Formation Of Self-trapped Excitons Research Articles

Self-Trapped Excitons in Metal-Halide Perovskites Investigated by Time-Dependent Density Functional Theory.

We present a theoretical study of the formation of self-trapped excitons (STEs) and the associated broadband emission in metal-halide perovskites Cs4SnBr6 and Cs2AgInCl6, using time-dependent density functional theory (TDDFT) with the dielectric-dependent hybrid (DDH) functional. Our approach allows for an accurate description of the excitonic effect and geometry relaxation in the electronic excited states and yields optical gap, STE emission energy, and emission spectra in reasonable agreement with experiments. We point out the significance of considering geometry relaxations in the electronic excited state by showing that the exciton-phonon coupling computed in the ground-state atomic geometry is insufficient to describe the physical properties of STEs. Overall, we find that TDDFT with the DDH hybrid functional is a suitable approach for the study of the formation of STEs in perovskite and provides insights for designing metal-halide perovskites with tailored emission properties.

Ligand-Induced Chirality in ClMBA2 SnI4 2D Perovskite.

Chiral perovskites possess a huge applicative potential in several areas of optoelectronics and spintronics. The development of novel lead-free perovskites with tunable properties is a key topic of current research. Herein, we report a novel lead-free chiral perovskite, namely (R/S-)ClMBA2 SnI4 (ClMBA=1-(4-chlorophenyl)ethanamine) and the corresponding racemic system. ClMBA2 SnI4 samples exhibit a low band gap (2.12 eV) together with broad emission extending in the red region of the spectrum (∼1.7 eV). Chirality transfer from the organic ligand induces chiroptical activity in the 465-530 nm range. Density functional theory calculations show a Rashba type band splitting for the chiral samples and no band splitting for the racemic isomer. Self-trapped exciton formation is at the origin of the large Stokes shift in the emission. Careful correlation with analogous lead and lead-free 2D chiral perovskites confirms the role of the symmetry-breaking distortions in the inorganic layers associated with the ligands as the source of the observed chiroptical properties providing also preliminary structure-property correlation in 2D chiral perovskites.

Unusual Pressure-Induced Self-Trapped Exciton to Free Exciton Transfer in Chiral 2D Lead Bromide Perovskites.

The phenomenon of pressure-induced emission alterations related to complex excitonic dynamics in 2D lead halide perovskites (LHPs) has gained considerable attention for understanding their structure-property relationship and obtaining inaccessible luminescence under ambient conditions. However, the well-known pressure-induced emissions are limited to the formation of self-trapped excitons (STEs) due to the structural distortion under compression, which goes against the advantage of the highly pure emission of LHPs. Here, the pressure-induced detrapping from STEs to free excitons (FEs) accompanied by the dramatic transition from broadband orangish emission to narrow blue emission has been achieved in chiral 2D LHPs and R- and S-[4MeOPEA]2PbBr4, (4MeOPEA = 4-methoxy-α-methylbenzylammonium). The combined experimental and calculated results reveal that the distortion level of PbBr6 octahedra of R- and S-[4MeOPEA]2PbBr4 exhibits an unusually significant reduction as the applied pressure increases, which leads to decreased electron-phonon coupling and self-trapped energy barrier and consequently enables the detrapping of STEs to FEs. This work illustrates the dramatic exciton transfer in 2D LHPs and highlights the potential for realizing highly efficient and pure light emissions by manipulating the structural distortion via strain engineering.

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.

Sb3+-Doped Indium-Based Metal Halide (Gua)3InCl6 with Efficient Yellow Emission.

In recent years, low-dimensional organic-inorganic hybrid metal halides (OIHMHs) have shown excellent photophysical properties due to their quantum structure, adjustable energy levels, and energy transfer between inorganic and organic components, which have attracted extensive attention from researchers. Herein, we synthesize a zero-dimensional (0D) OIHMH, Sb3+:(Gua)3InCl6, by introducing Sb3+ into (Gua)3InCl6, which undergoes a significant enhancement of the emission peak at 580 nm with the photoluminescence quantum yield (PLQY) boosted from 17.86 to 95.72% when excited at 340 nm. This boost in photoluminescence of the doped sample was studied by combining ultrafast femtosecond transient absorption, temperature-dependent photoluminescence (PL) spectra, and density functional theory (DFT) calculation, revealing the process of self-trapped exciton (STE) recombination to emit light at both Sb and In sites in this 0D structure simultaneously. This material with the lowest dark STE level at the In site for emission in the undoped sample can amazingly yield very strong emission in the doped sample, which has never been observed before. Finally, we tested its application in a photoelectric device. This work not only helps to gain a deeper understanding of the formation of STEs in In-based halides but also plays a certain guiding role in the design of new luminescent materials.

Unlocking structural and photoelectric properties of lead-free double perovskites at high temperature

The lead-free double perovskite, increasingly sought for optoelectronic pursuits, is distinguished by its notable stability, optical properties, and non-toxic characteristic. An extensive inquiry into the structural and photoelectric properties of Cs2NaBiCl6 at heightened temperatures was undertaken using experimental evaluations and theoretical computations. The compound Cs2NaBiCl6, synthesized using a hydrothermal technique, was confirmed via various analytical methods. Advanced techniques such as high-temperature X-ray diffraction, X-ray fluorescence, X-ray photoelectron spectroscopy, and selected area electron diffraction were employed for the investigation of its crystal structure. Further investigation of microstructure was undertaken using electron microscopes. High-temperature luminescence stability disclosed a high exciton binding energy of 326 meV. The Huang-Rhys factor (6.4) denotes a robust electron-phonon coupling effect and facile formation of self-trapped excitons (700 nm). Applied first principles render valuable insight into structural and photoelectric nuances, notably at escalated temperatures. Cs2NaBiCl6 as an indirect bandgap semiconductor and details the experimental and theoretical bandgap, which exhibits an increasing trend before subsequently declining at elevated temperatures. These results strongly support the material's high-temperature stability, emphasizing its applicability in applications such as rare-earth-doped phosphors. The dynamic stability of the material, evidenced by its mechanical performance, further underscores its potential for application in photoelectric devices.

Regulating Exciton De-Trapping of Te4+ -Doped Zero-Dimensional Scandium-Halide Perovskite for Fluorescence Thermometry with Record High Time-Resolved Thermal Sensitivity.

Fluorescence thermometry has been propelled to the forefront of scientific attention due to its high spatial resolution and remote non-invasive detection. However, recent generations of thermometers still suffer from limited thermal sensitivity (Sr ) below 10% change per Kelvin. Herein, this work presents an ideal temperature-responsive fluorescence material through Te4+ -doped 0D Cs2 ScCl5 ·H2 O, in which isolated polyhedrons endow highly localized electronic structures, and the strong electron-phonon coupling facilitates the formation of self-trapped excitons (STEs). With rising temperature, the dramatic asymmetric expansion of the soft lattice induces increased defects, strong exciton-phonon coupling, and low thermal activation energy, which evokes a rapid de-trapping process of STEs, enabling several orders of magnitude changes in the fluorescence lifetime over a narrow temperature range. After regulating the de-trapping process with different Te4+ doping, a record-high Sr (27.36% K-1 ) of fluorescence lifetime-based detection is achieved at 325 K. The robust stability against multiple heating/cooling cycles and long-term measurements enables a low temperature uncertainty of 0.067 K. Further, the developed thermometers are demonstrated for the remote local monitoring of operating temperature on internal electronic components. It is believed that this work constitutes a solid step towards building the next generation of ultrasensitive thermometers based on low-dimensional metal halides.

Chiral induction and Sb3+ doping in indium halides to trigger second harmonic generation and circularly polarized luminescence

Recently, organic-inorganic hybrid metal halides (HMHs) have attracted extensive attention as promising multifunctional materials by virtue of their structural diversity and tunable photophysical properties. However, it remains a challenge to design HMHs with specific functions on demand. Herein, by introducing R/S-methylbenzylamine (R/S-MBA) and doping Sb3+, we have achieved both second harmonic generation (SHG) and circularly polarized luminescence (CPL) properties in lead-free indium halides. The introduction of chiral organic cations can break the symmetry and induce the indium halides to crystallize in the chiral space group. The Sb3+ with ns2 electronic configuration can serve as the dopants to promote the formation of self-trapped excitons, so as to activate highly efficient luminescence. As a result, the as-prepared Sb3+ doped (R/S-MBA)3InCl6 show not only SHG responses but also CPL signals with luminescence dissymmetry factor of −5.3 × 10−3 and 4.7 × 10−3. This work provides a new inspiration for the exploitation of chiral multifunctional materials.

Machine Learning Accelerated Prediction of Self‐Trapped Excitons in Double Halide Perovskites

Broadband emission induced by self‐trapped excitons (STEs) in double halide perovskites (DHPs) has received continuous attention in recent years. However, the comprehensive understanding of the STEs formation mechanism is still in its early stage. The corresponding roles of different B‐site cations also remain unclear in these advanced materials. The lack of an effective STEs database for DHPs hinders the efficient discovery of potential optoelectronic materials with strong STEs. Herein, a systematic STEs database is built for DHPs through density functional theory (DFT) calculations and proposed a highly efficient predictive machine learning (ML) model of the Huang–Rhys factor S for the first time. Results reveal the different contributions of two B‐site metal cations to the formation of STEs in DHPs, which helps to understand the in‐depth nature of STEs. Based on the accurate predictions of the effective phonon frequency ω , it is further realized that the prediction of S without conducting the time‐consuming phonon property calculations of DHPs offers new opportunities for exploring the STEs. Combining DFT calculations and ML techniques, this study supplies an effective approach to efficiently discover the potential novel optoelectronic materials, which provides important guidance for the future exploration of promising solid‐state phosphors.

Origin of Broad Emission Induced by Rigid Aromatic Ditopic Cations in Low-Dimensional Metal Halide Perovskites.

The development of broadband emitters based on metal halide perovskites (MHPs) requires the elucidation of structure-emission property correlations. Herein, we report a combined experimental and theoretical study on a series of novel low-dimensional lead chloride perovskites, including ditopic aromatic cations. Synthesized lead chloride perovskites and their bromide analogues show both narrow and broad photoluminescence emission properties as a function of their cation and halide nature. Structural analysis shows a correlation between the rigidity of the ditopic cations and the lead halide octahedral distortions. Density functional theory calculations reveal, in turn, the pivotal role of octahedral distortions in the formation of self-trapped excitons, which are responsible for the insurgence of broad emission and large Stokes shifts together with a contribution of halide vacancies. For the considered MHP series, the use of conventional octahedral distortion parameters allows us to nicely describe the trend of emission properties, thus providing a solid guide for further materials design.

Role of CsMnCl3 Nanocrystal Structure on Its Luminescence Properties

Cesium manganese chloride (CsMnCl3) nanocrystals (NCs) have recently been recognized as potential lead-free perovskite candidates for red emission. To ascertain how the luminescence properties depend on the NC structures formed under different synthesis conditions, we synthesized CsMnCl3 NCs in two polymorphic structures, namely, cubic (c-CsMnCl3) and rhombohedral (r-CsMnCl3), by tuning the reaction temperature of a hot injection route. c-CsMnCl3 NCs are found to be nonemissive, whereas r-CsMnCl3 NCs exhibit red emission at 670 nm with a photoluminescence quantum yield of 40%. Density functional theory calculations reveal an indirect band gap for c-CsMnCl3─the electronic transitions between valence and conduction band edges are prohibited by orbital symmetry and spin. Conversely, r-CsMnCl3 NCs possess a direct band gap. Further, transient absorption measurements suggest self-trapped exciton formation in r-CsMnCl3 NCs, which contributes to their emission characteristics. Our proof-of-concept demonstration of photocurrent generated from the emitting r-CsMnCl3 NCs indicates their suitability for luminescent solar concentrator applications. The findings of this work highlight the importance of understanding structure-luminescence relationship of emerging lead-free perovskites providing design criteria for red-emitting materials.

Investigation of self-trapped excitonic dynamics in hematite nanoforms through non-degenerate pump–probe transmission spectroscopy

Non-degenerate pump–probe transmission spectroscopy is used to examine the ultrafast dynamics of photo-excited carriers in hematite nanoforms at various pump fluences. Using coupled rate equations, the kinetics of self-trapped exciton (STE) formation and its interaction with free excitons resulting in exciton annihilation were studied. It is shown from this model that the majority of the excitons were trapped by polaronic trap states to form self-trapped excitons within ∼3.5 ps. The findings indicate that free excitons and STEs interact non-linearly, similar to trap-assisted bi-molecular Auger recombination to annihilate one another. It is observed that there is substantial dependence of kinetics of STE formation and exciton decay on photo-excited exciton density, and the nature of this dependence indicates the reduced screening of electron–phonon interaction. Using the screening model applied to the rate constants of STE formation and decay, we estimate the saturation exciton density to be ∼3.3 × 1017 cm−3 and the average STE density to be ∼3.8 × 1018 cm−3 in the hematite nanoforms. We also noticed that doping K and Ni to hematite nanoforms up to 5% did not remarkably change the nature of the exciton dynamics.

Deciphering competing radiative relaxation pathways observed in Pr3+-Activated yttrium-based compounds: UV emission versus visible emission

Pr3+-activated yttrium-based compounds have garnered significant research interest as the electronic transition of Pr3+ dopant incorporated in host lattices are quite versatile, giving rise to the production of either UV or visible electromagnetic radiation. The tunable 5d orbital energy level of Pr3+ with an electronic configuration [Xe]4f15d1 depending on the external crystal fields, coordinating anion ligands (mainly determined by covalency of anion ligands), and symmetry of crystal structures can indeed control the radiative decay processes whether to generate UV or self-trapped exciton-mediated visible emission. We have investigated three different Pr3+-activated crystals of YPO4, YBO3, and Y2SiO5 using two different excitation processes including direct host lattice excitation (cathodoluminescence: CL) and f-d excitation of Pr3+ dopants (photoluminescence: PL). Such radiative decay mechanism observed in Pr3+-doped yttrium-based compounds has been deciphered that photoexcitation of Pr3+ ions results in 4f15d1→4f2 electronic transition with UV emission (PL) whereas above-bandgap excitation of host lattices brings about the efficient production of visible emission mediated through self-trapped excitons (CL). When changing the anion sublattices, the emission peak corresponding to 4f15d1→4f2 transition shifted to longer wavelength as a result of modulated covalency and crystal field strength. As the host lattices changes as a function of anion sublattices, the bandgap reduced from 8.6 eV (for YPO4) to 7.6 eV (for YBO3) and to 6.1 eV (for Y2SiO5), directly influencing rate of trapping of exciton and their formation of self-trapped exciton, which further give rise to production of the self-trapped exciton mediated visible emission. The fundamental understanding of the multiple, radiative relaxation pathways provides a designing principle for achieving more efficient UV emitting phosphors (at the same time by suppressing visible emission or vice versa) for germicidal and medical applications.

Bimolecular Self-Trapped Exciton Formation in Bismuth Vanadate.

Bismuth vanadate (BiVO4) is a promising photoanode material for solar-driven water splitting, and knowledge of the photocarrier dynamics in BiVO4 could offer guidance to propel the development of the photoanode performance. Herein, we uncovered the nature of various photogenerated transient species in BiVO4 and extracted their respective dynamics. We found spectral and dynamic evidence that the electrons in the conduction band collapsed into severely localized small electron polarons on a subpicosecond time scale, while the holes in the valence band remained delocalized and accounted for the photoconductivity. In the following tens to hundreds of picoseconds, the electron polaron captured the hole to form a self-trapped exciton via a bimolecular reaction mechanism, and in consequence, the hole was immobilized. Our finding suggests that exciton dissociation strategies should be taken into account in the design of the BiVO4-based water-splitting applications in order to enhance charge transport and suppress charge recombination.

Highly stable vacancy-ordered double perovskite Rb2ZrCl6 with broadband emission for down-conversion white light-emitting diodes

In recent years, the lead-halide perovskite materials have shown great potential in lighting fields due to their excellent photoelectric properties. However, lead toxicity and instability severely limit their practical application and commercial development. In this work, zero-dimensional vacancy-ordered double perovskite Rb2ZrCl6 microcrystal was synthesized by hydrothermal method for the first time. The Rb2ZrCl6 microcrystals exhibit a blue-white light emission with high photoluminescence quantum yield of 60% and a large Stokes shift. The Rb2ZrCl6 has a high exciton binding energy and a strong electron-phonon coupling, which supports the formation of self-trapped excitons under light excitation and the generation of broadband emission. In addition, the Rb2ZrCl6 microcrystals show a remarkable stability against heat, ultraviolet light and environmental water/oxygen. Afterwards, we used the Rb2ZrCl6 microcrystals as the phosphors to fabricate a white light-emitting diode (WLED). The device demonstrates a color coordinate of (0.30, 0.32), a high color rendering of 90.0, and a good working stability, with no emission degradation over continuous 10 h operation. Together with the eco-friendly features and low-cost solution processability, the nontoxic Rb2ZrCl6 can therefore be deemed as a reliable light emitter for high-performance WLEDs.

Effect of self-trapped excitons in the optical properties of manganese-alloyed hexagonal-phased metal halide perovskite

Emission induced by self-trapped excitons (STEs) has recently been studied in several metal halide perovskites (MHPs), particularly in low-dimensional MHPs. STEs generally occur in low-dimensional MHPs owing to their soft lattices, strong electron–phonon coupling, and lattice distortion. However, the formation of STEs in all-inorganic high-dimensional MHPs, specifically in hexagonal phases, is challenging. From this perspective, we studied the formation of STEs in all-inorganic hexagonal-phase CsCdCl3 MHPs and further investigated the role of free excitons and STEs in the optical properties of CsCd(1-x)MnxCl3 MHPs. Mn2+ ion-activated CsCd(1-x)MnxCl3 MHPs were synthesized, and their crystal structures were refined. The CsCd(1-x)MnxCl3 MHPs exhibited orange emission upon 295 nm excitation with a high photoluminescence quantum yield of 74 %. Moreover, CsCd(1-x)MnxCl3 MHPs exhibited good thermal and chemical stability. We also investigated the effect of Mn2+ doping on CsCd(1-x)MnxCl3 single crystals, polycrystals, and nanocrystals. This work offers deep insights into the photophysical properties of MHPs as well as provides a promising approach to achieving high-quality, thermally, and chemically stable white-light emission.

H2O-NH4+-Induced Emission Modulation in Sb3+-Doped (NH4)2InCl5·H2O.

Lead-based metal halide perovskites have received widespread attention for their promising application prospects in the field of lighting and display due to their excellent optical properties. However, the toxicity of lead may hinder their further commercial application. Herein, a zero-dimensional (0D) metal halide (NH4)2InCl5·H2O with an orthorhombic structure and the Pnma space group was produced. With doping with Sb3+, these products exhibit one highly efficient and wide yellow emission band (∼450-850 nm) in their photoluminescence (PL) spectra, which covers almost the entire visible spectral range at room temperature; however, they give two emission bands with long decay lifetimes (microseconds) at low temperature. Temperature-dependent steady-state PL, transient PL spectroscopy, temperature-dependent Raman spectra characterization, and theoretical band structure calculations confirm that the dual-band emission at low temperature originates from the dual vibronic levels of the self-trapped exciton (STE) in the hole-vibration state, whose vibration energy is related to the H2O-NH4+ connection in the valence band. This result proves that the vibronic state in STE formation involves both electrons and holes in the excited states, the opposite of this happens in the electron-vibration band in most perovskite halides. These results provide new insight into the luminescent mechanism of Sb3+ in halide perovskites, especially used for emission color modulation by the temperature-dependent electron- or hole-vibration processes.

Highly Efficient and Ultra‐Broadband Yellow Emission of Lead‐Free Antimony Halide toward White Light‐Emitting Diodes and Visible Light Communication

AbstractDue to the broadband emission induced by self‐trapped excitons (STEs), low‐dimensional hybrid lead halides are regarded as an emerging class of highly efficient light emitters. However, the toxic lead element impedes their commercial application. Here, a new air‐stable hybrid lead‐free metal halide [Na(DMSO)2]3SbBr6 with a 0D structure constituted by [SbBr6] octahedral and [Na(DMSO)2]3 units is synthesized at room temperature, which exhibits a high photoluminescence quantum yield of 60% and an ultra‐broadband yellow emission centered at 608 nm, with a full width at half‐maximum of 160 nm. First‐principles calculations and experimental studies unveil that the formation of STEs in this 0D structure contributes the broad emission. Then, warm white light‐emitting diodes (WLEDs) are proposed by combining blue LED chips with yellow [Na(DMSO)2]3SbBr6, showing a color rendering index of 85, a correlated color temperature of 3603 K. Finally, the prepared WLEDs are utilized in visible light communication (VLC) with an achieved −3 dB bandwidth of 7.2 MHz and a high transmitted data rate of 81.6 Mbps by applying orthogonal frequency division multiplexing modulation with adaptive bit loading. This research not only enriches the family of perovskite related materials, but also inspires the potential of low‐dimensional metal halide in VLC.

A heterovalent doping strategy induced efficient cyan emission in Sb3+-doped CsCdCl3 perovskite microcrystal for solid state lighting

Metal halides can produce a broadband emission spectrum of self-trapped excitons (STEs) with a large stokes shift because they have strong electron-phonon coupling and soft lattice. In this study, CsCdCl3:xSb3+ perovskite microcrystals were prepared using a simple co-precipitation strategy at room-temperature. Their composition, morphology and phase structure were characterized by EDS, XPS, SEM and XRD. The result showed that the structure of the CsCdCl3:xSb3+ perovskite microcrystals was hexagonal. In terms of luminescence, the un-doped CsCdCl3 sample showed a quite broadband emission from the host STEs with a large Stokes shift of 340 nm. The PLE and PL of the CsCdCl3:0.007Sb3+ sample show two absorptions at the wavelength of 300 and 355 nm, which is because of the 1S0 → 1P1 and 1S0 → 3P1 transitions of Sb3+ ions and the enhanced cyan emission from STEs emission of [SbCl6] octahedra induced by a heterovalent doping strategy, respectively. In addition, in the PL spectra, there are two luminescence centers in the CsCdCl3:xSb3+ samples. The emission peak at 500 nm is higher than that at 600 nm, which can be attributed to the STEs of [SbCl6] and the two face-sharing octahedra [Sb2Cl9], respectively. The formation of STEs can be demonstrated by the large S value. The CsCdCl3:xSb3+ samples undergo two thermal processes, with an activation energy of 127 meV (Ea2) at a high temperature and 101 meV (Ea1) at a low temperature. Finally, they have good thermal and anti-water stability, and thus can be possibly applied in white LED with CIE color coordinates of 0.4119 and 0.3897, the CCT of 3227 K and CRI of 79.3.

Brillouin Light Scattering of Halide Double Perovskite

Cs2Ag1−x Na x In1−y Bi y Cl6 with high photoluminescence quantum yield (PLQY) and broadband emission due to self‐trapped excitons (STEs) is one of the promising candidates for single‐emitter‐based white light–emitting materials and devices. Considering fundamental physical mechanisms, structure design and performance optimization of devices, comprehensive knowledge of the elasticity, and thermal properties are imperative to understand the formation of STEs in Cs2Ag1−x Na x In1−y Bi y Cl6 and minimize thermomechanical stresses induced device failure, respectively. However, its elastic and thermal properties are still poorly understood. Herein, the first angle‐resolved Brillouin light scattering (BLS) measurements study for a bulk Cs2Ag0.4Na0.6InCl6:0.04%Bi3+ crystal is reported, and the first‐principles calculations of phonon dispersions are used to further validate our experimental results. Using the measured Brillouin frequency shifts, we evaluate the low elasticity of Cs2Ag0.4Na0.6InCl6:0.04%Bi3+: C 11 = 38.63, C 12 = 16.11, and C 44 = 10.20 GPa, which supports the thesis that STEs exist in semiconductors with excitons and a soft lattice. Additionally, an ultralow‐acoustic Debye temperature (87 K) and lattice thermal conductivity (1.03 W m−1 K−1) along the [111] direction of Cs2Ag0.4Na0.6InCl6:0.04%Bi3+, which indicates the weak interatomic interactions and elasticity are estimated. Furthermore, a general approach is also provided to investigate the elastic and thermal properties of materials with different crystal structures utilizing angle‐resolved BLS spectroscopy.