Photoluminescence Excitation Research Articles

Anomalous excitation wavelength dependent photoluminescence of Sb3+/Bi3+ co-doped double perovskites

Lead-free double perovskites have recently attracted lots of research interest due to their enhanced structural stability and decreased toxicity compared to lead-halide perovskites. However, origins of the dual emissions observed in photoluminescence (PL) are still controversial. Herein, PL properties of Sb/Bi co-doped Cs2NaInCl6 microcrystals are investigated. When the excitation wavelength is about 320–360 nm, the emission peak mainly locates at 450 nm. While excited at 250 nm, the emission peak reversely increases to ∼580 nm. According to Stokes shift, bandwidth, PL excitation spectra, PL lifetime, and temperature dependent PL, the 450 and 580 nm emissions are attributed to recombination of free exciton (FE) and self-trapped exciton (STE), respectively. Only when the excitation photon energy is large enough to generate lattice distortion and create excitons simultaneously does the STE form, exhibiting emission at 580 nm. As excitation wavelength increases, the photon energy becomes insufficient for the formation of the STE but is able to create FEs. Thus, the emission is dominated by FE recombination. Therefore, the excitation wavelength dependent PL peak position is observed. Moreover, we demonstrate an anti-counterfeiting pattern with excitation wavelength dependent color, which cannot be imitated by other luminescent materials, implying an improved security.

Broadening mechanisms of donor-bound exciton photoluminescence in Ga-doped ZnO nanowires

Donor spins in ZnO NWs have promise for quantum information (QI) applications due to high crystalline quality, narrow excitonic luminescence linewidths, and a direct bandgap of this material. It is important to understand the processes that can lead to inhomogeneous broadening of the excitonic transitions for realization of QI devices. We investigate the effect of Ga dopant concentration on the low temperature photoluminescence (PL) of Ga-doped ZnO nanowires. Spectrometer-resolution-limited donor-bound exciton (D0X) PL lines are observed at low concentrations with linewidths of around 0.1 meV. A clear increase in the Ga D0X line is observed as trace amounts of Ga are added. Above a certain concentration threshold, we observe a strong increase in the lateral growth coupled with a significant tail on the low energy side of the D0X emission, which scales linearly with dopant precursor concentration. We have analyzed this behavior using different models, including a model based on a bound exciton wavefunction overlap with neigbhouring donors and a Stark effect model due to random charged impurities. We rule out both of these models based on PL excitation spectroscopy measurements and show that a simple exponential model of the Urbach form gives the best fit and points to disorder in the more heavily doped shells.

The role of the dopant in the electronic structure of erbium-doped TiO2 for quantum emitters

Erbium-doped TiO2 materials are promising candidates for advancing quantum technologies, necessitating a thorough understanding of their electronic and crystal structures to tailor their properties and enhance coherence times. This study explored epitaxial erbium-doped rutile TiO2 films deposited on r-sapphire substrates using molecular beam epitaxy. Photoluminescence excitation spectroscopy demonstrated decreasing photoluminescence lifetimes with erbium doping, indicating limited optical coherence times. Lattice distortions associated with Er3+ were probed by x-ray absorption spectroscopy, indicating that erbium primarily occupies Ti4+ sites and influences oxygen vacancies. Significant lattice distortions in the higher-order shells and apparent full coordination around erbium suggest that additional defects are likely prevalent in these regions. These findings indicate that defects contribute to limited coherence times by introducing alternative decay pathways, leading to shorter photoluminescence lifetimes.

Optical and EPR study of Mn4+ ions in different crystal environments in Mn, Li co-doped MgO

The influence of Li ion on the symmetry of Mn4+ center and its photoluminescence (PL) in MgO:0,01%Mn, 3% Li ceramics is studied by the X-ray diffraction, electron paramagnetic resonance (EPR), PL and optical absorption methods. It is shown that Li co-doping stimulates conversion of Mn2+ on Mg site into Mn4+ and can decrease symmetry of Mn4+ in a case of their specific close arrangement in the crystal lattice. Two kinds of Mn4+ centers are identified in the EPR and PL spectra: cubic Mn4+ and tetragonal complex Mn4+-Li+. The parameters of corresponding EPR centers are estimated from the experimental spectra (gcub=1.994, |A|cub=70.9x104 cm-1; g1tetr=g2tetr=1.994, g3tetr=1.993, |A|tetr=71x104 cm-1, |D|tetr=220x104 cm-1). The PL lines observed in the low temperature PL spectra are assigned to the specific Mn4+ related centers by using a complementary study of PL excitation spectra and temperature dependent PL spectra. The lines at 654 nm and 671 nm are ascribed to R-line of Mn4+ in a site of cubic symmetry and its phonon overtone, correspondingly, as well as the lines at 666 nm and 681 nm are attributed to R2 line of Mn4+ in site with tetragonal symmetry and to its phonon overtone, correspondingly. It is shown that in Mn doped MgO ceramics made without intentional Li co-doping, the cubic Mn4+ center can be present and contribute to the PL spectra.

Synthesis and luminescence properties of Ca2AlNbO6:Fe3+ phosphor for plant growth lighting

With the development of plant growth lighting, more and more attention has been paid to red and far red luminescent materials. In this work, we synthesize successfully a non-rare earth and non-toxic Ca2AlNbO6:Fe3+ phosphor in air and investigate the crystal structure, morphology, and luminescence properties of Ca2AlNbO6:Fe3+ by using powder X-Ray Diffraction, the field emission scanning electron microscopy, and the Edinburgh steady-state FS5 spectrometer, respectively. The far-red emission with peak at 714 nm of Ca2AlNbO6:Fe3+ is due to the 4T1(4G) → 6A1(6S) transition of Fe3+ ion. Photoluminescence excitation (PLE) spectrum of Ca2AlNbO6:Fe3+ includes four PLE peaks, which are assigned to the O2− → Fe3+ charge transfer band (CTB) (309 nm), the 6A1(6S) → 4T1(4P) (364 nm), 6A1(6S) → 4E(4D) (395 nm), and 6A1(6S) → 4T2(4G) (532 nm) transitions of Fe3+, respectively. We further study the concentration/temperature dependent emission spectra and time-resolved emission spectra. The optimal Fe3+ doping concentration (0.6mol%) and the only luminous center (Fe3+) in Ca2AlNbO6:Fe3+ are confirmed. The decay curves of Ca2AlNbO6:xFe3+ (0.2 mol% ≤ x ≤ 1.2 mol%) are measured and their lifetimes decrease from 463.24 to 385.29 μs＀ The emission spectra under different temperatures prove that Ca2AlNbO6:Fe3+ has a good heat stability. We explain the luminous mechanism and concentration/thermal quenching mechanisms, and further research the application prospect of Ca2AlNbO6:Fe3+ in plant growth lighting.

Preparation and Characterization of Red, Green, Blue (RGB) and White Luminescent Inorganic/Organic Polymers Through In Situ Polymerization.

YVO4:Eu3+/PMMA, LaPO4:Ce3+,Tb3+/PMMA and CaWO4/PMMA nanocomposites were prepared by in situ polymerization method with hydrophobic YVO4:Eu3+, LaPO4:Ce3+,Tb3+ and CaWO4 nanoparticles as the filler and poly (methyl methacrylate) (PMMA) as the host material. All the nanoparticles and composites have been well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), the thermogravimetric analysis (TGA), photoluminescence excitation, and emission spectra and luminescence decays. YVO4:Eu3+/PMMA, LaPO4:Ce3+,Tb3+/PMMA, CaWO4/PMMA nanocomposites exhibit strong red, green and blue photoluminescence upon 254nm UV excitation, respectively. The yellow and white LED nanocomposites with CIE coordinates of (0.411, 0.498) and (0.334, 0.359) were obtained by triply integrating the red, green and blue nanoparticles into PMMA. Thanks to the abundant luminescent colors from RGB to yellow and white in these polymer composites under UV excitation, they can be potentially used in various optoelectronic fields.

Combustion Synthesis and Influence of Dy3+ ions on Structural and Photometric Attributes of Olivine-type LiMgPO4 Nanophosphors for Illumination Applications.

The low-cost technique of combustion synthesis was used to synthesize the trivalent Dysprosium (Dy3+) doped olivine type Lithium Magnesium Phosphate (LiMgPO4). X-ray diffraction (XRD) analysis verified the orthorhombic phase, corresponding to the space group Pnma. The crystallite size of 50.83nm was calculated using Debye-Scherre formula. FESEM technique was used to study the morphology of the sample which depicts its porous nature. High-Resolution Transmission Electron Microscopy (HRTEM) analysis provided an average particle size measurement of 65 ± 2.04nm. The phosphor's photoluminescence (PL) excitation spectrum revealed distinct peaks in the ultraviolet (UV) and near-ultraviolet (near UV) regions, aligning with the characteristics of Dy3+ ions. Four emission peaks were observed in the PL spectra at various wavelengths: 4F9/2→6H15/2 (482nm), 4F9/2→6H13/2 (578nm), 4F9/2→6H11/2 (663nm) and 4F9/2→6H9/2 (700nm). Near-white light emission was observed at the Commission International de l'Eclairage (CIE) coordinates of Dy3+ activated LiMgPO4 [LMP] phosphor, which were (x = 0.41, y = 0.42) with color purity of 49.20%. The band gap of the prepared phosphor was calculated using diffuse reflectance spectra, yielding a value of 4.47 ± 0.02eV. The results indicated that the synthesized phosphor had potential for various illumination applications when combined with other phosphors under near-UV stimulation.

Switchable planar chirality and spin texture in highly ordered ferroelectric hybrid perovskite domains

Chiral organic-inorganic hybrid perovskites offer a promising platform for developing non-linear chiro-optical applications and chiral-induced spin selectivity. Here, we show that achiral hybrid perovskites that have highly ordered ferroelectric domains with orthogonal polarization exhibit planar chirality, as manifested by second harmonic generation with strong circular dichroism. Interestingly, the handedness of the second harmonic generation circular dichroism response can be alternatingly switched between orthogonally polarized domains and domain walls. To correlate the origin of planar chirality in these domains, atom-resolved atomic force microscopy is used to reveal distinct arrangements of atomic rows in these ferroelectric crystals that indicate planar symmetry breaking. Remarkably, a large SHG anisotropy factor of 0.41 is measured at the domain wall. Additionally, spatially resolved two-photon photoluminescence excitation measurement provide evidence of larger Rashba spin-splitting in these chiral ferroelectric domains compared to domain-free areas. Our discoveries of domain-dependent planar chirality and spin texture hold great promise for advancement of domain-specific chiro-optical applications.

Impact of exciton fine structure on the energy transfer in magic-sized (CdSe)13 clusters

Magic-sized (CdSe)13 clusters (MSCs) represent a material class at the boundary between molecules and quantum dots that exhibit a pronounced and well separated excitonic fine structure. The characteristic photoluminescence is composed of exciton bandgap emission and a spectrally broad mid-gap emission related to surface defects. Here, we report on a thermally activated energy transfer from fine-structure split exciton states to surface states by using temperature dependent photoluminescence excitation spectroscopy. We demonstrate that the broad mid-gap emission can be suppressed by a targeted Mn-doping of the MSC leading to the characteristic orange luminescence of the 4T1 → 6A1 Mn2+ transition. The energy transfer to the Mn2+ states is found to be significantly different than the transfer to the surface defect states, as the activation of the dopant emission requires a spin-conserving charge carrier transfer that only dark excitons can provide.

Synthesis of white light emanating mixed lanthanide complexes with organic ligand for laser and optoelectronic applications

A series of mixing of complexes [EuxTb1-x.L3] was synthesized using the solvent-assisted grinding method. The chemical composition of complexes is determined by elemental analysis. Energy dispersive X-ray analysis (EDAX) was applied to ascertain the purity of complexes. The morphology and nature of the synthesized complex were investigated using scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). The photoluminescent excitation (PL) and photoluminescent emission (PLE) spectra were examined as a function of the concentration of Eu3+ and Tb3+ ions to predict the tuning of color in both state solution and solid. Thermogravimetric data analysis reveals that these complexes have good thermal stability, supporting their application in producing organic light-emitting diodes. The radiative rate (Arad), quantum efficiency (φ), and JO intensity parameters (Ωλ) were calculated. Studying these complexes' Urbach energy, optical band gap, and refractive index suggests their potential application in semiconductor and solar cell devices. The Commission International de I'Eclairage 1931 (CIE) coordinates (x,y) can be obtained from the emission spectra of complexes, indicating that color can be adjusted to nearly white light (x = 0.3201,y = 0.3319) by changing the Tb3+ and Eu3+ ion concentrations.

Robust single modified divacancy color centers in 4H-SiC under resonant excitation

Color centers in silicon carbide (SiC) offer exciting possibilities for quantum information processing. However, the challenge of ionization during optical manipulation leads to charge variations, hampering the efficacy of spin-photon interfaces. Recent research predicted that modified divacancy color centers can stabilize their charge states, resisting photoionization. This study presents a method for precisely creating single divacancy arrays in 4H-SiC using a focused helium ion beam. Photoluminescence tests reveal consistent emission with minimal linewidth fluctuations (∼50 MHz over 3 h). By measuring the ionization rate for different polytypes of divacancies, we found that the modified divacancies are more robust against resonant excitation. Furthermore, angle-resolved photoluminescence excitation spectra unveil two resonant-transition lines with orthogonal polarizations. Enhanced optical and spin characteristics were notably observed in these color centers compared to those generated through carbon-ion and shallow implantation methods, positioning modified divacancies as promising contenders for advancing quantum networking.

Organic Crystal with Anti‐Stokes Photoluminescent Excitation and Thermally Activated Delayed Fluorescence Features

Thermal activation process utilizes environmental thermal energy to help supplement energy for the nonspontaneous energy‐consuming upconversion physical transitions with positive free energy change (ΔG > 0). Reverse intersystem crossing (rISC) and hot band absorption are two kinds of thermal activation transitions. Thermally activated delayed fluorescence (TADF) materials with rISC have significantly propelled advancements in organic semiconductors. Hot band absorption, enables anti‐Stokes photoluminescence, offering a promising route for efficient photon upconversion. In this work, we constructed a crystal consisting of a donor‐acceptor type TADF molecule, DPQ‐DPAC, demonstrating dual thermal activation properties of hot band absorption with a notable 0.1 eV anti‐Stokes shift emission and proficient TADF performance. Only in the crystal TADF efficiency facilitates and the photoluminescence quantum yield elevates to an impressive 90.8%. Combining the extended absorption spectrum, these enhancements collectively realize anti‐Stokes photoluminescence in crystal. Experimental and theoretical results on the DPQ‐DPAC crystal indicate optimizations in its conformational and vibrational modes, resulting in enhancements to its properties. This finding provides insight into crafting organic materials with thermally activated functionalities and contributes to fully exploiting the potential of organic materials, further advancing versatile materials applications.

Organic Crystal with Anti-Stokes Photoluminescent Excitation and Thermally Activated Delayed Fluorescence Features.

Thermal activation process utilizes environmental thermal energy to help supplement energy for the nonspontaneous energy-consuming upconversion physical transitions with positive free energy change (ΔG > 0). Reverse intersystem crossing (rISC) and hot band absorption are two kinds of thermal activation transitions. Thermally activated delayed fluorescence (TADF) materials with rISC have significantly propelled advancements in organic semiconductors. Hot band absorption, enables anti-Stokes photoluminescence, offering a promising route for efficient photon upconversion. In this work, we constructed a crystal consisting of a donor-acceptor type TADF molecule, DPQ-DPAC, demonstrating dual thermal activation properties of hot band absorption with a notable 0.1 eV anti-Stokes shift emission and proficient TADF performance. Only in the crystal TADF efficiency facilitates and the photoluminescence quantum yield elevates to an impressive 90.8%. Combining the extended absorption spectrum, these enhancements collectively realize anti-Stokes photoluminescence in crystal. Experimental and theoretical results on the DPQ-DPAC crystal indicate optimizations in its conformational and vibrational modes, resulting in enhancements to its properties. This finding provides insight into crafting organic materials with thermally activated functionalities and contributes to fully exploiting the potential of organic materials, further advancing versatile materials applications.

Investigation of inter-dot tunnelling effect in hybrid coupled QDs heterostructures for short-wave infrared detection (SWIR) application

This paper explores the coupling between two different types of dots for enhancing the performance of p type/hole based (p-i-p) quantum dot infrared photodetectors (QDIPs). There are two possible con: Stranski-Krastanov (SK) QDs can be deposited on submonolayer (SML) QDs, or the SML QDs can be deposited first, followed by SK QDs. Here, both configurations are tried, and the fact that the tunnelling improves with a decrease in the barrier is exploited. The tunnelling of carriers from one QD to another QD is facilitated by the overlap of their wavefunctions, which depends on their spatial separations between the dots. A smaller barrier will lead to enhanced tunnelling probability. Utilising this idea, samples with 20 nm and 7.5 nm barriers between the QDs are grown with both types of configurations. An enhancement is anticipated in the absorption and carrier lifetime of the p-i-p QDIP structures, making them well-suited for detection in short-wavelength infra-red regions. The p-i-p configuration with the active layers of coupled QDs sandwiched between p-type dopped layers, can effectively absorb SWIR photons and generate long-lived carriers for improved photodetection performance. With the help of Photoluminescence (PL), Photoluminescence Excitation (PLE), and X-ray Diffraction (XRD) experiments, we expect large dispersion in SK on SML configuration, significantly improved carrier transfer via tunnelling and thermalisation and, changes in dot density for both of the configurations. Development of a more efficient SWIR device is expected by the insightful understanding of carrier transfer by tunnelling and thermalization with respect to the barrier thickness in the coupled QD based heterostructures.

Solidified Salt Melts of the NaCl-KCl-CeF3-EuF3 System as Promising Luminescent Materials.

This study presents the results of investigating the interaction between the CeF₃-EuF₃ system and the NaCl-KCl salt melt using spectroscopic methods. It was found that CeF₃ ions undergo no significant changes upon dissolution in the NaCl-KCl melt. In contrast, the dissolution of EuF₃, both individually and within the CeF₃-EuF₃ system, is accompanied by redox reactions leading to the formation of Eu2⁺. The diffuse reflectance spectra of both the bottom (insoluble sediment) and upper parts of the solidified salt melt in the UV range indirectly indicate photoluminescence excitation from Ce3⁺ and Eu2⁺ ions. In addition, absorption bands in the near-IR region (1900-2300 cm⁻1) confirm the retention of some Eu3⁺ ions in the salt melt. The study explored the effects of various factors-including sample composition, excitation wavelength, prior and subsequent heat treatment, and medium composition-on the excitation and emission spectra of the samples. Intense 5d-4f luminescence of Ce3⁺ and Eu2⁺ ions (at 330 and 430 nm, respectively) was observed predominantly in the upper part of the salt melts, along with much weaker 4f-4f luminescence from Eu3⁺ ions. Certain parameters were optimized to reduce the luminescence contribution from Ce3⁺ and especially Eu3⁺ ions while enhancing the luminescence of Eu2⁺ ions. Solidified salt solution-melts of the NaCl-KCl-CeF₃-EuF₃ system show promise as materials for developing solar ultraviolet radiation detectors.

Deep Ultraviolet Excitation Photoluminescence Characteristics and Correlative Investigation of Al-Rich AlGaN Films on Sapphire.

AlGaN is attractive for fabricating deep ultraviolet (DUV) optoelectronic and electronic devices of light-emitting diodes (LEDs), photodetectors, high-electron-mobility field-effect transistors (HEMTs), etc. We investigated the quality and optical properties of AlxGa1-xN films with high Al fractions (60-87%) grown on sapphire substrates, including AlN nucleation and buffer layers, by metal-organic chemical vapor deposition (MOCVD). They were initially investigated by high-resolution X-ray diffraction (HR-XRD) and Raman scattering (RS). A set of formulas was deduced to precisely determine x(Al) from HR-XRD data. Screw dislocation densities in AlGaN and AlN layers were deduced. DUV (266 nm) excitation RS clearly exhibits AlGaN Raman features far superior to visible RS. The simulation on the AlGaN longitudinal optical (LO) phonon modes determined the carrier concentrations in the AlGaN layers. The spatial correlation model (SCM) analyses on E2(high) modes examined the AlGaN and AlN layer properties. These high-x(Al) AlxGa1-xN films possess large energy gaps Eg in the range of 5.0-5.6 eV and are excited by a DUV 213 nm (5.8 eV) laser for room temperature (RT) photoluminescence (PL) and temperature-dependent photoluminescence (TDPL) studies. The obtained RTPL bands were deconvoluted with two Gaussian bands, indicating cross-bandgap emission, phonon replicas, and variation with x(Al). TDPL spectra at 20-300 K of Al0.87Ga0.13N exhibit the T-dependences of the band-edge luminescence near 5.6 eV and the phonon replicas. According to the Arrhenius fitting diagram of the TDPL spectra, the activation energy (19.6 meV) associated with the luminescence process is acquired. In addition, the combined PL and time-resolved photoluminescence (TRPL) spectroscopic system with DUV 213 nm pulse excitation was applied to measure a typical AlGaN multiple-quantum well (MQW). The RT TRPL decay spectra were obtained at four wavelengths and fitted by two exponentials with fast and slow decay times of ~0.2 ns and 1-2 ns, respectively. Comprehensive studies on these Al-rich AlGaN epi-films and a typical AlGaN MQW are achieved with unique and significant results, which are useful to researchers in the field.

A novel red-emitting InScW3O12:Eu3+ phosphor with anti-thermal-quenching performance for high-power WLED applications

A series of red-emitting InScW3O12:Eu3+ (ISWO:Eu3+) phosphors with anti-thermal-quenching performance were successfully synthesized by conventional solid-state reaction. The phase structure and luminescent properties of ISWO:Eu3+ were systematically studied. The photoluminescence excitation (PLE) spectrum showed that ISWO:Eu3+ phosphor can be effectively matched with commercial ultraviolet (UV), violet and blue light chips. The main emission peak of the phosphor was located at 613 nm, which was attributed to the electric dipole transition 5D0 → 7F2. Under the optimal excitation, the prepared ISWO:0.08Eu3+ phosphor showed excellent anti-thermal-quenching performance, its photoluminescence (PL) intensity at 180 °C reached 157.4 % of initial intensity at room temperature. At 465 nm excitation, it also exhibited the anti-thermal-quenching property and the PL intensity remained 115.1 % at 150 °C of that at room temperature. In situ XRD analysis revealed that the lattice contraction resulting in an increase in structural rigidity as the temperature rising, which caused the change of Eu3+ local environment and improved the PL intensity. Finally, a series of warm white LED devices under varying power density conditions with stable output were prepared using the red ISWO:0.08Eu3+ phosphor, indicating that the ISWO:Eu3+ phosphor with excellent anti-thermal-quenching performance has potential application prospects in high-power white light-emitting diodes (WLEDs).

The Role of Ce3+ Co-doping in the Luminescent Enhancement of Bi3+ Emission and Bi3+→Bi2+ Conversion in LiLaP4O12 Host

This work investigates the luminescent versatility of the LiLa(1-x-y)BixCeyP4O12 system as a scintillator material capable of displaying emission in a range from the blue to the red region depending on the Ce3+ concentration. The LiLaP4O12 host has been proven to be useful as a scintillator material when doped with some rare earths and with bismuth ions. However, the process of bismuth valence change induced by X-rays, when inserted in the LiLaP4O12 matrix, is not known to date, as well as whether this can be controlled and used to enhance the luminescence emission. To determine the mechanism of interaction between the Ce3+ and Bi3+ ions in the LiLaP4O12 host, doped and co-doped samples were synthesized and investigated. Identification of crystalline phase was carried out with X-Ray Powder Diffraction. The luminescent properties were studied via photoluminescence emission and excitation using synchrotron radiation. Scintillator features were studied through radioluminescence emission spectrum. The results indicate that Ce3+ transfers either energy or electrons to Bi3+ when excited with UV (5.2 eV) or X-rays, respectively. In the first case, the overall white luminescence is improved, while in the latter, enhanced red luminescence from Bi2+ was observed, indicating the valence change of Bi ions, assisted by Ce co-dopant. A luminescent mechanism, based on the vacuum-referred binding energy model applied to the experimental data, was proposed to explain the Bi2+ emission, deepening the understanding of the Bi emission mechanism and opening the possibility of tailoring the Bi2+/Bi3+ proportion varying the Ce-co-doping concentration.

Study of the microstructure and temperature dependent luminescence of Na- and Li-beta gallia rutile compounds

We present the structural, vibrational and luminescence properties of Na- and Li- stabilized gallium-titanium oxides studied by optical spectroscopy techniques. The microstructure and characteristic vibrational modes of this homologous series, which are not well known, have been determined with the aid of Raman spectroscopy and compared to density functional theory (DFT) calculations. On the other hand, intense cathodoluminescence bands in the visible and in the near-infrared are observed depending on the term of the series and related to native defects. Besides, the study of the temperature evolution of the photoluminescence and photoluminescence excitation spectra has allowed us to determine both the band gap energy temperature dependence as well as to get some insight into the luminescence mechanisms of the defect-related emissions in these compounds. The results pave the way to exploit the physical properties of these Na- and Li- gallium titanate series in functional optoelectronic devices to operate from the ultraviolet to the infrared range.

Photoswitchable AIE‐Active Supramolecular Self‐Assemblies for Biosensing and Bioimaging

AbstractPhotoswitchable fluorescent self‐assemblies exhibiting aggregation‐induced emission (AIE) properties have garnered widespread attention. Due to their great adaptiveness and responsiveness towards different wavelengths required by photoreaction, photo‐isomerization, and photoluminescence excitation, these fluorescent self‐assemblies show diverse emission behavior in a spatial, temporal, and polychromatic manner. Integrating organic photoswitches and AIE fluorophores, these photoluminescent nano‐assemblies have been proven to be an effective approach, allowing the development of sophisticated systems for drug release and cell regulation that can be precisely manipulated through light or other stimuli. This review systematically encapsulates recent advances in photoswitchable fluorescent self‐assemblies under multi‐scenario biological applications. The construction of photoswitchable AIE fluorophores through covalent and non‐covalent interactions and their multimodal regulation are detailed, along with their biological applications in biosensing, bioimaging, and drug therapy.