Near-infrared Laser Excitation Research Articles

Enhancement mechanism of red up-conversion emission in single NaYbF<sub>4</sub>:2%Er<sup>3+</sup>@NaYbF<sub>4 </sub>micron core-shell structure

The construction of core-shell structure can effectively reduce the quenching effect on the surface of material and regulate ion-ion interaction, which has become one of the effective ways to enhance and regulate the spectral characteristics of rare-earth upconversion luminescent materials. In this paper, a variety of NaYbF<sub>4</sub>: 2%Er<sup>3+</sup> micron core-shell structures are constructed with the help of epitaxial growth technology, effectively improving the red up-conversion emission of Er<sup>3+</sup> ions. The prepared microcrystals with core-shell structures are of hexagonal phase microdisks, and their sizes are relatively uniform. In order to better obtain the material spectral data, a confocal microscopic spectroscopy is used to study spectral properties. Under 980 nm near-infrared laser excitation, the red emission intensity of single NaYbF<sub>4</sub>:2%Er<sup>3+</sup>@NaYbF<sub>4</sub>@NaYF<sub>4</sub> core-shell-shell microdisk is 4.6 times higher than that of NaYbF<sub>4</sub>:2%Er<sup>3+</sup> micron disk, and the red-to-green ratio increases from 6.3 to 8.1. Meanwhile, Ho<sup>3+</sup> ions are introduced into the NaYbF<sub>4</sub>:2%Er<sup>3+</sup>@NaYbF<sub>4</sub>: 2%Ho<sup>3+</sup> @NaYF<sub>4</sub> core-shell-shell microdisk, and the red emission intensity is nearly 6.7 times higher than that of single NaYbF<sub>4</sub>: 2%Er<sup>3+</sup> microdisk, and the red-to-green ratio increases from 6.3 to 9.4 through the interaction between ions. The microcrystal spectral characteristics and luminescence kinetics of different core-shell structures are studied, showing that the red emission enhancement of Er<sup>3+</sup> ions is mainly derived from the construction of different core-shell structures, which can effectively enhance the cross-relaxation between Er<sup>3+</sup> ions, the energy back transfer between Yb<sup>3+</sup> and Er<sup>3+</sup> ions, and the energy transfer from Ho<sup>3+</sup> ions to Er<sup>3+</sup> ions. The micron core-shell structures with efficient red emission in this study has great application prospects in the fields of luminescence, anti-counterfeiting and optoelectronic devices.

Detection and identification of leukemic and normal cells using Raman spectroscopy and multivariate statistical analysis

Raman spectroscopy technique was successfully employed to study the difference between leukemic cells (Jurkat cell line) and normal human bone marrow mononuclear cells using near-infrared laser (785 nm) excitation in this study. Significant differences in Raman spectra from two kinds of cell lines showed special changes in the percentage of biochemical constituents in different cells. The obtained spectral data were used to develop diagnostic algorithms by multivariate statistical analysis, including principal component analysis combined with linear discriminate analysis. The multivariate statistical analysis method for classification between cancer and normal cells has achieved good differentiation with high diagnostic sensitivity (100%), specificity (100%), and accuracy (100%), respectively. These results showed that Raman spectroscopy is a novel, nondestructive method, that provided interesting information about the changes in biochemical properties of cells. Raman spectroscopy combined with multivariate statistical analysis can serve as a potential clinical diagnosis method of leukemia.

Molecular Vibrations in Chiral Europium Complexes Revealed by Near-Infrared Raman Optical Activity.

Raman optical activity (ROA) is commonly measured with green light (532nm) excitation. At this wavelength, however, Raman scattering of europium complexes is masked by circularly polarized luminescence (CPL). This can be avoided using near-infrared (near-IR, 785nm) laser excitation, as demonstrated here by Raman and ROA spectra of three chiral europium complexes derived from camphor. Since luminescence is strongly suppressed, many vibrational bands can be detected. They carry a wealth of structural information about the ligand and the metal core, and can be interpreted based on density functional theory (DFT) simulations of the spectra. For example, jointly with ROA experimental data, the simulations make it possible to determine absolute configuration of chiral lanthanide compounds in solution.

Dual-mode photoluminescent microspheres with silica core, separator layer and envelope for anti-counterfeiting ink

The microsphere is concentrically constructed on the basis of SiO2 nanocore on which Gd2O3:Yb,Er upconversion luminescent layer, SiO2 separator, Gd2O3:Ln@SiO2 (Ln3+ = Tb3+, Eu3+) downconversion luminescent layer, and SiO2 envelope are successively deposited by means of wet chemistry method. Under 980 nm near-infrared laser excitation, the microspheres emit bright upconverted green light due to Gd2O3:Yb,Er luminescent layer. While, under 254 nm portable ultraviolet lamp irradiation, they produce red and green downconversion fluorescence because of Gd2O3:Ln (Ln3+ = Tb3+ or Eu3+) luminescent layer. The silica core fixes the luminescence center, reduces non radiative transitions caused by molecular vibration, enhances fluorescence intensity, and saves rare earth resources. Impressively, the silica separator layer isolates the upconversion luminescence of Er3+ and downconversion of Eu3+, preventing cross relaxation and quenching of Er3+ fluorescence. The silica envelope plays a crucial role in the photoluminescence of the prepared microspheres. The photoluminescence quantum yield of the microspheres initially increases from 90.4 % to 95.9 % and then decreases to 82.9 % as the thickness of SiO2 layer on the ∼3 nm-thick Gd2O3:Ln shell rises from 3 nm to 16 nm. The absorption of photons reaches its maximum when the SiO2 layer is 8 nm thick. This thickness corresponds to the lowest rate constant for non-radiative transitions. The proto inks prepared from the dual-mode microspheres exhibit good performance including good luminescence and high dispersibility for practical anti-counterfeiting applications.

Direct Investigation of Excited C60 Dianion and Its Intramolecular Electron Transfer Behaviors.

For the first time, the dynamics of excited fullerene dianions and associated intramolecular electron transfer (ET) were directly investigated by using femtosecond pump-probe laser flash photolysis on selectively reduced C60, pyrrolidino[60]fullerene (C60H), and dyads including C60-naphthalenediimide (NDI) and C60-pyromellitimide (PI). Upon near-infrared laser excitation, the excited dianion of C60 or C60H displayed two states with lifetimes of less than one and several tens of ps, attributed to prompt internal conversion from the theoretically predicted Sn state. Furthermore, the ET processes from the excited C602- in dyad molecules, including C602--NDI•- and C602--PI•-, were confirmed with varied ET rate constants due to the difference in the driving force for ET. The current findings provide a clear description of the hitherto uncharted excited-state and photoinduced ET characteristics of fullerene dianions, paving the way for photochemical studies of excited multi-ions (excited multi-polarons) and their application in organic semiconducting materials.

Self-Assembled Aza-BODIPY and Iron(III) Nanoparticles for Photothermal-Enhanced Chemodynamic Therapy in the NIR-II Window.

Despite its promising potential in cancer treatment, synergistic photothermal/chemodynamic therapy remains underdeveloped with regard to the utilization of metal-organic materials under second near-infrared (NIR-II) laser excitation. Herein, we report a three-dimensional network constructed via the metal coordination between catechol-functionalized aza-boron dipyrromethenes and iron ions (ABFe), which was further encapsulated by F127 to obtain ABFe nanoparticles (NPs) for combined photothermal/chemodynamic therapy. ABFe NPs exhibited intense absorption in the NIR-II range and negligible fluorescence. Upon 1064 nm laser irradiation, ABFe NPs showed high photothermal conversion efficiency (PCE = 55.0%) and excellent photothermal stability. The results of electron spin resonance spectra and o-phenylenediamine chromaticity spectrophotometry proved that ABFe NPs were capable of generating harmful reactive oxygen species from hydrogen peroxide for chemodynamic therapy, which was promoted by photothermal performance. Notably, in vitro and in vivo experiments demonstrated the great potential of ABFe NPs in photoacoustic imaging and photothermal-enhanced chemodynamic therapy under NIR-II laser irradiation. Therefore, the current work presents a prospective NIR-II excitation therapeutic nanomedicine for combination therapy, offering a novel strategy for simultaneously achieving extended NIR absorption of aza-BODIPY and enhanced chemodynamic therapy with metal-organic materials.

Investigation of calcium-silicate content and conversion degree of resin-based pulp capping materials

The present study aimed to measure the microstructure of the TheraCal LC (Bisco Inc., Schaumburg, IL) and Calciplus LC (Imicryl, Konya, Turkey) and to investigate the effect of excitation durations and different light sources on their ‘degree of conversion’ properties. Three excitation modes of the resinous pulp capping materials were tested at 5, 10, and 20-s: light-emitting diode, and near-infrared laser excitation at 532 and 785 nm wavelengths. Resinous materials and excitation durations factors were analyzed with the two-way ANOVA test and Tukey Post Hoc tests (α = 0.05). It is found that the near-infrared laser cannot polymerize the samples and TheraCal LC had greater mean values than Calciplus LC at 5, 10, and 20-s (p < 0.001, p = 0.011, and p = 0.062, respectively). Energy-dispersive X-ray spectroscopy and X-ray powder diffraction analysis were used to assess the calcium-silicate content. Calcium-silicate phases were observed in TheraCal LC but these phases did not exist in the Calciplus LC. TheraCal LC and Calciplus LC have similarities in their conversion degree properties with LED excitations at 20-s, however, the calcium-silicate content measured in the experiments is not in agreement with the data of the Calciplus LC declared by the manufacturer.

Hot Carrier-Induced Nonlinear Photoluminescence in a Thin Indium Tin Oxide Layer Patterned by Ga Ion Beam Milling

This paper explores the nonlinear photoluminescence emitted by indium tin oxide (ITO) thin layers patterned by focused gallium ion beam milling. Using tightly focused near-infrared femtosecond pulsed laser excitation, a broad up-converted luminescence spectrum spanning the visible is detected. The intensity of the luminescence follows a nonmonotonous relationship with milling doses and can be related to the modification of the ITO electronic band structure by the implantation of Ga ions. The shape and the power dependence of the spectrum share strong similarities with those of nonlinear photoluminescence arising from metals. The results are consistent with a nonlinear process originating from the radiative decay of photogenerated hot carriers. The thermal coefficient relating the carrier temperature to the laser intensity is determined as a function of milling dose.

Construction of NaYF4: Yb, Ho/B, N-GQDs nanocomposites for double anti-counterfeiting fluorescence ink

Fluorescent nanomaterials with multiple anti-counterfeiting play a vital role in economic and social fields in our daily lives. In this work, a hybridized composite of boron and nitrogen co-doped graphene quantum dots (B, N-GQDs) and lanthanide-doped up-conversion NaYF4 was prepare for a double anti-counterfeiting application. The composite was obtained by one-pot hydrothermal method and it was commixed with glycerol in a ratio of 4 : 1 to prepare a fluorescence ink, which exhibited independent blue and green fluorescence emissions under ultraviolet light and near-infrared laser excitation. Therefore, it had a considerable application in confidential communications, logo designing and file encryptions.

Upconversion‐Enabled In Situ Growth of Silver Nanostructures Mediated by Cavity Resonance in Single Microrod (Adv. Mater. Interfaces 15/2022)

Upconversion-Enabled Growth of Silver Nanostructures In article number 2200029, Huilin He, Yan Jun Liu, and co-workers demonstrate that the upconversion emission from the hexagonal NaYF4 microrods under the near-infrared laser excitation enables the photochemical reaction to grow the Ag nanoparticles (AgNPs). Additionally, AgNPs aggregate along the leaked sites of cavity-induced resonances inside the microrod, forming a grating-like Ag nanostructure.

Upconversion‐Enabled In Situ Growth of Silver Nanostructures Mediated by Cavity Resonance in Single Microrod

Solution-based photochemical reaction is widely utilized in the syntheses of metallic nanocrystals. Although seedless photochemical reaction can avoid pre-treatments, it relies on long, high-energy radiation. Here, this work demonstrates an upconversion-enabled seedless photochemical approach to synthesize grating-like silver nanostructures on a hexagonal NaYF4 microrod via a near-infrared laser excitation. Experimental results show that upconversion emission enables the nucleation and growth of Ag nanoparticles. Meanwhile, the emission can be also precisely tuned and enhanced by in situ growth of silver nanoparticles on the NaYF4 and NaYF4@SiO2 microrods. The maximum enhancement factor of 2 in overall emissions is achieved for the NaYF4@SiO2 microrod. This fabrication approach and results visually confirm the cavity resonance of excitation light inside the microrod via the distribution of Ag nanostructures. Moreover, the in situ grown Ag nanostructures provide a tunable far-field upconversion emission via the plasmonic effect, which is potentially useful for tunable microlasers, biosensing, antibacterial, and catalytic applications.

Indocyanine-type Infrared-820 Encapsulated Polymeric Nanoparticle-Assisted Photothermal Therapy of Cancer.

Organic small-molecule photosensitizers are well-characterized and known for the light-responsive treatment modality including photodynamic therapy. Compared with ultraviolet–visible (UV–vis) light used in conventional photodynamic therapy with organic photosensitizers, near-infrared (NIR) light from 700 to 900 nm is less absorbed and scattered by biological tissue such as hemoglobin, lipids, and water, and thus, the use of NIR excitation can greatly increase the penetration depth and emission. Additionally, NIR light has lower energy than UV–vis that can be beneficial due to less activation of fluorophores present in tissues upon NIR irradiation. However, the low water stability, nonspecific distribution, and short circulation half-life of the organic photosensitizers limit its broad biological application. NIR responsive small-molecule fluorescent agents are the focus of extensive research for combined molecular imaging and hyperthermia. Recently a new class of NIR dye, IR-820 with excitation and emission wavelengths of 710 and 820 nm, has been developed and explored as an alternative platform to overcome some of the limitations of the most commonly used gold nanoparticles for photothermal therapy of cancer. Herein, we synthesized a core–shell biocompatible nanocarrier envelope made up of a phospholipid conjugated with poly(ethylene glycol) as a shell, while poly(lactic glycolic acid) (PLGA) was used as a core to encapsulate IR-820 dye. The IR-820-loaded nanoparticles were prepared by nanoprecipitation and characterized for their physicochemical properties and photothermal efficiency. These nanoparticles were monodispersed and highly stable in physiological pH with the hydrodynamic size of 103 ± 8 nm and polydispersity index of 0.163 ± 0.031. The IR-820-loaded nanocarrier showed excellent biocompatibility in the dark, whereas remarkable phototoxicity was observed with breast cancer cells (MCF-7) upon NIR laser excitation. Therefore, the IR-820-loaded phospholipid mimicking biodegradable lipid-polymer composite nanoparticles could have great potential for cancer theranostics.

Facile synthesis of near-infrared responsive on-demand oxygen releasing nanoplatform for precise MRI-guided theranostics of hypoxia-induced tumor chemoresistance and metastasis in triple negative breast cancer

BackgroundHypoxia is an important factor that contributes to chemoresistance and metastasis in triple negative breast cancer (TNBC), and alleviating hypoxia microenvironment can enhance the anti-tumor efficacy and also inhibit tumor invasion.MethodsA near-infrared (NIR) responsive on-demand oxygen releasing nanoplatform (O2-PPSiI) was successfully synthesized by a two-stage self-assembly process to overcome the hypoxia-induced tumor chemoresistance and metastasis. We embedded drug-loaded poly (lactic-co-glycolic acid) cores into an ultrathin silica shell attached with paramagnetic Gd-DTPA to develop a Magnetic Resonance Imaging (MRI)-guided NIR-responsive on-demand drug releasing nanosystem, where indocyanine green was used as a photothermal converter to trigger the oxygen and drug release under NIR irradiation.ResultsThe near-infrared responsive on-demand oxygen releasing nanoplatform O2-PPSiI was chemically synthesized in this study by a two-stage self-assembly process, which could deliver oxygen and release it under NIR irradiation to relieve hypoxia, improving the therapeutic effect of chemotherapy and suppressed tumor metastasis. This smart design achieves the following advantages: (i) the O2 in this nanosystem can be precisely released by an NIR-responsive silica shell rupture; (ii) the dynamic biodistribution process of O2-PPSiI was monitored in real-time and quantitatively analyzed via sensitive MR imaging of the tumor; (iii) O2-PPSiI could alleviate tumor hypoxia by releasing O2 within the tumor upon NIR laser excitation; (iv) The migration and invasion abilities of the TNBC tumor were weakened by inhibiting the process of EMT as a result of the synergistic therapy of NIR-triggered O2-PPSiI.ConclusionsOur work proposes a smart tactic guided by MRI and presents a valid approach for the reasonable design of NIR-responsive on-demand drug-releasing nanomedicine systems for precise theranostics in TNBC.Graphical

Improved ionization and dissociation energies of the deuterium molecule

The ionization energy of D$_2$ has been determined experimentally from measurements involving two-photon Doppler-free vacuum-ultraviolet pulsed laser excitation and near-infrared continuous-wave laser excitation to yield $E_\mathrm{I}(\mathrm{D}_2)=124\,745.393\,739(26)$ \wn. From this value, the dissociation energy of D$_2$ is deduced to be $D_0$(D$_2$) = 36\,748.362\,282(26) \wn, representing a 25-fold improvement over previous values, and found in good agreement (at $1.6\sigma$) with recent ab initio calculations of the 4-particle nonadiabatic relativistic energy and of quantum-electrodynamic corrections up to order $m\alpha^6$. This result constitutes a test of quantum electrodynamics in the molecular domain, while a perspective is opened to determine nuclear charge radii from molecules.

Tumor-targeted biocatalyst with self-accelerated cascade reactions for enhanced synergistic starvation and photodynamic therapy

Combination therapy has been considered as an attractive strategy in complementary anticancer treatment. However, its therapeutic outcomes could be inhibited by the tumor microenvironment (TME) such as hypoxia and insufficient endogenous hydrogen peroxide concentration. Herein, we typically design a multilayered porous biocatalyst (USCGP) realizing cascade reactions-enhanced synergistic cancer therapy. Glucose oxidase (GOD) loaded on USCGP catalyzes glucose decomposition accompanied by regulating TME, which activates double enzyme-like catalysis of USCGP. Concurrently, the cascade reactions between GOD and cerium oxide (CeO2) not only promote nutrition consumption but also enhance the generation of hydroxyl radicals (•OH). In addition, under near-infrared (NIR) laser excitation, upconversion nanoparticles (UCNPs) in the core could convert NIR light to UV emission to trigger photocatalysis reactions of CeO2, achieving efficient spatio-temporal controllable photodynamic therapy. In particular, the modification of poly(ethylene glycol)-cyclo (Arg-Gly-Asp-d-Phe-Lys) (NH2-PEG1000-cRGDfK, abbreviated as PEG-cRGDfK) facilitates the accumulation of USCGP into tumor cells. Furthermore, USCGP could also be served as excellent contrast agent for computed tomography (CT) imaging in tumor diagnosis. Taken together, USCGP exhibits high-performance in tumor suppression with minimal side effects in vitro and in vivo, realizing additive cooperation of long-term starvation and robust photodynamic treatment strategy.

Surface-Enhanced Raman Scattering Bioimaging with an Ultrahigh Signal-to-Background Ratio under Ambient Light.

Surface-enhanced Raman scattering (SERS) nanoprobes have attracted particular interests in the field of bioimaging owing to their high sensitivity and specificity of the fingerprint spectrum. However, the limited signal-to-background ratio (SBR) in SERS imaging and the requirement to perform imaging in a dark environment have largely hindered its biomedical application. To circumvent this, we have developed a type of bio-orthogonal nanoprobes for SERS imaging with an ultrahigh SBR and ambient light anti-interference ability. The core-shell nanoprobes exhibit strongly enhanced Raman signals and depress the background from photoluminescence of metallic nanoparticles by off-resonance excitation and from the Raman scattering and auto-fluorescence of tissues by near-infrared laser excitation. Such nanoprobes have achieved an SBR of over 100 in SERS bioimaging, 5 times higher than the traditional on-resonant nanoprobes, and their bio-orthogonal signal in the Raman-silent region renders the anti-interference capability under ambient light. The development of these SERS probes opens up a new era for the future applications of Raman imaging in clinical medicine.

Bi-functional nanocomposite based on phosphor and carbon nanotubes for tumor ablation in a photothermal fiber system with temperature feedback

Photothermal therapy has aroused tremendous attention in the biomedical field as a promising and less-invasive method for tumor ablation, but its development is greatly limited due to lack of efficient and controllable photothermal materials in treatment. Here, a dual-functional composite based on lanthanide-doped nanoparticles and carbon nanotubes has been successfully synthesized for designing the photothermal system. Under near-infrared laser excitation, the composite could effectively convert light energy into thermal energy due to non-radiation relaxation of nanoparticles and carbon nanotubes. More importantly, the optical thermometer was constructed through the luminescence intensity ratio of different upconversion emission bands corresponding to the lanthanide ions in the nanophosphors. Furthermore, we established an optical fiber system with the developed composite for precise tumor treatment. This work verified the feasibility of accurate temperature monitoring and efficient optical heating under near-infrared laser excitation, proposed a design of multifunctional photothermal materials for tumor treatment with the unique advantages of high accuracy and low invasive burden.

Upconversion luminescence characteristics of Ho&lt;sup&gt;3+&lt;/sup&gt; ion doped single-particle fluoride micron core-chell structure

Constructing core-shell structures can effectively reduce the surface quenching effect of luminescent materials, which becomes an effective method to enhance upconversion luminescence. In this work, a series of NaLnF&lt;sub&gt;4&lt;/sub&gt;@NaLnF&lt;sub&gt;4&lt;/sub&gt; (Ln = Y&lt;sup&gt;3+&lt;/sup&gt;, Yb&lt;sup&gt;3+&lt;/sup&gt;, Ho&lt;sup&gt;3+&lt;/sup&gt;) core-shell microcrystals is successfully synthesized based on epitaxial growth technology, thereby enhancing and regulating the upconversion emission of Ho&lt;sup&gt;3+&lt;/sup&gt; ions. The results of the XRD and SEM indicate that the NaLnF&lt;sub&gt;4&lt;/sub&gt;@NaLnF&lt;sub&gt;4&lt;/sub&gt; core-shell microcrystal possesses a pure hexagonal-phase crystal structure with a rod-like shape. Meanwhile, it is found that the epitaxial growth direction of the micro-shell is not affected by the crystal characteristics in the core, but determined by the crystal characteristics of the shell. Under 980 nm near-infrared laser excitation, the upconversion luminescence properties of single microrods with different core-shell structures are investigated via a confocal microscope spectroscopy. It is found that in the NaLnF&lt;sub&gt;4&lt;/sub&gt; micro-crystal, the coated NaYF&lt;sub&gt;4&lt;/sub&gt; inert shell can also effectively reduce the quenching effect on the surface of the micro-crystal for enhancing upconversion emission. When the Yb&lt;sup&gt;3+&lt;/sup&gt; ions are introduced into NaYF&lt;sub&gt;4&lt;/sub&gt; or NaYbF&lt;sub&gt;4&lt;/sub&gt; active shell that is coated, the Yb&lt;sup&gt;3+&lt;/sup&gt; ions in the shell can effectively transfer excitation energy to Yb&lt;sup&gt;3+&lt;/sup&gt; in the core through energy migration, and then establish new energy transfer channels, thereby realizing the Ho&lt;sup&gt;3+&lt;/sup&gt; ion luminescence enhancement. For NaHoF&lt;sub&gt;4&lt;/sub&gt;@NaYbF&lt;sub&gt;4&lt;/sub&gt; core-shell microrods, the Yb&lt;sup&gt;3+&lt;/sup&gt; in the shell can transfer more excitation energy to Ho&lt;sup&gt;3+&lt;/sup&gt; ions at the adjacent interface for enhancing the overall luminescence intensity, and its higher red-green ratio is mainly due to the cross-relaxation process occurring between the Ho&lt;sup&gt;3+&lt;/sup&gt; ions at high doping concentration of Ho&lt;sup&gt;3+&lt;/sup&gt; in the NaHoF&lt;sub&gt;4&lt;/sub&gt; core. Meanwhile, the luminescence process of the micron core-shell system is further confirmed based on the luminescence characteristics of different structures and the dynamic luminescence process. It can be seen that constructing different micron core-shell structures and introducing sensitizing ions, can not only effectively enhance the luminous intensity of the micron materials, but also adjust the output color. Therefore, this research is an important experimental reference for enhancing the luminous intensity of the micron system and the precise adjustment of luminescence, and can effectively expand the applications of micron crystals in the fields of displays, micron lasers and anti-counterfeiting.

Unusual luminescence and its decay behavior of CH3NH3PbBr3 single crystals at orthorhombic phase

We investigate the luminescent property of CH3NH3PbBr3 (MAPbBr3) single crystals (SCs) by use of temperature and power dependent photoluminescence (PL) spectroscopy. An unusual PL due to trapped state emission at 580∼650 nm can be only observed at orthorhombic phase below 145 K, which is originated from the change of structural order and disorder at low temperature. At the temperature point from orthorhombic to tetragonal phase, the structural change leads to the disappearance of trapped state emission. From Raman spectra and theoretical analysis, MAPbBr3 crystal structure is susceptible to temperature, trapped state emission can be formed after photoinduced excitation due to the tilting and twisting of MA organic group, which even exist under near-infrared (NIR) femtosecond laser excitation due to two-photon absorption. Time-resolved PL (TRPL) reveals that temperature-dependent characteristics of this unusual PL coexist with intrinsic exciton recombination at orthorhombic phase. Our findings imply that it is essential to understand the photophysical property caused by the structural change of hybrid perovskite crystal.

Time-gated Raman spectroscopy for biomedical application under ambient or strong background light conditions

Many biomedical applications require measurements of Raman spectra of tissue under ambient lighting conditions. However, the background light often swamps the weaker Raman signal. The use of time-gated (TG) Raman spectroscopy based on a single photon avalanche diode (SPAD) operating in time-correlated single photon counting and near-infrared laser excitation was investigated for acquisition of Raman spectra and spectral images of biological tissue. The results obtained using animal tissue samples (adipose tissue and muscle) show that the time gating modality enables measurement of Raman spectra under background light conditions of similar quality as conventional continuous wave Raman spectroscopy in the absence of background light. Optimal suppression of the background light was observed for time gate widths of 300–1000 ps. The results also showed that TG Raman spectroscopy was able to detect subtle spectral differences required for medical diagnostics, such as differences in Raman spectra of cancer and normal tissue. While the current instrument required scanning of the grating in order to obtain full Raman spectra, leading to impractical times for multi-wavenumber Raman mapping, imaging time could be drastically reduced by spectral multiplexing (compressed detection) using digital micromirror devices or by using SPAD arrays.