Electro-optical interfacial effects on a graphene/π-conjugated organic semiconductor hybrid system

• Karolline A. S. Araujo,
• Luiz A. Cury,
• Matheus J. S. Matos,
• Thales F. D. Fernandes,
• Luiz G. Cançado and
• Bernardo R. A. Neves

Beilstein J. Nanotechnol. 2018, 9, 963–974, doi:10.3762/bjnano.9.90

• probe microscopy, optical spectroscopy (photoluminescence and Raman) and ab initio calculations. The graphene/RA interaction induces the formation of a well-organized π-conjugated self-assembled monolayer (SAM) at the interface. Such structural organization leads to the high optical emission efficiency

• influences: graphene-promoted high photoluminescence efficiency of RA and RA-induced doping and charge modulation of graphene. The results suggest that low-dimensional hybrid systems, with reciprocal modifications of the constituents’ original properties, may tailor the desired properties in future device

• properties of this novel RA SAM structure. Therefore, photoluminescence (PL) studies of RA monolayers and multilayers atop graphite microplates were performed as a function of temperature (Figure 3). Initially, in order to emulate thick and disordered RA films, a graphite microplate substrate was spread

Facile synthesis of a ZnO–BiOI p–n nano-heterojunction with excellent visible-light photocatalytic activity

• Mengyuan Zhang,
• Jiaqian Qin,
• Pengfei Yu,
• Bing Zhang,
• Mingzhen Ma,
• Xinyu Zhang and
• Riping Liu

Beilstein J. Nanotechnol. 2018, 9, 789–800, doi:10.3762/bjnano.9.72

• carrier separation efficiency, photoluminescence (PL) emission spectra was carried out and the results are displayed in Figure S4, Supporting Information File 1. Generally speaking, stronger PL intensity indicates a higher photoinduced hole–electron recombination rate, which is not in the photocatalysts

Valley-selective directional emission from a transition-metal dichalcogenide monolayer mediated by a plasmonic nanoantenna

• Haitao Chen,
• Mingkai Liu,
• Lei Xu and
• Dragomir N. Neshev

Beilstein J. Nanotechnol. 2018, 9, 780–788, doi:10.3762/bjnano.9.71

• [6][7][8][9][10]. In particular, monolayer TMDCs with direct bandgap at the K and K′ points [11] make it possible to control the valley degree freedom entirely optically. Optical pumping of excitons of a specific valley polarization has been demonstrated by polarization-resolved photoluminescence (PL

Surface-plasmon-enhanced ultraviolet emission of Au-decorated ZnO structures for gas sensing and photocatalytic devices

• T. Anh Thu Do,
• Truong Giang Ho,
• Thu Hoai Bui,
• Quang Ngan Pham,
• Hong Thai Giang,
• Thi Thu Do,
• Duc Van Nguyen and
• Dai Lam Tran

Beilstein J. Nanotechnol. 2018, 9, 771–779, doi:10.3762/bjnano.9.70

• simple chemical bath deposition and photoreduction methods. The analysis of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images, energy-dispersive X-ray spectroscopy (EDS), UV–vis absorption, and photoluminescence (PL) spectra results were used to verify the incorporation

• of plasmonic Au nanoparticles (NPs) on the ZnO film. Time-resolved photoluminescence (TRPL) spectra indicated that a surface plasmonic effect exists with a fast rate of charge transfer from Au nanoparticles to the sub-micrometer ZnO sphere, which suggested the strong possibility of the use of the

• revealed that ZnO sub-micrometer spheres were deposited on the glass substrates and Au-decorated ZnO nanostructures were confirmed. Using photoluminescence (PL) spectra and time-resolved photoluminescence (TRPL) measurements, we investigate the SPR characteristics and ZnO exciton peaks, which complement

Perovskite-structured CaTiO₃ coupled with g-C₃N₄ as a heterojunction photocatalyst for organic pollutant degradation

• Ashish Kumar,
• Christian Schuerings,
• Suneel Kumar,
• Ajay Kumar and
• Venkata Krishnan

Beilstein J. Nanotechnol. 2018, 9, 671–685, doi:10.3762/bjnano.9.62

• disk was measured by diffuse reflectance spectroscopy (DRS). DRS studies were performed on a Perkin Elmer UV–visible–NIR Lambda 750 spectrophotometer by utilizing polytetrafluoroethylene (PTFE) polymer as a diffuse reflectance standard in the wavelength range 200–800 nm. Photoluminescence (PL

• the UV and visible light regions. In addition, photoluminescence (PL) spectroscopy studies were carried out in order to study the separation and migration of photogenerated charge carriers in the CTCN heterojunction. It is well-reported in literature that recombination of electrons and holes give rise

• heterojunction. Photoluminescence spectra of g-C3N4, CT and CTCN heterojunction. Nitrogen adsorption–desorption curves for (a) g-C3N4 (b) CT and (c) CTCN heterojunction; BET surface area plots for (d) g-C3N4 (e) CT and (f) CTCN heterojunction. Time-dependent absorption spectra of RhB degradation with the CTCN

Green synthesis of fluorescent carbon dots from spices for in vitro imaging and tumour cell growth inhibition

• Nagamalai Vasimalai,
• Vânia Vilas-Boas,
• Juan Gallo,
• María de Fátima Cerqueira,
• Mario Menéndez-Miranda,
• José Manuel Costa-Fernández,
• Lorena Diéguez,
• Begoña Espiña and
• María Teresa Fernández-Argüelles

Beilstein J. Nanotechnol. 2018, 9, 530–544, doi:10.3762/bjnano.9.51

• graphene quantum dots (GQDs) are emerging as new alternatives due to their excellent properties, including high photoluminescence, low photobleaching, high biocompatibility and low toxicity. C-dots avoid the use of heavy metals present in semiconductor quantum dots, which have raised important health and

• . Results and Discussion Absorption and photoluminescence characterization of C-dots The C-dots were synthesized using spices as starting material through a green one-pot hydrothermal method that involves pyrolysis, carbonization and passivation [33][34][35], with no need to add surface passivation agents

• months without any loss of their optical properties. Typically, C-dots exhibit an interesting excitation-dependent photoluminescence, entirely different from other luminescent materials such as semiconductor quantum dots, gold or silver nanoclusters. This luminescence is attributed to defect states of

Influence of the preparation method on the photocatalytic activity of Nd-modified TiO₂

• Patrycja Parnicka,
• Paweł Mazierski,
• Tomasz Grzyb,
• Wojciech Lisowski,
• Ewa Kowalska,
• Bunsho Ohtani,
• Adriana Zaleska-Medynska and
• Joanna Nadolna

Beilstein J. Nanotechnol. 2018, 9, 447–459, doi:10.3762/bjnano.9.43

• that for photocatalysts obtained by the SHT method the agglomerates are a bit smaller. Optical and photoluminescence properties To study the optical absorption properties of the as-prepared photocatalysts, diffuse reflectance spectra (DRS) in the range of 200–850 nm were investigated, and the results

• states of 4G7/2 and 2K13/2, 4G5/2 and 2G7/2, 4S3/2 and 4F7/2, 4F5/2 and 2H9/2 [30][37]. In all of the studied Nd-modified samples, the intensity of these absorption bands was similar. To understand the rate of electron–hole recombination, photoluminescence (PL) spectroscopy was applied. Figure 4 shows

• the PL spectra of pristine and Nd-modified TiO2 under excitation by light at λex = 315 nm. The photoluminescence spectra show a weak broad emission band with a maximum intensity at around 350–700 nm. Khalid et al. [38] and Raja et al. [39] reported that emission in that range is characteristic for

Facile synthesis of ZnFe₂O₄ photocatalysts for decolourization of organic dyes under solar irradiation

• Arjun Behera,
• Debasmita Kandi,
• Sanjit Manohar Majhi,
• Satyabadi Martha and
• Kulamani Parida

Beilstein J. Nanotechnol. 2018, 9, 436–446, doi:10.3762/bjnano.9.42

• photoluminescence (PL) emission spectra were investigated by a JASCO-FP-8300 fluorescence spectrometer with an excitation wavelength of 330 nm. The chemical composition and vibrational modes of the ZFO samples were analysed by JASCO FTIR-4600. A ZEISS SUPRA 55 was used for FESEM analysis. Morphology and

• separation process and the fate of photoinduced electron–hole pair. Figure 5 shows the photoluminescence spectra of the ZFO samples calcined at different temperatures. The most intense PL band of ZFO is centred around 400–410 nm when excited at 330 nm. PL spectra with low-emission intensity correlate with a

• -500. Photoluminescence spectra of ZFO samples excited at 330 nm. FTIR spectra of ZFO samples. Linear-sweep voltammograms of ZFO-400 to ZFO-700 (a) under dark conditions, (b) under visible-light illumination. Mott–Schottky plot yielding the flat-band potential of ZFO-500. Nyquist plot of ZFO-400 to ZFO

Sugarcane juice derived carbon dot–graphitic carbon nitride composites for bisphenol A degradation under sunlight irradiation

• Lan Ching Sim,
• Jing Lin Wong,
• Chen Hong Hak,
• Jun Yan Tai,
• Kah Hon Leong and
• Pichiah Saravanan

Beilstein J. Nanotechnol. 2018, 9, 353–363, doi:10.3762/bjnano.9.35

• revealed new signals for carbonyl and carboxyl groups originating from the CDs in CD/g-C3N4 composites while X-ray diffraction (XRD) results showed distortion of the host matrix after incorporating CDs into g-C3N4. Both analyses signified the interaction between g-C3N4 and CDs. The photoluminescence (PL

• diffuse reflectance spectra (UV–vis DRS) results. Although the CDs did not display upconversion photoluminescence (UCPL) properties, the π-conjugated CDs served as a photosensitizer (like organic dyes) to sensitize g-C3N4 and injected electrons to the conduction band (CB) of g-C3N4, resulting in the

• graphitic carbon [1]. CDs possess upconversion photoluminescence (UCPL) properties [2] and are able to harvest long wavelength light in the visible and near infrared (NIR) region [3][4], rendering them promising candidates as photosensitizers in photocatalysis. Nevertheless, the reported preparation method

Dopant-stimulated growth of GaN nanotube-like nanostructures on Si(111) by molecular beam epitaxy

• Alexey D. Bolshakov,
• Alexey M. Mozharov,
• Georgiy A. Sapunov,
• Igor V. Shtrom,
• Nickolay V. Sibirev,
• Vladimir V. Fedorov,
• Evgeniy V. Ubyivovk,
• Maria Tchernycheva,
• George E. Cirlin and
• Ivan S. Mukhin

Beilstein J. Nanotechnol. 2018, 9, 146–154, doi:10.3762/bjnano.9.17

• and possess high crystal quality. We propose a theoretical model of the novel nanostructure formation which includes the role of the dopant Si. Some of the Si-doped samples were studied with the photoluminescence (PL) technique. The analysis of the PL spectra shows that the highest value of donor

• knowledge, in this paper we demonstrate for the first time self-organized dopant-activated growth of high crystal quality GaN NT-like nanostructures on Si(111) substrates covered with a thin AlN buffer layer created using the MBE technique. The synthesized nanostructures were studied with photoluminescence

• Si doping on the photoluminescence (PL) spectra of the synthesized structures. In the Table 1 one can find a description of the studied samples. Figure 3 shows the PL spectra from samples with various doping levels (samples 1, 3, 4 and 12). The spectra were obtained at a temperature of 10 K by using

Co-reductive fabrication of carbon nanodots with high quantum yield for bioimaging of bacteria

• Jiajun Wang,
• Xia Liu,
• Gesmi Milcovich,
• Tzu-Yu Chen,
• Edel Durack,
• Sarah Mallen,
• Yongming Ruan,
• Xuexiang Weng and
• Sarah P. Hudson

Beilstein J. Nanotechnol. 2018, 9, 137–145, doi:10.3762/bjnano.9.16

• for bioimaging purposes thanks to their fluorescent features. In this context, the quantum yield (QY) is one of the most important features for C-dot performance. Although, at present, the actual mechanism of the photoluminescence of C-dots is still an open debate among researchers [6][7][8

PTFE-based microreactor system for the continuous synthesis of full-visible-spectrum emitting cesium lead halide perovskite nanocrystals

• Chengxi Zhang,
• Weiling Luan,
• Yuhang Yin and
• Fuqian Yang

Beilstein J. Nanotechnol. 2017, 8, 2521–2529, doi:10.3762/bjnano.8.252

• photoluminescence emission in the range of 450–700 nm. For the same precursor concentrations, the photoluminescence emission peak generally increases with increasing reaction temperature, revealing a controllable temperature effect on the photoluminescence characteristics of the synthesized nanocrystals. For

• with applications ranging from displays and optoelectronic devices. Keywords: cesium lead halide; microreactor system; nanocrystals; perovskite; photoluminescence; Introduction Colloidal semiconductor nanocrystals, also known as quantum dots (QDs), have great potential in a variety of applications

• have constructed a PTFE-based microreactor system in which CsPbX3 nanocrystals are continuously synthesized. The fluorescence characteristics of the CsPbX3 nanocrystals can be tuned via the changes in the synthesis temperature and the halide composition (Br, I). The photoluminescence (PL) emission

Laser-assisted fabrication of gold nanoparticle-composed structures embedded in borosilicate glass

• Nikolay Nedyalkov,
• Mihaela Koleva,
• Nadya Stankova,
• Rosen Nikov,
• Mitsuhiro Terakawa,
• Yasutaka Nakajima,
• Lyubomir Aleksandrov and
• Reni Iordanova

Beilstein J. Nanotechnol. 2017, 8, 2454–2463, doi:10.3762/bjnano.8.244

• noble metal nanoparticles into dielectric oxide and polymer matrices results in a large increase of the third-order nonlinear optical susceptibility, an enhancement of the photoluminescence signal from the matrix, a metamaterial-like behavior, and the possibility of modifying the conductivity of the

Changes of the absorption cross section of Si nanocrystals with temperature and distance

• Michael Greben,
• Petro Khoroshyy,
• Sebastian Gutsch,
• Daniel Hiller,
• Margit Zacharias and
• Jan Valenta

Beilstein J. Nanotechnol. 2017, 8, 2315–2323, doi:10.3762/bjnano.8.231

• and multilayer structures with variable thickness of oxide barriers is determined via a photoluminescence (PL) modulation technique that is based on the analysis of excitation intensity-dependent PL kinetics under modulated pumping. We clearly demonstrate that roughly doubling the barrier thickness

• Si NCs cannot be considered as independent on experimental conditions and sample parameters. Keywords: absorption cross section; average lifetime; nanocrystal distance; photoluminescence decay; silicon nanocrystals; Introduction For decades, silicon – an abundant, nontoxic material with high

• determination by two completely independent methods including a photoluminescence (PL) modulation technique [10]. In this work, we employ this procedure to analyze the dependence of the ACS of ML structures on mainly two important parameters: inter-nanocrystal distance and temperature. It will be shown that

Hydrothermal synthesis of ZnO quantum dot/KNb₃O₈ nanosheet photocatalysts for reducing carbon dioxide to methanol

• Xiao Shao,
• Weiyue Xin and
• Xiaohong Yin

Beilstein J. Nanotechnol. 2017, 8, 2264–2270, doi:10.3762/bjnano.8.226

• images were obtained with a Tecnai G2 F20 instrument. The UV–vis diffuse reflectance spectra were captured by a Shimadzu UV–2550 UV–vis spectrophotometer using BaSO4 as a reference in the wavelength region of 200–800 nm. Photoluminescence (PL) spectra were measured at room temperature on a Renishaw 1000

• nanosheets were recycled three times. This shows that the activity of the materials slowly declines but the formation rate of methanol was maintained at around 1500 μmol/g/h. Photoluminescence (PL) spectroscopy was used to trace the migration and capture of photogenerated electrons and holes from the as

• nanosheets with different amounts of ZnO quantum dot (QD) loadings: (0) pure KNb3O8; (1) 1 wt % ZnO QDs; (2) 2 wt % ZnO QDs; (3) 3 wt % ZnO QDs; (4) 4 wt % ZnO QDs. Trials showing the recyclability of the 2 wt % ZnO quantum dot/KNb3O8 nanosheet composite photocatalyst. Photoluminescence (PL) spectra of the 2

Substrate and Mg doping effects in GaAs nanowires

• Perumal Kannappan,
• Nabiha Ben Sedrine,
• Jennifer P. Teixeira,
• Maria R. Soares,
• Bruno P. Falcão,
• Maria R. Correia,
• Nestor Cifuentes,
• Emilson R. Viana,
• Marcus V. B. Moreira,
• Geraldo M. Ribeiro,
• Alfredo G. de Oliveira,
• Juan C. González and
• Joaquim P. Leitão

Beilstein J. Nanotechnol. 2017, 8, 2126–2138, doi:10.3762/bjnano.8.212

• ; photoluminescence; Introduction In recent years, semiconductor nanowires have attracted a great deal of interest as building blocks for a new generation of electronic and optoelectronic devices, namely, batteries, biological and chemical sensors, thermoelectric devices, laser diodes, photo detectors, integrated

• -gate field effect transistors (FETs) allowed the estimation of the free hole concentration and the electrical mobility. The photoluminescence (PL) measurements revealed a few radiative transitions. The PL dependence on the excitation power and temperature was performed. The non-radiative de-excitation

Preparation and characterization of polycarbonate/multiwalled carbon nanotube nanocomposites

• Claudio Larosa,
• Niranjan Patra,
• Marco Salerno,
• Lara Mikac,
• Remo Merijs Meri and
• Mile Ivanda

Beilstein J. Nanotechnol. 2017, 8, 2026–2031, doi:10.3762/bjnano.8.203

• observed for the composition with 3 wt % loading of MWCNTs. This absorption is characteristic of individually dispersed MWCNTs, whereas strongly bundled MWCNTs do not show an absorption band in 200–1200 nm wavelength region as their photoluminescence is quenched or the carriers are tunneling between the

Synthesis and functionalization of NaGdF₄:Yb,Er@NaGdF₄ core–shell nanoparticles for possible application as multimodal contrast agents

• Dovile Baziulyte-Paulaviciene,
• Vitalijus Karabanovas,
• Marius Stasys,
• Greta Jarockyte,
• Vilius Poderys,
• Simas Sakirzanovas and
• Ricardas Rotomskis

Beilstein J. Nanotechnol. 2017, 8, 1815–1824, doi:10.3762/bjnano.8.183

• ) spectroscopy. Scanning electron microscopy (SEM), powder X-ray diffraction (XRD), photoluminescence (PL) spectra and magnetic resonance (MR) T1 relaxation measurements were used to characterize the size, crystal structure, optical and magnetic properties of the core and core–shell nanoparticles. Moreover

Uptake and intracellular accumulation of diamond nanoparticles – a metabolic and cytotoxic study

• Antonín Brož,
• Lucie Bačáková,
• Pavla Štenclová,
• Alexander Kromka and
• Štěpán Potocký

Beilstein J. Nanotechnol. 2017, 8, 1649–1657, doi:10.3762/bjnano.8.165

• materials, for example, films for potential implant coatings [13]. Nanodiamond-based drug delivery has been mainly developed for advanced tumour therapies and for localized drug delivery [3][14]. Due to their stable and controllable photoluminescence, NDs are also highly promising for advanced photonic and

• cytokineses, and most of them survive until the end of the video sequence. Only two or three cell death events can be recognized in the video. Photoluminescence of diamond nanoparticles Figure 5 shows fluorescence phase contrast images of osteoblasts and photoluminescent NDs (AR-40, 100 µg/mL, 30 µg/cm2) grown

• for 3 and 7 days. The images reveal the presence of NDs in the cells. The red photoluminescence signal around the outside of the cell nuclei indicate that the NDs could not penetrate the nuclear envelope and stay in the cytoplasm. A certain amount of NDs are present outside the cells, probably in the

Two-dimensional carbon-based nanocomposites for photocatalytic energy generation and environmental remediation applications

• Suneel Kumar,
• Ashish Kumar,
• Ashish Bahuguna,
• Vipul Sharma and
• Venkata Krishnan

Beilstein J. Nanotechnol. 2017, 8, 1571–1600, doi:10.3762/bjnano.8.159

Light-induced magnetoresistance in solution-processed planar hybrid devices measured under ambient conditions

• Sreetama Banerjee,
• Daniel Bülz,
• Danny Reuter,
• Karla Hiller,
• Dietrich R. T. Zahn and
• Georgeta Salvan

Beilstein J. Nanotechnol. 2017, 8, 1502–1507, doi:10.3762/bjnano.8.150

• in photoluminescence caused by the diffusion of oxygen/water in TIPS-pentacene films in the HED-TIE devices to be reversible [12] and that the recovery is much faster under nitrogen purging and single-wavelength illumination. To verify the role of the diffusion of water molecules into the TIPS

Calcium fluoride based multifunctional nanoparticles for multimodal imaging

• Marion Straßer,
• Joachim H. X. Schrauth,
• Sofia Dembski,
• Daniel Haddad,
• Bernd Ahrens,
• Stefan Schweizer,
• Bastian Christ,
• Alevtina Cubukova,
• Marco Metzger,
• Heike Walles,
• Peter M. Jakob and
• Gerhard Sextl

Beilstein J. Nanotechnol. 2017, 8, 1484–1493, doi:10.3762/bjnano.8.148

• different imaging techniques, such as photoluminescence (PL) microscopy and magnetic resonance imaging (MRI), open new possibilities for medical imaging, e.g., in the fields of diagnostics or tissue characterization in regenerative medicine. The focus of this study is on the synthesis and characterization

• nanoparticles; magnetic resonance imaging (MRI); multifunctional nanoparticles; multimodal imaging; photoluminescence; Introduction In recent years, medical imaging has become an important approach in the fields of diagnostics, therapy and regenerative medicine. Besides the classical technology of X-ray

• carried out by using transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis, inductively coupled plasma optical emission spectrometry (ICP-OES), and photoluminescence (PL) spectroscopy. The capability of these NPs to be used as positive CAs for MRI was also investigated. In addition, the

Nano-engineered skin mesenchymal stem cells: potential vehicles for tumour-targeted quantum-dot delivery

• Liga Saulite,
• Dominyka Dapkute,
• Karlis Pleiko,
• Ineta Popena,
• Simona Steponkiene,
• Ricardas Rotomskis and
• Una Riekstina

Beilstein J. Nanotechnol. 2017, 8, 1218–1230, doi:10.3762/bjnano.8.123

• QDs indicate their great potential in cancer diagnostics. The photoluminescence spectrum of carboxyl QD655 makes them ideal candidates for cancer theranostics as it overlaps with the optical transparency window of biological tissue [11]. Additionally, large and easily altered surfaces facilitate

AgCl-doped CdSe quantum dots with near-IR photoluminescence

• Pavel A. Kotin,
• Sergey S. Bubenov,
• Natalia E. Mordvinova and
• Sergey G. Dorofeev

Beilstein J. Nanotechnol. 2017, 8, 1156–1166, doi:10.3762/bjnano.8.117

• nanoparticles possess an intensive near-IR photoluminescence ranging up to 0.9 eV (ca. 1400 nm). In this article, we explain the reasons for the formation of the ellipsoidal nanoparticles as well as the peculiarities of the process. The structure, Ag content, and optical properties of quantum dots are also

• investigated. The optimal conditions for maximizing both the reaction yield and IR photoluminescence quantum yield are found. Keywords: Ag doping; CdSe quantum dots; doped semiconductor nanocrystals; IR photoluminescence; tetrapods; Introduction Colloidal quantum dots (QDs) have attracted considerable

• devices. CdSe QDs deserve special attention because of their bright photoluminescence (PL), photostability, and a considerable number of methods for their synthesis. For many of the practical applications of QDs infrared PL (IR-PL) is very important: for the fabrication of optical fibers, lasers

ZnO nanoparticles sensitized by CuInZn_xS_2+x quantum dots as highly efficient solar light driven photocatalysts

• Florian Donat,
• Serge Corbel,
• Halima Alem,
• Steve Pontvianne,
• Lavinia Balan,
• Ghouti Medjahdi and
• Raphaël Schneider

Beilstein J. Nanotechnol. 2017, 8, 1080–1093, doi:10.3762/bjnano.8.110

• was added and the mixture was incubated for 50 min at room temperature in the dark. The photoluminescence spectra were recorded in order to estimate the formation of 2-OH-DST (λex = 300 nm). The quantification of •OH production was conducted according to the method we recently described [42

• production of 1O2 was evaluated by measuring the photoluminescence of SOSG–endoperoxide (SOSG-EP) (λex = 480 nm and λem = 525 nm) [42]. Instruments and characterization Transmission electron microscopy (TEM) investigations were performed with a JEOL ARM 200F – Cold FEG TEM/STEM (point resolution 0.19 nm in

• spectrophotometer. The photoluminescence (PL) spectra were recorded on a Horiba Fluoromax-4 Jobin Yvon spectrofluorimeter. The diffuse reflectance spectra (DRS) were recorded on a Shimadzu 2600 UV–vis spectrophotometer. BaSO4 powder was used as a standard for baseline measurements and spectra were recorded in a