Tunable Optical Properties Research Articles

Tunable extraordinary optical transmission spectrum properties of long-wavelength infrared metamaterials.

Metamaterial filters represent an essential method for researching the miniaturization of infrared spectral detectors. To realize an 8-2µm long-wave infrared tunable transmission spectral structure, an extraordinary optical transmission metamaterial model was designed based on the grating diffraction effect and surface plasmon polariton resonance theory. The model consisted of an Al grating array in the upper layer and a Ge substrate in the lower layer. We numerically simulated the effects of different structural parameters on the transmission spectra, such as grating height (h), grating width (w), grating distance (d), grating constant (p), and grating length (S 1), by utilizing the finite-difference time-domain method. Finally, we obtained the maximum transmittance of 81.52% in the 8-12µm band range, with the corresponding structural parameters set to h=50n m, w=300n m, d=300n m, and S 1=48µm, respectively. After Lorentz fitting, a full width at half maximum of 0.94±0.01µm was achieved. In addition, the Ge substrate influence was taken into account for analyzing the model's extraordinary optical transmission performance. In particular, we first realized the continuous tuning performance at the transmission center wavelength (8-12µm) of long-wave infrared within the substrate tuning thickness (D) range of 1.9-2.9µm. The structure designed in this paper features tunability, broad spectral bandwidth, and miniaturization, which will provide a reference for the development of miniaturized long-wave infrared spectral filter devices.

Modulation of Excimer Formation and Photoexcitation Behaviour through DNA‐Surfactant‐Dye Supramolecular Assembly

AbstractDNA‐based hybrid materials have attracted much attention recently for their biocompatibility, tunable optical, and semiconducting properties. In this study, thin films fabricated using native DNA are modified to accommodate the assembled fluorescent dyes (perylene and 3‐bromoperylene), alongside the systematical evaluation of their photophysical properties and performance. Spectroscopy results reveal successful modulation of the molecular excitonic behaviour, achieve switchable single‐chromophore multi‐color emission in DNA‐surfactant‐dye thin films, with high optical transparency and thermal robustness. The nucleotide base pairs effectively suppress unfavorable intermolecular π–π stacking and aggregation (self‐association) of the chromophores, which prevents intersystem crossing and relaxation associated Rydberg type molecular clusters to form intermolecular excimers in E‐state (532, 513 nm) and Y‐state (489, 483 nm), blocking nonradiative decay. The preeminent emission observed (457, 445 nm) is attributed to the 0–1 band monomer emission. Compared to PMMA‐dye assembly, the thin film derived from DNA‐surfactant‐dye hybrid narrows the FWHM values up to 72%, displayed molarity ratio‐dependent emission color tunability from yellow‐orange (CIE 0.47, 0.34) to green (CIE 0.31, 0.21) and blue (CIE 0.17, 0.23). These findings provide a simple, all‐solution processed strategy for creating thin films using DNA‐surfactant‐dye hybrid materials with tunable optical properties suitable for biocompatible displays and data encryption.

Chameleon-like Photoluminescent Janus Nanoparticles as Full-Color Multicomponent Organic Nanoinks: Combination of Förster Resonance Energy Transfer and Photochromism for Encryption and Anticounterfeiting with Multilevel Authentication.

Increasing the security by the multilevel authentication mechanism was the most significant challenge in recent years for the development of anticounterfeiting inks based on photoluminescent nanomaterials. For this purpose, the greatest strategy is the use of multicomponent organic materials and a combination of Förster resonance energy transfer (FRET) with the intelligent behavior of photochromic compounds like spiropyran. Here, the hydroxyl-functionalized polymer nanoparticles were synthesized by emulsion copolymerization of methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA) in different compositions (0-30 wt % of HEMA). Results illustrated that the size of the nanoparticles changed from 64 to 204 nm, and a morphology evolution from spherical to Janus shape was observed by increasing the concentration of HEMA. Photoluminescent inks with red, green, and blue (RGB) fluorescence emissions were prepared by modification of nanoparticles containing 15 wt % of HEMA with spiropyran, fluorescein, and coumarin, respectively. To develop dual-color and multicolor photoluminescent inks that display static and dynamic emission, RGB latex samples were mixed together in different ratios and printed on cellulosic paper. Results display that the fluorescence emission of developed inks can be photoswitched between different statuses, including white to blue, green to blue, green to red/orange, purple to pink, and white to pink, utilizing the FRET phenomenon, photochromism, and a combination of both phenomena. Samples containing spiropyran displayed dynamic color changes in the emission to red, orange, and pink depending on the composition. Hence, developed dual-color and multicolor photoluminescent inks were used for printing of security tags and also painting of some hand-drawn artworks, which obtained results indicating high printability, maximum fluorescence intensity, high resolution, and fast responsivity upon UV-light irradiations of 254 nm (for static mode) and 365 nm (for dynamic mode). In addition, the multilevel authentication mechanism by a static emission under UV-light irradiation of 254 nm, a dynamic emission under UV-light irradiation of 365 nm, and photochromic color change was observed, resulting in increasing the security of developed inks. Actually, developed multicolor photoluminescent inks are the most efficient candidates for developing a new category of chameleon-like high-security anticounterfeiting inks that have tunable optical properties and complex multilevel authentication mechanisms.

Electrochemical synthesis of a novel hybrid nanocomposite based on Co3O4 nanoparticles embedded in PANI- camphor sulfonic Acid matrix for optoelectronic applications

In this study, we report on the preparation and characterization of Co3O4 nanoparticles (NPs) embedded in polyaniline-Camphor Sulfonic Acid (PANI-CSA) polymer matrix via electrochemical polymerization method. Developing conductive organic films with tunable optical properties are crucial for many novel optoelectronic applications. Thus, incorporation of metallic oxide nanoparticles (Co3O4 NPs) into polymer matrix (PANI-CSA) represents an alternative approach to address these desired features. As a result of careful optimization of several growth conditions, PANI-CSA/Co3O4 hybrid nanocomposites with high crystalline and homogeneous structures were successfully synthesized on ITO substrates. The impact of Co3O4 NPs concentrations on the structural and optical properties has been extensively investigated. A variety of structural and optical techniques, including FTIR, UV-VIS spectroscopy, and XRD, were employed to characterize the prepared hybrid nanocomposites. The initial findings and analysis reveal that the integration of Co3O4 NPs into PANI-CSA matrix have a trifunctional role in reducing π-polaron and Urbach energies (EU) whereas increasing π-π* band gaps. A further increase in NPs concentration up to 12 wt % results in continuous increase in the absorbance bands and absorption coefficients, indicating improved optical properties as compared to the control sample (PANI-CSA without NPs). The observed redshifts in absorbance band positions are attributed to narrowing of the optical band gap caused by interactions between PANI-CSA chains and Co3O4 NPs. FTIR spectra confirmed the exact chemical composition of PANI-CSA/Co3O4 nanocomposites, exhibiting broadened and less intense peaks compared to the control sample, indicating their interaction at the molecular levels. Additionally, XRD measurements indicate that no peaks of other phases were detected in all nanocomposites, demonstrating their purity and crystallinity. Finally, A single oscillator model by Wemple-DiDomenico (WDD) coupled with a Sellmeier dispersion relation based on one term has been utilized to model the typical electronic transition excitation energies, dispersion energies, optical conductivities, and many other optical desperation parameters for PANI-CSA and PANI-CSA/Co3O4 at various concentrations. For instance, in response to increased NPs content, linear optical susceptibility, third-order nonlinear optical susceptibility, and nonlinear refractive index decrease. In contrast, the ratio of free carriers to effective mass (N/m) increased from 4.73 × 1039 to 4.91 × 1039 m−3 kg−1 with increasing NPs concentration. Based on the observed results, these hybrid nanocomposites possess improved properties, indicating their potential use as active materials in a variety of novel optoelectronic applications.

Chiral Pearlescent Cellulose Nanocrystals Films with Broad-Range Tunable Optical Properties for Anti-Counterfeiting Applications.

Pearlescent materials are of technological importance in a diverse array of industries from cosmetics to premium paints; however, chiral pearlescent materials remain unexplored. Here, chiral pearlescent films with on-demand iridescence and metallic appearance are simply organized by leveraging vertical pressure to direct the self-assembly of cellulose nanocrystals. The films are formed with a bilayer planar anchored left-handed chiral nematic architecture, in which the bottom layer is featured with a vertical gradient pitch, and the top layer is featured with a uniform pitch. Simultaneous reflection of the rainbow colors and an on-demand color of left-handed polarized light with angle-dependent wavelength and polarization state accounts for the unique optical phenomenon based on experimental observation and theoretical analysis. Such chiroptical property can be readily tuned with architectural design, enabling reproducible optical appearance with high fidelity. Bringing the pearlescence, iridescence, and specular reflection together endows cellulose nanocrystal films with rich and tunable chiroptical properties that can be used for anti-counterfeiting applications. The current work marks the beginning of chiral pearlescent materials from renewable resources, while the pressure-directed self-assembly provides a step toward scalable production.

Two-dimensional GaP monolayer with tunable electrical and optical properties

The optical characteristics of two-dimensional (2D) monolayer formations in GaP. According to the predicted binding energies, the GaP monolayers are in constant contact. GaP monolayer was revealed to be semiconducting, with gaps of 2.080 eV. Furthermore, the predicted optical properties indicate that the GaP monolayer will absorb light at wavelengths ranging from infrared to ultraviolet. As a result, GaP monolayer should be appealing for visible-light communication and photocatalytic devices. It is possible to determine that this layer is kinematically stable by studying the form of the phonon, as all frequencies have positive values and there are no negative values for frequency. It is also worth noting that the frequency values exceed 1150 cm-1. Finally, the unexpectedly good properties of GaP monolayer are expected to be used in a variety of combinations in solar cells, field-effect transistors, catalysts, and optical devices.

An Open‐Source Multifunctional Testing Platform for Optical Phase Change Materials

Owing to their unique tunable optical properties, chalcogenide phase change materials are increasingly being investigated for optics and photonics applications. However, in situ characterization of their phase transition characteristics is a capability that remains inaccessible to many researchers. Herein, a multifunctional silicon microheater platform capable of in situ measurement of structural, kinetic, optical, and thermal properties of these materials is introduced. The platform can be fabricated leveraging industry‐standard silicon foundry manufacturing processes. This platform is fully open‐sourced, including complete hardware design and associated software codes.

Dramatically Enhanced Valley-Polarized Emission by Alloying and Electrical Tuning of Monolayer WTe2 x S2(1- x ) Alloys at Room Temperature with 1T'-WTe2 -Contact.

Monolayer ternary tellurides based on alloying different transition metal dichalcogenides (TMDs) can result in new two-dimensional (2D) materials ranging from semiconductors to metals and superconductors with tunable optical and electrical properties. Semiconducting WTe2 x S2(1- x ) monolayer possesses two inequivalent valleys in the Brillouin zone, each valley coupling selectively with circularly polarized light (CPL). The degree of valley polarization (DVP) under the excitation of CPL represents the purity of valley polarized photoluminescence (PL), a critical parameter for opto-valleytronic applications. Here, new strategies to efficiently tailor the valley-polarized PL from semiconducting monolayer WTe2 x S2(1- x ) at room temperature (RT) through alloying and back-gating are presented. The DVP at RT is found to increase drastically from < 5% in WS2 to 40% in WTe0.12 S1.88 by Te-alloying to enhance the spin-orbit coupling. Further enhancement and control of the DVP from 40% up to 75% is demonstrated by electrostatically doping the monolayer WTe0.12 S1.88 via metallic 1T'-WTe2 electrodes, where the use of 1T'-WTe2 substantially lowers the Schottky barrier height (SBH) and weakens the Fermi-level pinning of the electrical contacts. The demonstration of drastically enhanced DVP and electrical tunability in the valley-polarized emission from 1T'-WTe2 /WTe0.12 S1.88 heterostructures paves new pathways towards harnessing valley excitons in ultrathin valleytronic devices for RT applications.

Photoluminescence and photothermal conversion in boric acid derived carbon dots for targeted microbial theranostics

Theranostic carbon dots (CDs) have attracted widespread attention recently due to their tunable optical properties and diverse bioactivities. Beyond fluorescent imaging application, the photothermal property endows CDs with the potential for microbial inactivation. However, realization of the effective conversion between fluorescence and heat in one CD system has rarely been reported. Herein, we provide a simple strategy for targeted microbial theranostics based on 4-carboxyphenylboronic acid-derived CDs (PCBA-CDs) which possess concentration-dependent photoluminescence/photothermal features. At lower concentrations, PCBA-CDs show bright and stable fluorescent signals ranging from blue to green. The fluorescence intensity gradually decreases with increasing concentration, while on the contrary, the photothermal effect of PCBA-CDs ascends progressively due to the rearrangement of electronic transitions in aggregated CDs. PCBA-CDs also demonstrate high affinity to the polysaccharide structures on the surface of microbe which allows rapid microbial fluorescence imaging as well as specific photothermal ablation of pathogens in skin wounds using PCBA-CDs at lower and higher concentrations, respectively. This study supplies a facile nanotheranostic strategy for just-in-time microbial management using bioactive CDs.

Tunable electronic and optical properties of GeC/g-C3N4 vdWH by electric field and biaxial strain

van der Waals heterostructures (vdWHs) show great potential for optoelectronic devices and photocatalysis. This work investigates the stability, electronic structure and optical properties of GeC/g-C3N4 using first-principles and considers the role of external electric fields and biaxial strain in the heterostructure. The results show a reduced band gap of GeC/g-C3N4 vdWH with strong optical absorption in the visible light range compared to monolayer GeC and g-C3N4. The heterostructure is a type-II semiconductor that is extremely suitable for the development of optoelectronic devices and photocatalytic materials. The external electric field can flexibly tune the band gap and band alignment of GeC/g-C3N4 vdWH, enabling it to transition between type-I, type-II and type-III. Biaxial strain effectively tunes the band structure of GeC/g-C3N4 vdWH, reducing the band gap and further increasing optical absorption capacity. These results suggest that external electric fields and biaxial strain are effective ways to tune GeC/g-C3N4 vdWH, providing a theoretical basis for relevant experimental preparation.

Hot-injection synthesis of lead-free pseudo-alkali metal-based perovskite (TlSnX3) nanoparticles with tunable optical properties

The commercialization of organo-inorganic hybrid perovskite materials for optoelectronic applications is limited owing to the restriction of lead (Pb) usage in consumer electronics and the instability of organic cations in the perovskite structure. To address these challenges, we synthesize TlSnX3 (X = Cl, Br, and I) perovskite nanoparticles (NPs) with high crystallinity and uniformity using the hot-injection method. The optical properties of TlSnX3 NPs are fine-tuned by substituting the halide ions of TlSnX3. In addition, the oxidation of Sn in TlSnX3 NPs is effectively prevented by the strong reducing ligands such as dioleamide (DOA) and trioctylphosphine (TOP). Furthermore, TlSnX3 NPs-based perovskite solar cells (PSCs) are fabricated by a spin-coating method; they exhibited a high open-circuit voltage (∼1.4 V). These results demonstrate that TlSnX3 NPs can be an attractive candidate for solution-processable optoelectronic devices.

Carbon Dots -A Turn-On Probe for Neurological Disorder

The creation of novel methods is essential for the early diagnosis and treatment of neurological illnesses (NDs). The blood-brain barrier (BBB), which can prevent substances from accessing the central nervous system, is the most difficult obstacle to overcome in the development of neural medication delivery systems (CNS). For several biological applications, carbon dots (CDs) have emerged as highly outstanding and promising agents, including the treatment of brain tumours, ND, and bioimaging research. Because of their great qualities, they have a lot of potential for a range of scientific disciplines due to their biocompatibility, tiny size, tunable optical properties, photostability, and straightforward fabrication processes. This article's goal is to provide a summary of current CD research and to make recommendations for future work on creating neural drug delivery systems that can penetrate the BBB and reach the central nervous system. The two main subjects of this review are CD toxicity and unique optical properties. For a variety of neurological illnesses, a unique CD-based drug delivery system is designed in detail. This study also explores the possible applications of CDs for neurodegenerative disease therapies and imaging of brain tumours. The final section provides a summary of present CD sensing applications and projected future developments.

Adsorption and Molecular Display of a Redox-Active Protein on Gold Nanoparticle Surfaces.

Engineered gold nanoparticles (AuNPs) have great potential in many applications due to their tunable optical properties, facile synthesis, and surface functionalization via thiol chemistry. When exposed to a biological environment, NPs are coated with a protein corona that can alter the NPs' biological identity but can also affect the proteins' structures and functions. Protein disulfide isomerase (PDI) is an abundant protein responsible for the disulfide formation and isomerization that contribute to overall cell redox homeostasis and signaling. Given that AuNPs are widely employed in nanomedicine and PDI plays a functional role in various diseases, the interactions between oxidized (oPDI) and reduced (rPDI) with 50 nm citrate-coated AuNPs (AuNPs) are examined in this study using various techniques. Upon incubation, PDI adsorbs to the AuNP surface, which leads to a reduction in its enzymatic activity despite limited changes in secondary structures. Partial enzymatic digestion followed by mass spectrometry analysis shows that orientation of PDI on the NP surface is dependent on both its oxidation state and the PDI:AuNP incubation ratios.

Nanomatryoshka as a nano-material for use in laser-induced hyperthermia in biological tissues: A multiphysics-based computational modeling approach

The growing demand for efficient and biocompatible materials in laser-induced medical hyperthermia applications has led us to investigate a novel material known as the gold nanomatryoshka. This unique structure, composed of three superimposed layers (Au–SiO2–Au), offers significant advantages over conventional plasmonic structures, such as gold nanorods, due to its spherical geometry and potential for achieving the highest available density. In this study, our primary motivation is to explore the tunable optical absorption properties of the gold nanomatryoshka by adjusting the core radius and the thickness of its two outer layers (shells). By applying the Mie theory to calculate the interaction of light with gold nanomatryoshka, the absorption and scattering cross sections of these structures were obtained. Additionally, by employing the Monte Carlo method (photon transport within biological tissue) and combining with the bioheat equation (thermal analysis in the tissue), the temperature distribution inside the tissue was obtained. The key aim of our research is to establish a robust computational modeling methodology for assessing the size-dependent efficiency of the gold nanomatryoshka in medical hyperthermia applications. The tunability of its optical properties, enabled by its unique structure, holds immense promise for optimizing its performance in laser-based cancer treatments and other biomedical applications.Present study concludes with the successful demonstration of the gold nanomatryoshka's potential for enhancing the effectiveness of laser-based cancer treatment. Furthermore, its biocompatibility, attributed to the outer gold layer, makes it a compelling candidate for treatment, particularly in nanoparticle-based treatments of cancer within organs like the prostate. The significance of this research lies in its contributions to the design and implementation of the gold nanomatryoshka in medical hyperthermia applications. By addressing concerns related to core-shell structures (Au–SiO2), our findings pave the way for developing more effective and targeted therapeutic strategies, thus advancing the field of laser-induced medical hyperthermia and its applications in cancer treatment.

Bio‐inspired photonic crystals: Tailoring the dielectric building blocks to control the light propagation

AbstractPhotonic crystals have drawn tremendous attention in recent years owing to their unique optical properties and remarkable advantages in various applications such as bioassays, sensors and optical devices. Benefiting from the spatially ordered structures, the flow of visible light can be manipulated by photonic crystals in a controlled manner. In this review, we summarize recent progress toward bio‐inspired photonic crystals, including techniques for the construction of spatially ordered structures in diverse dimensions for photonic crystals, and strategies to manipulate the periodicity of the dielectric building blocks to control the light propagation in the presence of external stimuli. We start with the description of structure induced colors in nature with a systematic investigation to reveal the derivation of these colors, followed by a discussion on the design and fabrication of various types of bio‐inspired photonic crystals by manipulating the arrangement of dielectric building blocks. We also highlight the stimuli responsive photonic crystals with tunable optical properties and their applications in sensing and color display.

Targeted, Molecular Europium(III) Probes Enable Luminescence-Guided Surgery and 1 Photon Post-Surgical Luminescence Microscopy of Solid Tumors.

Discrete luminescent lanthanide complexes represent a potential alternative to organic chromophores due to their tunability of optical properties, insensitivity to photobleaching, and large pseudo-Stokes shifts. Previously, we demonstrated that the lack of depth penetration of UV excitation required to sensitize discrete terbium and europium complexes can be overcome using Cherenkov radiation emitted by clinically employed radioisotopes in situ. Here, we show that the second-generation europium complexes [Eu(III)(pcta-PEPA2)] and [Eu(III)(tacn-pic-PEPA2)] (Φ = 57% and 76%, respectively) lower the limit of detection (LoD) to 1 nmol in the presence of 10 μCi of Cherenkov emitting isotopes, 18F and 68Ga. Bifunctionalization provides access to cysteine-linked peptide conjugates with comparable brightness and LoD. The conjugate, [Eu(tacn-(pic-PSMA)-PEPA2)], displays high binding affinity to prostate-specific membrane antigen (PSMA)-expressing PC-3 prostate cancer cells in vitro and can be visualized in the membrane-bound state using confocal microscopy. Biodistribution studies with the [86Y][Y(III)(tacn-(pic-PSMA)-PEPA2)] analogue in a mouse xenograft model were employed to study pharmacokinetics. Systemic administration of the targeted Cherenkov emitter, [68Ga][Ga(III)(PSMA-617)], followed by intratumoral injection or topical application of 20 or 10 nmol [Eu(III)(tacn-(pic-PSMA)-PEPA2)], respectively, in live mice resulted in statistically significant signal enhancement using conventional small animal imaging (620 nm bandpass filter). Optical imaging informed successful tumor resection. Ex vivo imaging of the fixed tumor tissue with 1 and 2 photon excitation further reveals the accumulation of the administered Eu(III) complex in target tissues. This work represents a significant step toward the application of luminescent lanthanide complexes for optical imaging in a clinical setting.

Organothiol-directed synthesis and growth mechanism of Ag octahedra with tunable optical properties in aqueous solution

Shape-selective synthesis of Ag nanocrystals in the aqueous system remains a challenge, and insight into the mechanism of crystal growth is lacking. Here, we synthesized Ag octahedra (Ag Oh) with sharp corners and edges by the seed-mediated method in an aqueous solution at low temperatures (35 °C) and wide ranges of edge lengths (52–187 nm). l-cysteine directs the kinetic transformation of Ag cubes into octahedral nanocrystals of different sizes by selective deposition on the {100} plane. The thermodynamic product of the organothiol-directed synthesis was discovered to be truncated tetrahedra. The regrowth of octahedral nanocrystals in the absence of surfactant leads to corner deposition of Ag with the formation of concave Oh. Au@Ag tip-blobbed and concave Oh with tunable optical properties were synthesized using octahedral nanocrystals as a sacrificial template. Furthermore, by measuring the refractive index sensitivity and figure of merit (FOM) of Ag Oh, we have demonstrated its potential as a promising candidate for plasmonic sensors. The proposed concept of organothiol-directed deposition can be used to synthesize various nanocrystals with tunable properties as promising candidates for progress in optics, catalysis, and biomedicine applications.

The Tunable Electronic and Optical Properties of Two-Dimensional Bismuth Oxyhalides.

Two-dimensional (2D) bismuth oxyhalides (BiOX) have attracted much attention as potential optoelectronic materials. To explore their application diversity, we herewith systematically investigate the tunable properties of 2D BiOX using first-principles calculations. Their electronic and optical properties can be modulated by changing the number of monolayers, applying strain, and/or varying the halogen composition. The band gap shrinks monotonically and approaches the bulk value, the optical absorption coefficient increases, and the absorption spectrum redshifts as the layer number of 2D BiOX increases. The carrier transport property can be improved by applying tensile strain, and the ability of photocatalytic hydrogen evolution can be obtained by applying compressive strain. General strain engineering will be effective in linearly tuning the band gap of BiOX in a wide strain range. Strain, together with halogen composition variation, can tune the optical absorption spectrum to be on demand in the range from visible to ultraviolet. This suggests that 2D BiOX materials can potentially serve as tunable novel photodetectors, can be used to improve clean energy techniques, and have potential in the field of flexible optoelectronics.

α-Quartz Phase Stabilization, Surface Texturing, and Tunable Optical Properties of Nanocrystalline GeO2 Films Made by Pulsed-Laser Deposition: Implications for Optical and Optoelectronic Applications

α-Quartz Phase Stabilization, Surface Texturing, and Tunable Optical Properties of Nanocrystalline GeO₂ Films Made by Pulsed-Laser Deposition: Implications for Optical and Optoelectronic Applications

Tunable Optical Properties and the Role of Defects on the Carrier Lifetimes of Cs3Sb2I9 Synthesized in Various Solvents

Pb‐free halide perovskites have recently attracted immense attention due to the number of advantages in their optical and electronic properties. However, tuning the optical bandgap with minimized amounts of point defects is a particularly challenging task in photovoltaics. It is pivotal to clearly understand the detailed relationship between the bandgap change with defect generation and charge carrier lifetime. In this study, Cs3Sb2I9 crystals are synthesized by varied choice of solvents, namely, γ‐butyrolactone, a mixture of dimethylformamide and dimethyl sulfoxide, and hydroiodic acid. Although the same principles of decreasing solubility and crystallization are applied, Cs3Sb2I9 crystals with different size and shape in microscopic and macroscopic scale are obtained during heating and cooling of the solution. The synthesized crystals are investigated using a combination of different spectroscopies including Raman, UV–visible, and time‐resolved photoluminescence. In the results, it is suggested that there is a strong relationship between Urbach energy and the lifetime of charge carriers. In this research, readily applicable practical principles and examples of how to control the defects for the advancement in Pb‐free perovskite photovoltaics are provided.