approximately 520 meV emerge within a broadband transient absorption background which originates from the prompt generation of free carriers and the concomitant formation of excitons (lifetime of 467.21 ps). This observation is consistent with the established band-edge model of VP. Intriguingly, we have determined the ambipolar diffusion coefficient and mobility of VP to be approximately 47.32 cm2·s-1 and 1798 cm2·V-1·s-1, respectively, which further indicate a long-range carrier transport of approximately 2.10 μm. This work unveils the significant carrier transport capacity of VP, highlighting its potential for future optoelectronic and excitonic applications.

Unraveling the Deep‐Level Defects Induced Optical Losses in LilnSe2 Crystal toward Enhancement of Mid‐Infrared Laser Radiation

AbstractMid‐infrared (MIR) lasers generated by nonlinear optical (NLO) crystals have aroused extensive attention in various military and civilian applications. Among the MIR NLO crystal family, LiInSe2 (LISe) is a promising candidate in the generation of MIR lasers due to its wide transmission range, large bandgap, and high laser‐induced damage threshold. However, the intrinsic defects in LISe induce optical losses, which will induce laser damage and hinder the performance of MIR laser generation. In this work, the mechanism of optical absorption induced by defects is revealed in LISe through transient absorption (TA) spectroscopy. It is verified that the deep‐level defects in LISe give rise to the extra optical absorption, which is owing to the excited state absorption (ESA) and photo‐induced absorption (PIA). Accordingly, for improving the optical properties of LISe crystals, Li2Se vapor‐mediated annealing to reduce defects concentration is rationally designed. The results confirmed that the optical properties of annealed LISe are improved due to the decrease of defects concentration. Ultimately, the performance of MIR laser generation is successfully enhanced by using the annealed LISe crystal. This work provides deep insights into the defect‐induced absorption losses in LISe crystals and promotes the application of LISe crystals in MIR laser generation.

Photoexcited Polaron Relaxation as a Structurally Sensitive Reporter of Charge Trapping in a Conducting Polymer

AbstractConjugated polymers (CPs) play a central role in electronic applications due to their easily tuned electronic and ionic conductivities via chemical or electrochemical doping. Although doping improves charge conduction by introducing high densities of carriers into the CP, the accompanying structural changes and their impact on carrier mobility remain elusive. Methods capable of probing carrier distributions and their dependence on polymer morphology are needed to better understand how to improve conductivity. Here, a transient absorption (TA) spectroscopy approach is demonstrated, capable of directly probing mobile and trapped carriers in doped CPs and that is also sensitive to polymer nanostructure by using a model polythiophene system with tuned crystallinity. Exciting polarons in the polymer films produces distinct photoinduced absorption signals in the near‐infrared spectrum that decay during the picosecond timescale in the form of biphasic, stretched exponential kinetics, which reflect a distribution of mobile (free) and trapped polarons. The kinetic analysis provides evidence for mobile polarons irrespective of polymer film crystallinity, whereas polarons located in impure amorphous phases with reduced chain ordering exist within a deeper distribution of trap states. Altogether, these observations suggest a stronger correlation of carrier trapping with local chain ordering (planarity or aggregation) rather than polymer crystallinity.

Commonly Existing Hole-Capturer Organics Adsorption-Induced Recombination over Metal/Semiconductor Perimeters: A Possible Important Factor Affecting Photocatalytic Efficiencies.

Photocatalysis is a physiochemical effect arising from the relaxation of photoinduced electrons from the conduction band to the valence band. Controlling the electron relaxation to occur through photocatalytic pathways and prohibiting other relaxations is the main scientific thought for photocatalytic studies. It is needed to know the parallel relaxation pathways that can compete with photocatalytic reactions. By means of in situ photoconductances (PCs) and photoinduced absorptions (PAs), the current research studied the photoinduced electron relaxations of the Au/TiO2 in different atmospheres and at different temperatures. The PC and PA relaxations became different and fast when methanol, ethanol, isopropanol, and acetone were introduced; they also tend to decrease as temperature increases, while that of the undecorated TiO2 in all atmospheres and the Au/TiO2 in pure N2 increased. The results indicated that the organic adsorptions over the Au/TO2 perimeters change the relaxation pathway, and a hole-capturing organics adsorption-induced recombination over the Au/TiO2 perimeter was proposed to explain the relaxations. We found that this relaxation also exists for Ag/TiO2, Pt/TiO2, and Au/ZnO, so it is a commonly existing physical course for the metal/semiconductor (M/S) materials. The effect of the organics and M/S structures on the relaxation was discussed, and the relationship with photocatalytic reactions was also analyzed. Our finding means that blocking this relaxation pathway is an effective way to increase photocatalytic activities, which might open a door for highly active photocatalyst developments.

Ultrafast Exciton Dynamics of CH3NH3PbBr3 Perovskite Nanoclusters.

Exciton dynamics of perovskite nanoclusters has been investigated for the first time using femtosecond transient absorption (TA) and time-resolved photoluminescence (TRPL) spectroscopy. The TA results show two photoinduced absorption signals at 420 and 461 nm and a photoinduced bleach (PB) signal at 448 nm. The analysis of the PB recovery kinetic decay and kinetic model uncovered multiple processes contributing to electron-hole recombination. The fast component (∼8 ps) is attributed to vibrational relaxation within the initial excited state, and the medium component (∼60 ps) is attributed to shallow carrier trapping. The slow component is attributed to deep carrier trapping from the initial conduction band edge (∼666 ps) and the shallow trap state (∼40 ps). The TRPL reveals longer time dynamics, with modeled lifetimes of 6.6 and 93 ns attributed to recombination through the deep trap state and direct band edge recombination, respectively. The significant role of exciton trapping processes in the dynamics indicates that these highly confined nanoclusters have defect-rich surfaces.

Thickness-dependent electronic relaxation dynamics in solution-phase redox-exfoliated MoS2 heterostructures.

Electronic relaxation dynamics of solution-phase redox-exfoliated molybdenum disulfide (MoS2) monolayer and multilayer ensembles are described. MoS2 was exfoliated using polyoxometalate (POM) reductants. This process yields a colloidal heterostructure consisting of MoS2 2D sheet multilayers with surface-bound POM complexes. Using two-dimensional electronic spectroscopy, transient bleaching and photoinduced absorption signals were detected at excitation/detection energies of 1.82/1.87 and 1.82/1.80eV, respectively. Approximate 100-fs bandgap renormalization (BGR) and subsequent defect- and phonon-mediated relaxation on the picosecond timescale were resolved for several MoS2 thicknesses spanning from 1 to 2 L to ∼20 L. BGR rates were independent of sample thickness and slightly slower than observations for chemical vapor deposition-grown MoS2 monolayers. However, defect-mediated relaxation accelerated ∼10-fold with increased sample thicknesses. The relaxation rates increased from 0.33 ± 0.05 to 1.2 ± 0.1 and 3.1 ± 0.4ps-1 for 1-2 L, 3-4 L, and 20 L fractions. The thicknesses-dependent relaxation rates for POM-MoS2 heterostructures were modeled using a saturating exponential function that showed saturation at thirteen MoS2 layers. The results suggest that the increased POM surface coverage leads to larger defect density in the POM-MoS2 heterostructure. These are the first descriptions of the influence of sample thickness on electronic relaxation rates in solution-phase redox-exfoliated POM-MoS2 heterostructures. Outcomes of this work are expected to impact the development of solution-phase exfoliation of 2D metal-chalcogenide heterostructures.

Transient Absorption Spectroscopy of Films: Impact of Refractive Index.

Transient absorption spectroscopy is a powerful technique to study the photoinduced phenomena in a wide range of states from solutions to solid film samples. It was designed and developed based on photoinduced absorption changes or that photoexcitation triggers a chain of reactions with intermediate states or reaction steps with presumably different absorption spectra. However, according to general electromagnetic theory, any change in the absorption properties of a medium is accompanied by a change in the refractive properties. Although this photoinduced change in refractive index has a negligible effect on solution measurements, it may significantly affect the measured response of thin films. In this Perspective paper, we examine why and how the measured responses of films differ from their expected "pure" absorption responses. The effect of photoinduced refractive index change can be concluded and studied by comparing the transmitted and reflected probe light responses. Another discussed aspect is the effect of light interference on thin films. Finally, new opportunities of monitoring the photocarrier migration in films and studying nontransparent samples using the reflected probe light response are discussed. Most of the examples provided in this article focus on studies involving perovskite, TiO2, and graphene-based films, but the general discussion and conclusions can be applicable to a wide range of semiconductor and thin metallic films.

Photoluminescence Enhancement in Silica-Confined Ligand-Free Perovskite Nanocrystals by Suppression of Silanol-Induced Traps and Phase Impurities.

The detriments of intrinsic silanol groups in mesoporous silica to the photoluminescence (PL) of lead halide perovskite nanocrystals (LHP NCs) confined in the template have never been determined and clearly elucidated. Here, we disclose that silanol-induced Cs+ and Br- deficiencies prompt the generation of traps and CsPb2Br5 impurities. The temperature-dependent PL spectra verify the higher energetic barrier of trap states in CsPbBr3 NCs confined in silanol-rich mesoporous silica. Femtosecond transient absorption spectra reveal the trapped state mediates a broadband photoinduced absorption and long-lived decay pathway of CsPbBr3 NCs in silanol-rich templates. A remarkable improvement (up to 160-fold) in PL quantum yields is realized by simple silanol elimination. This work demonstrates the detrimental effects of silanol sites on the PL properties of LHP NCs impregnated in mesoporous silica and provides a new perspective for the ligand-free synthesis of high-quality LHP NCs in mesoporous templates by facile impregnation for practical applications.

Ultrafast Dynamics, Optical Nonlinearities, and Chemical Sensing Application of Free-Standing Porous Silicon-Based Optical Microcavities.

The present work demonstrates the ultrafast carrier dynamics and third-order nonlinear optical properties of electrochemically fabricated free-standing porous silicon (FS-PSi)-based optical microcavities via femtosecond transient absorption spectroscopy (TAS) and single-beam Z-scan techniques, respectively. The TAS (pump: 400 nm, probe: 430-780 nm, ∼70 fs, 1 kHz) decay dynamics are dominated by the photoinduced absorption (PIA, lifetime range: 4.7-156 ps) as well as photoinduced bleaching (PIB, 4.3-324 ps) for the cavity mode (λc) and the band edges. A fascinating switching behavior from the PIB (-ve) to the PIA (+ve) has been observed in the cavity mode, which shows the potential in ultrafast switching applications. The third-order optical nonlinearities revealed an enhanced two-photon absorption coefficient (β) in the order of 10-10 mW-1 along with the nonlinear refractive index (n2) in the range of 10-17 m2 W-1. Furthermore, a real-time sensing application of such FS-PSi microcavities has been demonstrated for detecting organic solvents by simultaneously monitoring the kinetics in reflection and transmission mode.

Photoluminescence Enhancement in Silica‐Confined Ligand‐Free Perovskite Nanocrystals by Suppression of Silanol‐Induced Traps and Phase Impurities

AbstractThe detriments of intrinsic silanol groups in mesoporous silica to the photoluminescence (PL) of lead halide perovskite nanocrystals (LHP NCs) confined in the template have never been determined and clearly elucidated. Here, we disclose that silanol‐induced Cs+ and Br− deficiencies prompt the generation of traps and CsPb2Br5 impurities. The temperature‐dependent PL spectra verify the higher energetic barrier of trap states in CsPbBr3 NCs confined in silanol‐rich mesoporous silica. Femtosecond transient absorption spectra reveal the trapped state mediates a broadband photoinduced absorption and long‐lived decay pathway of CsPbBr3 NCs in silanol‐rich templates. A remarkable improvement (up to 160‐fold) in PL quantum yields is realized by simple silanol elimination. This work demonstrates the detrimental effects of silanol sites on the PL properties of LHP NCs impregnated in mesoporous silica and provides a new perspective for the ligand‐free synthesis of high‐quality LHP NCs in mesoporous templates by facile impregnation for practical applications.

An All‐Colloidal and Eco‐Friendly Quantum‐Dot Laser

AbstractColloidal zinc‐chalcogenide quantum dots (QDs) are emerging as the promising heavy‐metal‐free light–emitters, however, the development of light amplification and lasing therein remains challenging. Here, corroborated by comprehensive in situ and transient spectroscopy, it is unraveled that the ultrafast photooxidization‐induced trapping process (≈2 ps) and the sub‐bandgap photoinduced absorption under intense excitation are the main hindrances to light amplification in ZnSeTe QDs. Upon tackling the hurdle by heterostructure engineering, this study demonstrates that the ZnSeTe QDs exhibit intrinsically superior gain performance, including the high gain cross‐section (5.6 × 10−16 cm2), long gain lifetime (615 ps), low pump threshold (≈25.9 µJ cm−2) and high fatigue resistance. On this basis, a microfluidic channel is designed to mass‐produce the micellar cavities whose surfaces are treated to combine with the ZnSeTe QDs. The active QD‐micelle hybrids show state‐of‐the‐art lasing performance and allow the fiber‐based micro‐manipulation toward the single‐mode lasers. These findings not only provide essential knowledge on the gain physics in ZnSeTe QDs, but also open a new avenue to develop high‐performance eco‐friendly lasers.

Exploring the Early Time Behavior of the Excited States of an Archetype Thermally Activated Delayed Fluorescence Molecule.

Optical pump-probe techniques allow for an in-depth study of dark excited states. Here, we utilize them to map and gain insights into the excited states involved in the thermally activated delayed fluorescence (TADF) mechanism of a benchmark TADF emitter DMAC-TRZ. The results identify different electronic excited states involved in the key TADF transitions and their nature by combining pump-probe and photoluminescence measurements. The photoinduced absorption signals are highly dependent on polarity, affecting the transition oscillator strength but not their relative energy positions. In methylcyclohexane, a strong and vibronically structured local triplet excited state absorption (3LE → 3LEn) is observed, which is quenched in higher polarity solvents as 3CT becomes the lowest triplet state. Furthermore, ultrafast transient absorption (fsTA) confirms the presence of two stable conformers of DMAC-TRZ: (1) quasi-axial (QA) interconverting within 20 ps into (2) quasi-equatorial (QE) in the excited state. Moreover, fsTA highlights how sensitive excited state couplings are to the environment and the molecular conformation.

CO2 Pressure‐Induced Self‐Trapped Excitons in SrTiO3

With strong electron–phonon coupling, self‐trapped excitons (STEs) are typically formed in perovskite materials, and radiative recombination of STEs can produce broadband emission with large Stokes shifts. STEs are essential to further improve the optoelectronic properties of materials. Surprisingly, 2D system is the edge case, with low even no self‐trapping barriers, leading to effortless formation of STEs. In this work, 2D strontium titanate (SrTiO3) with defects is prepared using supercritical carbon dioxide (SC CO2) and its carrier transport and transition are studied. The appearance of wide photoinduced positive absorption signals in the femtosecond transient absorption spectra is direct evidence for the formation of STEs. The presence of STEs is further supported by the increased Stokes shift and full width at half maximum in the steady‐state photoluminescence spectra.

Photoinduced absorption and linear/nonlinear emission of assembled carbon dot–silica nanocomposites for cellular imaging

Silanized carbon dot (CD–SiO2) composites show transformation from saturable absorption to anti-saturation absorption, and the PIA phenomenon was first investigated in the CD-based field by ns-TA spectroscopy.

(Invited) Operando Optical Spectroscopy Analyses of Photoelectrochemical Water Oxidation Kinetics

Water oxidation is a key kinetic bottleneck in many photoelectrochemical systems for solar to fuels and chemicals. We have recently been developing an operando optical spectroscopic analysis to assay these reaction kinetics in metal oxide photoanodes. This technique, which we refer to as photoinduced absorption spectroscopy, is based around measuring the optical absorption of oxidising species (‘surface holes’) generated in photoanodes under anodic bias and pulsed (typically 5 s) light irradiation. These analyses have allowed us to observe a non-linear dependence of water oxidation kinetics on surface hole density, most typically a 3rd order rate law dependence under circa 1 sun irradiation conditions. In my talk I will talk about three different applications of this PIAS approach to investigate the function of BiVO4, Fe2O3 and TiO2 photoanodes. Firstly I will discuss how this non-linear dependence can be exploited to determine the photoelectrochemically active surface area of photoanodes as function of metal oxide nanostructuring. I will then go on to demonstrate that, when normalised for matched surface hole densities, water oxidation kinetics measured in under light irradiation or in the dark at strong anodic bias are identical, and discuss how this conclusion can be exploited to quantify the photovoltage under irradiation. Finally I will discuss deviation from rate law behaviour observed under > 1 sun irradiation conditions, and its mechanistic origin.

Molecular Control of Triplet-Pair Spin Polarization and Its Optoelectronic Magnetic Resonance Probes.

ConspectusPreparing and manipulating pure magnetic states in molecular systems are the key initial requirements for harnessing the power of synthetic chemistry to drive practical quantum sensing and computing technologies. One route for achieving the requisite higher spin states in organic systems exploits the phenomenon of singlet fission, which produces pairs of triplet excited states from initially photoexcited singlets in molecular assemblies with multiple chromophores. The resulting spin states are characterized by total spin (quintet, triplet, or singlet) and its projection onto a specified molecular or magnetic field axis. These excited states are typically highly polarized but exhibit an impure spin population pattern. Herein, we report the prediction and experimental verification of molecular design rules that drive the population of a single pure magnetic state and describe the progress toward its experimental realization.A vital feature of this work is the close partnership among theory, chemical synthesis, and spectroscopy. We begin by presenting our theoretical framework for understanding spin manifold interconversion in singlet fission systems. This theory makes specific testable predictions about the intermolecular structure and orientation relative to an external magnetic field that should lead to pure magnetic state preparation and provides a powerful tool for interpreting magnetic spectra. We then test these predictions through detailed magnetic spectroscopy experiments on a series of new molecular architectures that meet one or more of the identified structural criteria. Many of these architectures rely on the synthesis of molecules with features unique to this effort: rigid bridges between chromophores in dimers, heteroacenes with tailored singlet/triplet-pair energy level matching, or side-group engineering to produce specific crystal structures. The spin evolution of these systems is revealed through our application and development of several magnetic resonance methods, each of which has different sensitivities and relevance in environments relevant to quantum applications.Our theoretical predictions prove to be remarkably consistent with our experimental results, though experimentally meeting all the structural prescriptions demanded by theory for true pure-state preparation remains a challenge. Our magnetic spectra agree with our model of triplet-pair behavior, including funneling of the population to the ms = 0 magnetic sublevel of the quintet under specified conditions in dimers and crystals, showing that this phenomenon is subject to control through molecular design. Moreover, our demonstration of novel and/or highly sensitive detection mechanisms of spin states in singlet fission systems, including photoluminescence (PL), photoinduced absorption (PA), and magnetoconductance (MC), points the way toward both a deeper understanding of how these systems evolve and technologically feasible routes toward experiments at the single-molecule quantum limit that are desirable for computational applications.

High‐Gain Waveguide Amplifiers in Ge25Sb10S65Photonics Heterogeneous Integration with Erbium‐Doped Al2O3Thin Films

AbstractHigh‐efficiency optical waveguide amplifiers are becoming desperately desirable in integrated photonics to provide sufficient power compensations. Various material platforms have been employed to realize on‐chip waveguide amplifiers to date. Chalcogenide glasses (ChGs), as one of the well‐developed and promising optical platforms, have been extensively studied due to the excellent properties of low loss and high third‐order nonlinearity. However, the performances of their waveguide amplifiers are far from expectations on account of the intrinsic natures of low rare‐earth ion solubility, low luminous efficiency in chalcogenide hosts as well as the high photoinduced absorption loss in certain compounds. Here, a heterogeneous optical amplifier is proposed and demonstrated in an alternative Ge25Sb10S65(GeSbS) waveguide via integration with an erbium‐doped aluminum oxide (Al2O3) layer for the first time. A total 4.6 cm long spiral waveguide exhibits an internal net gain as high as 6.27 ± 0.618 dB at 1533 nm and a broad gain bandwidth over 40 nm ‐ ranging from 1520 nm to 1560 nm upon 1480 nm pumping. It is believed that this heterogeneous configuration will greatly enrich the functionality and versatility of the ChGs integrated photonics.