PL Emission Bands Research Articles

Influence of annealing temperature and laser irradiation on the structural, optical, and photoluminescence characteristics of Ni2O3/SnO2 nanocomposites for perspective applications

In this study, a new approach methodology is employed to modify the structural, optical, and photoluminescence properties of Ni2O3/SnO2(NO/TO) nanocomposites. The effects of temperature and laser irradiation on a specific system were analyzed and described using XRD, XPS, and TEM. The diffraction patterns indicate the presence of two distinct phases within the NO/TO system. The XPS results reveal a robust underlying interaction between Ni2O3 and SnO2, exhibited by the observed shifts in the peak positions of Ni 2p, Sn 3d, and O 1 s. The TEM images demonstrate the formation of hexagonal and half-hexagonal forms with varying orientations, as well as the emergence of elongated tetragonal shapes, upon increasing the temperature to 900 °C. the notable enhancement in light absorption, with the absorption bands spanning a wide range in the UV–vis spectra, specifically from approximately 300 nm to around 800 nm in the near-infrared (NIR) region. The broad range of PL emission bands identified by this mixture of nanoparticles, expanding from the UV to the near and intermediate IR regions, demonstrated that NO/TO nanocpomposites are considerably defective. The NO/TO nanocomposites exhibit efficient multi-color band emissions at ambient conditions, rendering them promising contenders for deployment in optoelectronic nanodevices, including blue, yellow, and white band emission light-emitting diodes and NIR luminescence bioimaging.

Mesoporous Ag@WO3 core–shell, an investigation at different concentrated environment employing laser ablation in liquid

In this study, silver-tungsten oxide core–shell nanoparticles (Ag–WO3 NPs) were synthesized by pulsed laser ablation in liquid employing a (1.06 µm) Q-switched Nd:YAG laser, at different Ag colloidal concentration environment (different core concentration). The produced Ag–WO3 core–shell NPs were subjected to characterization using UV–visible spectrophotometry, X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive spectroscopy, electrical analysis, and photoluminescence PL. The UV–visible spectra exhibited distinct absorption peaks at around 200 and 405 nm, which attributed to the occurrence of surface Plasmon resonance of Ag NPs and WO3 NPs, respectively. The absorbance values of the Ag–WO3 core–shell NPs increased as the core concentrations rose, while the band gap decreased by 2.73–2.5 eV, The (PL) results exhibited prominent peaks with a central wavelength of 456, 458, 458, 464, and 466 nm. Additionally, the PL intensity of the Ag–WO3-NP samples increased proportionally with the concentration of the core. Furthermore, the redshift seen at the peak of the PL emission band may be attributed to the quantum confinement effect. EDX analysis can verify the creation process of the Ag–WO3 core–shell nanostructure. XRD analysis confirms the presence of Ag and WO3 (NPs). The TEM images provided a good visualization of the core-spherical shell structure of the Ag–WO3 core–shell NPs. The average size of the particles ranged from 30.5 to 89 (nm). The electrical characteristics showed an increase in electrical conductivity from (5.89 × 10−4) (Ω cm)−1 to (9.91 × 10−4) (Ω cm)−1, with a drop in average activation energy values of (0.155 eV) and (0.084 eV) at a concentration of 1.6 μg/mL of silver.

Electron spin resonance and photoluminescence studies of Co/Mg co‐doped ZnO nanoparticles

AbstractZn0.95−xMg0.05CoxO (x = 0.01–0.05 with an increment of 0.01) nanoparticles were synthesized by using the sol–gel technique to analyze structural and magnetic properties. The single phase was observed in the X‐ray diffraction measurements. To examine the surface morphology, elemental compositions, crystal quality, defect type, density, and magnetic behavior of the nanoparticles, SEM, energy dispersive X‐ray analysis (EDX), PL, and ESR were used, respectively. The PL has ultraviolet and a broad emission band including violet and a blue spectral region corresponding to the defect‐related and excitonic emissions. These emissions were strongly dependent on the synthesize condition and doping element and ratio. The effect of cobalt concentration on the line widths of pike to pike (ΔHPP) and the g‐factor of ESR spectra were investigated. By comparing the results of the ESR and PL measurements, it was determined which defect with a given g‐factor was responsible for the corresponding PL emission band. In addition, ESR spectra of Mg/Co co‐doped ZnO nanoparticles with different cobalt concentrations recorded at room temperature were presented. Since Mg/Co co‐doped ZnO nanoparticles reveal ferromagnetism at RT, they could be an appropriate material for new devices in spin‐based technologies.

Study of the properties of zirconia nanoparticles/zinc oxide films composites: Comparation to thermally treated samples

The aim of this study was to evaluate the effect the thermal treatment on the structural and optical properties of zinc oxide (ZnO) films and zirconia nanoparticles/zinc oxide film composites (ZrO2-nps/ZnO-films: Comp). X-ray diffraction (XRD) measurements indicated that structural properties of the ZnO and the ZrO2-nps/ZnO-films: Comp were improved after the thermal treatment at 500 °C for 24 h in air atmosphere. Field emission scanning electron microscopy images showed that the thermal treatment promoted a smoother surface in the ZnO films, and in the ZrO2-nps/ZnO-films: Comp it induced partial agglomeration of the ZrO2-nps. High resolution transmission electron microscopy confirmed the presence and the crystalline nature of the ZrO2-nps. The band gap calculated by UV–Vis measurements exhibited an opposite trend. In ZnO films the band gap was reduced after thermal treatment whereas in ZrO2-nps/ZnO-films: Comp the band gap increased after this posttreatment. PL measurements supported the XRD results due to the wide PL emission band in the visible region, which was partially splitted after the thermal treatment. In fact, the PL visible band corresponding to the ZrO2-nps/ZnO-films: Comp was weakened after the thermal treatment. Fourier transformed infrared spectra of ZnO films without and with thermal treatment were very similar, exhibiting the characteristic Zn-O vibration and a carboxylate band. However, for ZrO2-nps/ZnO-films: Comp the carboxylate band was almost imperceptible.

Synthesis, characterization, and photophysical properties of dicyanoarylamine‐based semi‐aromatic polymers

AbstractIntroductionFluorescent high‐performance polymers have been extensively used in designing optoelectronic devices due to their low cost, excellent thermal stability, high mechanical strength, low flammability, good chemical and radiation resistance, and good electronic properties. While conventional organic luminophores fluoresce strongly in dilute solutions, they suffer from undesirable aggregation‐caused quenching in concentrated solutions and in the solid state due to extensive π‐π stacking interactions and formation of delocalized excitons or excimers. This phenomenon leads to non‐radiative decay thus, decreased fluorescence emission of the material in the solid film state, which significantly limits their real‐world application as solid light‐emitting materials.ObjectivesTo develop new high‐performance polymers with high photo luminescent efficiency, good processability, film‐forming properties, which could potentially be used in the fabrication of optoelectronic devices.MethodsThe preparation of the polyimide DiCN‐PI was carried out by a one‐step, high‐temperature solution imidization method. In this procedure, 1,2,4,5‐cyclohexanetetracarboxylic dianhydride and the diamine were polymerized in 1‐methyl‐2‐pyrrolidinone and γ‐butyrolactone co‐solvent at 180°C for 15 hours in the presence of isoquinoline as catalyst. On the other hand, polyamide DiCN‐PA was synthesized according to the direct phosphorylation polycondensation technique described by Yamazaki from diamine and trans‐1,4‐cyclohexanedicarboxylic acid using triphenyl phosphite and pyridine as condensing agents.Results and DiscussionBoth polymers were soluble in several polar aprotic solvents and exhibited useful levels of thermal stability. The polymers were emissive with PL emission bands around 555 (bluish‐green) and 498 (cyan) nm in dilute 1‐methyl‐2‐pyrrolidinone solutions for polyimide and polyamide, respectively. In the solid film state, the polymers emit light green and yellow colors, which simulate the PL behavior of their aggregated states, thereby demonstrating aggregation‐induced fluorescence changes.ConclusionsThese results indicate that the incorporation of bulky dicyanoarylamine moiety and alicyclic monomer units into the rigid polymer backbones effectively disrupted the planarity of the chain packing which resulted to the fluorescent high‐performance polymers with desired properties for potential optoelectronic applications.

Detailed Study of the Correlation between Cross-Linking of Thick SU-8 and UV-NIR Optical Transmission/Photoluminescence Spectroscopy.

SU-8 polymers are promising materials for various applications due to their low cost, excellent thermal stability, and outstanding mechanical properties. Cross-linking of SU-8 is a crucial process that determines the properties of the materials. This study investigates the effect of cross-linking of free-standing SU-8 films on optical transmission and PL emission under various curing conditions. Our findings show that an increase in the cross-linking density reduces optical transmission and causes a red shift of the PL emission band peaks. By directly measuring the optical response of the isolated SU-8, we remove any uncertainty due to the substrate's presence. Moreover, we show that optical transmission and PL spectroscopy are two non-distractive techniques that can be employed to monitor the curing of the SU-8. This finding enhances our understanding of the cross-linking process in SU-8 and paves the way to further enhance the properties of the SU-8 polymer for various electronics and optoelectronics applications.

Effect of silica encapsulation on the stability and photoluminescence emission of FAxCs1-xPbX3 quantum dots for white mini light emitting diodes

Development of wide-color gamut white light-emitting diodes (WLEDs) for displays, with nitride-based phosphors and conventional core-shell quantum dots (QDs) such as InP, CdSe, and all-inorganic CsPbI3 perovskite quantum dots due to their excellent optoelectronic properties performance, is an excellent candidate for new optoelectronic applications.However, in backlight applications, the color gamut of perovskite quantum dots will be reduced due to the matching degree of color filter, which will limit its application in wide color gamut. To address these issues, in this paper, we propose a novel approach, namely, formamidine acetate (FA+) cationic doping, in CsPbI3 system synthesized at room temperature by organic-inorganic ligand passivation method which can effectively maintain structural stability. At the same time, the PL emission band of CsPbI3 is increased by doping FA + cations and the color gamut range is improved. We will discuss this change in detail, and quantum dot films using spin coating method can be maintained for a month in atmospheric conditions. For practical applications, the color gamut range can reach 133%. Therefore, our proposed perovskite quantum dots, FAxCs1-xPbI3, have great potential for application in wide color gamut displays.

Effect of ZnS nanoparticles on the spectroscopic transitions of Ho3+ ions in sol-gel silica matrix

ZnS NPs and Ho3+ co-doped silica matrices are prepared by room temperature sol-gel method. The fabricated matrices are characterized structurally by X-ray diffractometry, Transmission electron microscopy, Energy dispersive X-ray analysis and Fourier transform infrared spectroscopy. Structural studies reveal the presence of ZnS NPs in the Ho3+ co-doped silica matrices. Judd Ofelt analysis of UV–Visible absorption spectra shows that the phenomenological Judd Ofelt intensity parameters Ωt, which illustrate the intensities for transitions in lanthanides and actinides in solids as well as solutions follow the trend Ω2>Ω4>Ω6. Enhancement in the Ω2 parameter with ZnS NP concentration indicates higher asymmetry and a stronger covalent environment of Ho3+ ions in the studied matrix, compared to some popular hosts. The four distinct PL emission bands of Ho3+ observed in the studied matrices show a strong dependence on ZnS NP concentration, with 0.67 M of ZnS as the optimum concentration. The enhancement in the PL emissions with ZnS NPs is attributed to the network modification and sensitization of Ho3+ ions by the NPs. Sensitization through energy transfer also increases the lifetime of the excited state, as observed from the PL decay study. The decrease of PL emission beyond optimum ZnS concentration is most likely due to the self-quenching of ZnS NPs. The upconversion study shows enhancement in Ho3+ luminescence up to 14 times with ZnS co-doping; indicating the viability of the fabricated matrix for their application in UC devices as well.

Chemical bath deposition synthesis of Dy2(CO3)3, and their evolution to Dy2O3 transition

Dy2(CO3)3 (dysprosium carbonate) nanocrystals, are successfully prepared at 60 °C, applying Chemical Bath Deposition technique. The powders are thermal annealing temperature (TAT) of 300 °C, 500 °C, 700 °C and 900 °C in air atmosphere. By XRD patterns, Dy2(CO3)3 where identified in the orthorhombic-phase. Structural evolution is observed for Dy2(CO3)3→Dy2O3 transition by correlating interplanar distance and grain size and Urbach energy tails, is applied to extract information on crystalline defects. The DSC experimental curve, shows a weight loss and a slight weight loss before ∼450 ◦C, indicating the absence of absorbed water or other polutants. The optical study in the %T, %R, Absorbance and d(D.O)/dE are investigated, the following optical responses are recorded: The non-hypersensitive 4F9/2→6H15/2 electronic intra-transitions (4fs→4fs) in Dy3+ cation being a magnetic dipole transition is insensitive to environment. Intense absorption band: 6H15/2, 6H11/2→6H9/2 is recorded at UV-region. Dy2O3(s) show absorption bands located at ∼457 nm (∼2.71 eV), assigned to Dy3+ cation of 4F9/2⟶6H15/2 electronic intra-transition. The dOD/dE vs. Energy (eV) spectra shows absorption bands situated at ∼324 nm (∼3.82 eV), ∼348 nm (∼3.56 eV), ∼363 nm (∼3.41 eV), ∼386 nm (∼3.21 eV) and ∼399 nm (∼3.10 eV) to 6H15/2→4M17/2, 6H15/2→6P7/2, 6H15/2→6P5/2, 6H15/2→4K17/2 to 4fs→4fs electronic intra-transitions of Dy3+ cation. The PL emission band located at UV-Vis region, are overlapped with the 4fs→4fs electronic intratransitions, typical of the Dy3+ cation, which are deconvoluted and associated with intrinsic crystalline defects.

Transforming exciton dynamics in perovskite nanocrystal through Mn doping.

Zn-alloyed CsPb(Cl/Br)3 perovskite nanocrystals (PNCs) have been synthesized and used as a model system for Mn doping in order to understand the effect of Mn doping on exciton dynamics. While keeping the PL emission maximum and PLQY of both PNC samples nearly the same, the radiative decay rate of the host band decreases ∼6.5 times and the non-radiative decay rate increases ∼2.5 times upon Mn doping. Unlike reports in the literature in which the dopant emission decreases to near-zero, in the present case we observe ∼5.5-fold enhancement of the integrated PL intensity of the dopant emission when the temperature decreases from 290 K to 190 K. Interestingly, the FWHM of the host PL emission band increases with a decrease in temperature from 290 K to 190 K. A higher value of phonon energy in PNC2 (58 ± 2 meV) in comparison to CsPbBr3 has been noted. The low magnitude of the Huang-Rhys factor indicates less electron phonon coupling for the Mn-doped PNC system. Temperature-dependent dopant PL decay exhibits biexponential decay behaviour with time constants τ1 = 450-540 μs and τ2 = 1.1-1.2 ms. With a decrease in temperature from 290 K to 190 K, the amplitude of the faster component decreases from 80% to 60%; concomitantly, the amplitude of the slower component increases from 20% to 40%. Ultrasensitive single-particle spectroscopic analyses reveal that, although the probability density distributions (PDDs) of the durations of both ON and OFF events of PNC1 could be fitted with a truncated inverse power law (TIPL), however, for PNC2, both PDDs could be fitted with an inverse power law (IPL). A comparatively lower value of the power law exponent mON indicates a higher probability of longer ON events for PNC1 than for PNC2. Truncation in the PDDs of both ON and OFF events has been observed for PNC1, but not in the PDDs of either ON or OFF events for PNC2. The presence of shallow trap states is responsible for the truncation for PNC1, whereas the presence of deep dopant states does not allow truncation in the host PL emission of PNC2. All these observations clearly demonstrate that Mn doping transforms the host PL exciton dynamics for Zn-alloyed Mn-doped CsPb(Cl/Br)3 PNCs very significantly.

Structural and luminescence property evaluation of Sm3+ activated orange light emitting Li7La3Zr2O12 phosphors

• Synthesis of cubic blue light emitting pure LLZO and orange light emitting LLZO: xSm 3+ (x=0.1, 0.3, 0.5, 0.7 and 0.9 M.W%) phosphors by solid state reaction method. • The optical energy band gap values of synthesised phosphors for pure and Sm 3+ doped LLZO were calculated to be 4.140 eV and 3.972 eV, respectively. • The strongest PL emission band observed at 602 nm was assigned to 4 G 5/2 → 6 H 7/2 transition in orange region under the ultraviolet excitation wavelength of 408 nm. • The blue and orange light emission was confirmed by CIE chromaticity X, Y coordinates. • Color purity and CCT value of 0.5 MW% Sm 3+ doped LLZO phosphor was 85.9% and 2227 K, respectively. Samarium (Sm) activated Li 7 La 3 Zr 2 O 12 (LLZO) phosphors were synthesized by solid state reaction method. Crystal structure of Sm 3+ doped LLZO was investigated using X-ray diffraction and Raman spectroscopy analysis. From Raman spectra, the presence of characteristic Raman peak at 110 cm -1 confirms the formation of LLZO. The Raman peaks present at 345 cm -1 and 125 cm -1 correspond to T 2g Raman mode of vibration and E g mode of vibration, respectively. The optical energy band gap values of synthesised phosphors obtained from UV-Vis spectroscopy for pure and Sm 3+ doped LLZO were calculated to be 4.140 eV and 3.972 eV, respectively. Microstructure and selected area diffraction (SAED) pattern of phosphor was observed by High Resolution Transmission Emission Electron Microscope. Using an excitation wave length of 209 nm,blue emission was observed for pure LLZO and the chromaticity coordinate was found to be at (x=0.1636, y=0.0123). Sm 3+ doped phosphors showed orange light emission under 408 nm excitation due to transition of 4 G 5/2 - 6 H 7/2. as observed from the Commission Internationale de l’Eclairage (CIE) chromatic coordinate graph. The maximum intensity of emission was observed in 0.5% Sm 3+ doped LLZO with the calculated color purity and correlated color temperature of 85.9% and 2229k, respectively.

Carrier dynamics in (Ga,In)(Sb,Bi)/GaSb quantum wells for laser applications in the mid-infrared spectral range

We present experimental studies on low-temperature (T={4.2}hbox { K}) carrier dynamics in (Ga,In)(Sb,Bi)/GaSb quantum wells (QWs) with the nominal In content of 3.7% and the Bi ranging from 6 to 8%. The photoreflectance experiment revealed the QW bandgap evolution with -{33}pm {1}hbox { meV}/hbox {at} % Bi, which resulted in the bandgap tunability roughly between 629 and {578}hbox { meV}, setting up the photon emission wavelength between 1.97 and {2.2},upmu hbox {m}. The photoluminescence experiment showed a relatively small 3–10hbox { meV} Stokes shift regarding the fundamental QW absorption edge, indicating the exciton localisation beneath the QW mobility edge. The localised state’s distribution, being the origin of the PL, determined carrier dynamics in the QWs probed directly by the time-resolved photoluminescence and transient reflectivity. The intraband carrier relaxation time to the QW ground state, following the non-resonant excitation, occurred within 3–25hbox { ps} and was nearly independent of the Bi content. However, the interband relaxation showed a strong time dispersion across the PL emission band and ranging nearly between 150 and {950}hbox { ps}, indicating the carrier transfer among the localised state’s distribution. Furthermore, the estimated linear dispersion variation parameter significantly decreased from Delta tau approx {20} to {10}hbox { ps}/hbox {meV} with increasing the Bi content, manifested the increasing role of the non-radiative recombination processes with Bi in the QWs.

Tunable photoluminescence properties of Dy3+ doped LLZO phosphors for WLED and dosimetry applications

Trivalent Dysprosium (Dy 3+ ) activated garnet structured Li 7 La 3 Zr 2 O 12 (LLZO) phosphors were synthesized by conventional solid state reaction method. The phase structure of the prepared Dy 3+ doped LLZO powders was confirmed by X-ray diffraction and Raman spectroscopy studies. Field Emission Scanning Electron Microscopy (FESEM) studies indicated a change in morphology and an increase in the area of the intergranular Li–Al–O liquid layer is observed with the increase of Li and dopant concentrations. Composition analysis of the prepared samples was examined by X-ray photoelectron spectroscopy (XPS) analysis. PL emission band observed at 579 nm was assigned to 4 F 9/2 - 6 H 13/2 transition in yellow region under the ultraviolet excitation wavelength of 351 nm. White light emission was confirmed by the Commission Internationale de L'Eclairage (CIE) chromatic coordinate graph. Thermoluminescence studies were carried out and the results indicated that the grown phosphors are suitable for industrial dosimetric applications where high doses are needed to be measured.

Sharp luminescent violet- and blue-emitting stable (Eu3+ → Eu2+: PPA):SiO2 sonogel hybrid glasses: Synthesis, structural and overall photophysical characterizations

Nanostructured Eu2O3:Polyphenylacetylene (Eu2O3:PPA) complexes prepared at different lanthanide content were synthesized as active ligand–to–metal charge–transfer (LMCT) systems. These phosphors were embedded into mesoporous a–SiO2 sonogel hosting networks at different dopant ratios to obtain luminescent (Eu2O3:PPA):SiO2 monolith glasses. The electroactive sonochemical medium of the colloidal sol–phase activates massive Eu3+→Eu2+ self–reduction processes along the polycondensation reaction of the doped emulsions, giving rise to sharp violet (407 nm) and blue (470 nm) PL–emission bands (FWHM ≤18 nm). The unusual violet–lines arise from the 4f65d1→4f7 transitions of Eu2+ ions to produce intense 6P7/2 → 8S7/2 emissions, while the blue–lines are ascribed to overlapping 5D2→7Fj (j = 0, 1) transitions of remanent Eu3+ ions assisted by LMCT and interionic energy transfers. The CIE coordinates of these composites lay within the light violet/blue region and the bandgap energy was reduced up to 2.16 eV for increasing Eu2O3 concentration. Our experimental approach shows that the Eu3+→Eu2+ process occurs at room temperature material processing, without the use of reducing atmospheres, stimulated UV photoreduction, or post–doping functionalization. Results suggest that guest–host redox interactions and Eu/SiO2 surface–assisted mechanisms are responsible for accomplishing a homogeneous self–reduction and the structuring of steady Eu2+–silicates. Extensive morphological, structural, linear and NLO spectroscopic characterizations, CIE–chromaticity, and energy bandgap evaluations, were performed to explore these novel nanostructured composites' physicochemical and photophysical properties, pointing out potential applications in tunable phosphor devices.

Electrochemical Sensor and luminescence applications of Chonemorpha fragrans leaf extract mediated ZnO/Ag nanostructures

ZnO: Ag (0–20 mol%) hexagonal nanostructures were prepared via the phyto-synthesis route using Chonemorpha fragrans leaf extract. The structure, morphology, and compositions of the as-formed product were characterized by powder X-ray diffraction (PXRD), Field Emission Scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), Surface-enhanced area diffraction (SEAD), and Raman spectroscopy. Further, prepared nanostructures were subjected to sensor and luminescence studies. PXRD pattern shows the formation of the hexagonal wurtzite system. The Rietveld refinement analysis is used to refine structural parameters. FESEM micrographs show the agglomeration of the nanoparticles. The TEM pictures reveal the hexagonal shaped nanoparticles. The average 30 - 35 nm ranged crystallite sizes were determined using Scherrer's method which is in good agreement with the TEM. An economical and naturally responsive strategy can be the use of plant extract in the synthesis of nanostructured products. Also, studies related to sensing of paracetamol were performed using ZnO: Ag (20 mol%) indicating that it is a promising electrode material for paracetamol sensing. The identified PL emission bands indicate favorable luminescence applications for ZnO: Ag nanopowders.

Emission features of Er3+ ions in an exotic SeO2 based glass system

In this work we have studied impact of SeO2 concentration on luminescence properties of 39PbO-(60-x)B2O3-xSeO2:1.0 Er2O3 ( 10 ≤ x ≤ 50) glass system. The structural analysis of the samples carried out by XRD, SEM indicated that the prepared samples are in amorphous phase. IR, Raman and XPS studies revealed increasing presence of isolated selenite [SeO3]2−groups and decreasing concentration of [SeO4]2−(selenate) groups with increasing content of SeO2 in the glass network. Optical absorption (OA) spectra revealed absorption bands due to 4I15/2 → 4F7/2, 9/2, 2H11/2, 4S3/2, 4I9/2, 11/2, 13/2 transitions of Er3+ ions. Using J-O theory, the spectra were characterized and the evaluated Ωλ parameters are found to be in the order: Ω2 > Ω4 > Ω6. The PL spectra recorded at λexc= 378 nm exhibited the emission bands due to 2H11/2→4I15/2 (B), S3/2→4I15/2(G), 4F9/2→4I15/2(O) and 4I13/2→4I15/2 (NIR) transitionsof Er3+ ions. With the gradual increase SeO2 content, the PL emission bands (especially green and NIR bands) have exhibited significant growth. The spectra were quantitatively analysed using kinetic rate equations and the causes for enhancement of PL emission were recognised and discussed. From the gain co-efficient G(λ) of the 4I13/2→4I15/2 transition, its lasing behaviour is detected for a population inversion of nearly 50%.

Dielectric and optical studies of CdSe nanoparticles: green synthesis

Nanoparticle of cadmium selenide (CdSe) was carried out through the green synthesis route method with the help of sodium selenite and cadmium nitrate. To control the size of nanoparticles, the capping agent utilized was starch. X-ray diffraction technique and transmission electron microscopy were used to calculate the grain size as well as the crystal structure of the particles was determined. The optical absorption spectra were studied by the UV–Visible spectroscopy. The morphology of prepared CdSe nanoparticles was studied by scanning electron microscope and TEM. The Fourier infrared spectroscopy (FTIR) was also carried out showing some dominant absorption peaks attributed to the characteristic absorption. The PL excitation spectra showed a single peak at 458 nm and broad PL emission band is visible at 677 nm in the emission spectra. Dielectric studies were carried out for the pelletized sample of CdSe nanoparticles in which the variation of the dielectric constant and dielectric loss were studied. This was done over the lower frequency range to higher frequency range at room temperature and other higher temperatures. The synthesized CdSe showed high dielectric constants at low frequency which rapidly decreases with the increase in the frequency. The dielectric loss also showed similar behavior with small difference. The semiconducting property of CdSe was confirmed, as with the increase of temperature the ac conductivity was also found to be increased.

Down and upconversion photoluminescence of ZrO2:Er3+ phosphor irradiated with 120 MeV gold ions

Down conversion and upconversion photoluminescence of pristine and gold ion irradiated ZrO2:Er3+ phosphor synthesized by solution combustion are reported. The crystallinity of the sample as analysed by x-ray diffraction shows a monoclinic phase having a crystallite size of about 57 nm calculated using Williamson—Hall formula. Field emission scanning electron microscopy shows that the shape and size of phosphor grains are non uniform. The down conversion photoluminescence of ZrO2:Er3+ has sharp emission bands in the red, green and blue regions of the spectrum. These emissions are corresponding to f–f transitions of Er3+ ions under excitation of 379 nm. In particular, the emission has maxima at 467, 492, 526, 548 and 660 nm correspond to 4F3/2 → 4I15/2, 4F7/2 → 4I15/2, 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions respectively. Interestingly, the PL emission intensity (excitation at 379 nm) is enhanced 1.6 times higher than pristine sample after 120 MeV Au ion irradiation for a fluence of 1 × 1010 ions cm−2. The blue to green emission ratio increases with the increase in ion fluence. Therefore, emission of the color shift towards bluish-white color with ion fluence. The lifetime of 4S3/2 level is found to be 16.9 and 71.5 μs for pristine and Au ion irradiated (1 × 1012 ions cm−2) ZrO2:Er3+ respectively. In near infrared (NIR) region, the PL emission band is observed at 1531 nm corresponding to 4I13/2 → 4I15/2 transition of Er3+ under excitation of 980 nm. The sample emits intense green emission and relatively weak red emission in up conversion PL under excitation of 980 nm. The ratio of intensities of red and green emission changes after Au ion irradiation is attributed to the corresponding change in the lattice symmetry in the host. Resulting in strong up conversion emission from two photon absorption process.

Dysprosium activated strontium aluminate phosphor: A potential candidate for WLED applications

A series of dysprosium activated strontium aluminate phosphors (SrAl2O4:xDy3+: x = 0.1, 0.2, 0.3, 0.4 and 0.5%) are prepared by conventional solid state reaction method. The structure of the prepared phosphors is analyzed by XRD. Results confirm that the crystal structure of the synthesized phosphors is monoclinic with space group P21. Morphology and microstructure of the synthesized phosphors is analyzed using FESEM and TEM analysis respectively. Optical properties are analyzed by using Raman and PL spectra. The characteristic peak observed at 465 cm−1 corresponds to bending mode of O–Al–O bonds in corners sharing with [AlO4]5- tetrahedral. The strongest PL emission band observed at 470 nm can be assigned to 4F9/2 - 6H15/2 transition in blue region when subjected to the ultraviolet excitation of wavelength 347 nm. White light is emitted by combination of red, yellow and blue emissions and is confirmed by CIE chromatic coordinate graph and the probable mechanism responsible for emission of the white light is explained in detail.

Structural, optical and terahertz properties of graphene-mesoporous silicon nanocomposites.

We investigate the structural, optical and terahertz properties of graphene-mesoporous silicon nanocomposites using Raman, terahertz time-domain and photoluminescence spectroscopy. The nanocomposites consist of a free-standing mesoporous silicon membrane with its external and pore surfaces coated with few-layer graphene. Results show a stabilization of the porous silicon morphology by the graphene coating. The terahertz refractive index and absorption coefficient were found to increase with graphene deposition temperature. Four bands in the 1.79–2.2 eV range emerge from the PL spectra of the nanocomposites. The broad bands centered at 1.79 eV and 1.96 eV were demonstrated to originate from Si nanocrystallites of different sizes. The narrower bands at 2.11 eV and 2.14 eV could be related to a thin SiC film at the Si/C interface.