The laser alloying technique is proposed and demonstrated to synthesize titanium silver nitride-based (Ti-Ag-N, TiN/TiAg) composite coating on Ag electroplated Cp-Ti and Ti6Al4V substrates under nitrogen shielding. The laser alloying was carried out using a continuous wave mode fiber coupled diode laser at 980 nm laser wavelength. Nitrogen shielding was useful to avoid interference from atmospheric oxygen and induce the formation of titanium nitride (TiN) phases. The formation of the TiN/TiAg composite was confirmed through surface morphology studies. The microstructural features and microhardness values (around 1000 HV0.2) confirmed the formation of composite Ti-Ag-N phases in the titanium alloy surface. In Ti6Al4V substrate laser alloyed with Ag and N, the formation of dendrites and columnar growth of the composite phases were observed. Ag was homogeneously distributed in the Ti/Ni matrix, and as the Ag coating thickness increased, the average microhardness of the laser alloyed coating decreased slightly.

Upconversion nanoparticles (UCNPs) are a fascinating group of luminescent materials known for their ability to convert low-energy photons to high-energy photons. Many inorganic UCNPs have been studied to understand the underlying mechanism of upconversion phenomena, out of which alkali rare-earth fluorides (AREFs) such as NaREF4, LiREF4 and KREF4 were found to exhibit high upconversion efficiencies. This work investigates a similar AREF upconversion nanoparticle viz RbY2F7:Yb, Er. This UCNP system was synthesised by a modified thermal decomposition method by varying the Yb concentration from 20% to 98%. Structural analysis using XRD revealed that all the synthesised samples were found to be formed in the orthorhombic phase irrespective of the increasing Yb concentration. The thermal decomposition method greatly aided in the reduction of particle size. HRTEM analysis revealed that the as-synthesised UCNPs have a spherical morphology with an average particle size of 7.9 ± 0.2 nm. The upconversion emission studies taken by exciting the samples with a 975 nm laser show three distinct peaks at 527, 542 and 656 nm. The experimental results indicate that the increased Yb3+ concentration improves the red to green intensity ratio by supporting the 4F9/2 → 4I15/2 transition of Er3+ through the energy back transfer process between Er3+ and Yb3+. Notably, there is a reduction in the overall emission intensity with increasing Yb3+ concentration. Furthermore, the decay lifetime studies show a decreasing trend at 542 nm and 656 nm emission lines with an increase in the Yb concentration, which is because of the concentration quenching effect of the increasing Yb concentration.

Present work deals with fabrication of superhard titanium boride coating on titanium surface with preplaced amorphous boron layer using high power diode laser alloying. Amorphous boron instantaneously converts into crystalline boron by the effect of high-power laser interaction, which rapidly drives the boron species into titanium liquid pool and form titanium boride precipitates by its convective flow. Negative Gibbs free energy (Delta G) and enthalpy (Delta H) of amorphous boron crystallization reaction introduces the concept of laser induced self-propagation synthesis. Gibbs free energy (Delta G) for the chemical reactions between Ti and B was calculated to confirm the spontaneous formation of titanium boride compound phases. The diffusion coefficient and activation energy were estimated to understand the phase formation and microstructural evolution. The structural phase, microstructure, microhardness and wear resistance of the laser borided titanium was investigated by XRD, optical and scanning electron microscopy, EDAX, Vickers microhardness analysis and linear reciprocating wear testing. The laser alloyed coating across the cross section shows formation of dendrites and whisker like microstructures. Average microhardness of 800-1600 HV0.2 was measured at different cross-sectional depths and an extreme hardness of about 3800-4700 HV0.2 was obtained in some regions of boron precipitates. The results showed a high negative value of Gibbs free energy of about -250 kJ/mol and -170 kJ/mol at similar to 2000 degrees C respectively which confirms the spontaneity of TiB2 and TiB phase formation. The activation energy of the titanium boride is estimated to be 140 kJ/mol. The laser borided coating with the formation of TiB and TiB2 phases could be useful for surface engineering applications.

This paper presents the upconversion emission and magnetic properties of NaGdF4:Yb, Er nanoparticles separately doped with Fe and Mg in the 10-40% concentration. The XRD analysis validates the structural properties of NaGdF4:Yb, Er nanoparticles with different concentrations of the dopants. The XPS spectra of Fe-doped NaGdF4:Yb, Er and Mg-doped NaGdF4:Yb, Er nanoparticles reveal the presence of the dopants and their valency. The 30%Mg doping resulted in an intense red upconversion emission at 650 nm compared to the Fe-doped NaGdF4:Yb, Er due to the high lifetime of 254 mu s for the F-4(9/2) -> I-4(15/2) (660 nm) energy level transitions of Er3+ ion. The Mg-doped nanoparticles showed a 2.7 red-to-green emission intensity ratio, 5.7 for Fe doping at the same 30% concentration and above this doping level, upconversion emission quenching resulted. The room temperature VSM study demonstrated paramagnetic property in the Mg-doped NaGdF4:Yb, Er nanoparticles characterized by negligible coercivity and retentivity with low saturation magnetization. Similar behaviour is also observed for the Fe-doped nanoparticles up to 20% concentration, and it became weak ferromagnetic at a high 30 and 40% dopant. In addition, the present work demonstrated the optical trapping of individual magnetic nanoparticles of 30%Fe-doped NaGdF4:Yb, Er by using a single beam optical tweezer technique under the tightly focused 980 nm diode laser interaction and the estimated trap stiffnesses is 1.85 pN mu m(-1) W-1. The multifunctional upconversion red emission, magnetic and optical trapping properties obtained in NaGdF4:Yb,Er,30%Fe nanoparticles can be used as a single particle probe in the theragnostic application.

Laser alloying creates a new alloy or ceramic composite coating with improved surface properties of materials. This work has developed a hard coating by high power diode laser alloying of preplaced TiB2 and amorphous boron (a-B) layer with Cp-Ti and Ti6Al4V substrates under argon and nitrogen gas shielding, which respectively termed as laser boriding and boronitride techniques. The composite coating was investigated by X-ray diffraction, Energy Dispersive X-ray, Elemental mapping, Optical microscopy and FESEM and Vickers hardness analyses. A simple analytical equation was employed to estimate surface temperature to correlate phase formation behavior. The XRD revealed the formation of TiB2 and TiB phases in the borided surface and TiB2, TiB, Ti4N3B2 phases in the laser boro-nitrided surface. The EDAX and elemental mapping confirmed the boron and nitrogen in the laser boro-nitrided cross section. The optical and scanning electron microscopy revealed that coating predominantly consists of TiB ceramic precipitates. A high hardness in the range 1217-3351 HV0.2 was obtained in the laser borided and boro-nitrided coating cross sections, due to the formation of TiB2 and Ti-B-N phases.

The effect of novel silver nanowire encapsulated NaGdF4:Yb,Er hybrid nanocomposite on the upconversion emission and bioimaging properties has been investigated. The upconvension nanomaterials were synthesised by polyol method in the presence of ethylene glycol, PVP and ethylenediamine. The NaGdF4:Yb,Er-Ag hybrid was formed with upconverting NaGdF4:Yb,Er nanoparticles of size ~ 80 nm and silver nanowires of thickness ~ 30 nm. The surface plasmon induced by the silver ion in the NaGdF4:Yb,Er-Ag nanocomposite resulted an intense upconversion green emission at 520 nm and red emission at 660 nm by NIR diode laser excitation at 980 nm wavelength. The UV-Vis-NIR spectral absorption at 440 nm and 980 nm, the intense Raman vibrational modes and the strong upconversion emission results altogether confirm the localised surface plasmon resonance effect of silver ion in the hybrid nanocomposite. MRI study of both NaGdF4:Yb,Er nanoparticle and NaGdF4:Yb,Er-Ag nanocomposite revealed the T1 relaxivities of 22.13 and 10.39 mM−1 s−1, which are larger than the commercial Gd-DOTA contrast agent of 3.08 mM−1 s−1. CT imaging NaGdF4:Yb,Er-Ag and NaGdF4:Yb,Er respectively showed the values of 53.29 HU L/g and 39.51 HU L/g, which are higher than 25.78 HU L/g of the CT contrast agent Iobitridol. The NaGdF4:Yb,Er and NaGdF4:Yb,Er-Ag respectively demonstrated a negative zeta potential of 54 mV and 55 mV, that could be useful for biological application. The in vitro cytotoxicity of the NaGdF4:Yb,Er tested in HeLa and MCF-7 cancer cell line by MTT assay demonstrated a cell viability of 90 and 80 %, respectively. But, the cell viability of NaGdF4:Yb,Er-Ag slightly decreased to 80 and 78%. The confocal microscopy imaging showed that the UCNPs are effectively up-taken inside the nucleolus of the cancer cells, and it might be useful for NIR laser–assisted phototherapy for cancer treatment.

Present work investigates about hydrothermally prepared LiYF4:Yb,Er nanocrystals with novel tunable emission and optical trapping results. Optical trapping effect of LiYF4:Yb,Er upconversion nanocrystal under 980 nm diode laser interaction is reported and a single nanoparticle trapping is demonstrated. Optical trapping force of 10.8 fN is exerted on LiYF4:Yb,Er upconversion nanocrystal of size similar to 238 nm at laser power 50 mW and the result is in agreement with the reported values. At 980 nm excitation, tunable green to red upconversion emission is achieved by calcination. It depends on orthorhombic and tetragonal phases that confirmed by XRD. The nanocrystals calcined at 450 and 600 degrees C resulted in a decay time of 26 and 19 mu s respectively and the upconversion emission mechanism is explained. FESEM and HRTEM examinations showed the hydrothermally synthesized nanocrystals are in trapezohedral, pyramidal, bi-pyramidal and tetragonal morphologies. The differential scanning calorimetry revealed the tetragonal phase formation temperature is lower at 450 degrees C compared to the reported value of 750 degrees C. The UV-VIS-NIR spectra of LiYF4:Yb,Er showed high absorption at 380, 480, 520 and 660 nm due to EP3+ ion and the broad absorption from 900 to 1000 nm centered at 980 nm is owing to Yb3+ ion. The crystalline phase, morphology, upconversion emission and optical trapping behaviors of LiYF4:Yb,Er nanocrystal are explained elaborately.

A novel “water-in-oil” type reverse microemulsion assisted synthesis detail on the formation of mixed cubic and hexagonal (α + β) phase NaYF4:Yb,Er nanoparticles and their upconversion emission properties are presented. The effect of surfactants, fluorine precursors on the crystallographic phase fraction, crystallite size of NaYF4:Yb,Er nanoparticles on red upconversion emission is discussed. The NaYF4:Yb,Er nanoparticles synthesized with CTAB, and oleic acid surfactants give larger crystallite size and moderate hexagonal/cubic phase fraction. It has resulted very intense upconversion red emission. The oleic-acid-free preparation of NaYF4:Yb,Er nanoparticles resulted highly-agglomerated nanoparticles and low crystallite size, which gives less-intense upconversion emission. The cubic and hexagonal phase fractions of NaYF4:Yb,Er depends on surfactants, microemulsion, molar concentrations of precursors, and post-calcination. All these factors influence the mondispersibility and upconversion red emission properties. The 980 nm laser pump power dependent upconversion emission studies have confirmed the typical two-photon behavior in α + β phase NaYF4:Yb,Er nanoparticles. Their decay life was also measured to correlate the upconversion red emission intensity. The effect of mixed α + β phase NaYF4:Yb,Er nanoparticles on the 1530 nm NIR emission is also presented.

This work presents a detailed microstructure-property correlation of high power diode laser nitrided titanium based on its dendrite and martensite microstructures, structural phase and microhardness. For the laser nitrided titanium, cooling rate was estimated for the first time using empirical power law relationship by considering the martensite width and dendrite arm spacings and the results were validated by analytical thermal model. A processing window was formulated for laser gas nitriding of titanium by relating the experimental parameters such as laser processing parameters, nitrogen gas pressure and titanium nitride phases. The novelty of this work is demonstration of laser nitriding of titanium in laminar flow nitrogen gas environment using a simple acrylic container setup that avoids design and fabrication of a complex gas nozzle delivery system. In this setup, a thin transparent acrylic sheet was used as optical window instead of expensive quartz glass, to transmit high power diode laser beam at 980 nm wavelength to irradiate the substrate work piece in a closed container. This simple laser nitriding technique has created characteristic golden colored TiN surface with high surface hardness. Dendrite and martensite microstructures of the laser nitrided titanium were analyzed by optical and FESEM microscopy. EDAX analysis revealed the presence of nitrogen in laser nitrided titanium and X-ray diffraction confirmed the TiN phases. The microhardness of laser nitrided titanium is six times higher than its substrate.

The present report explores third order nonlinear optical behavior of phase pure Yb3+:YAG nanoparticles for the first time by Z-scan technique. The measurement was carried out using diode pumped continuous wave (CW) Nd:YAG laser at 532 nm. The Yb:YAG nanoparticles exhibit characteristic near-infrared (NIR) emission at 1030 nm under 940 nm excitation. The nanoparticles exhibit high nonlinear refractive index (n(2) = 8.649 x 10(-8) cm(2)/W) and low nonlinear absorption coefficient (beta= 0.109 x 10(-4 )cm/W) giving an appreciable figure of merit (FOM) of similar to 74.50. The excitation power (8.2-10.5W cm(-2 )) dependent emission spectra were recorded to study exchange energy interaction of Yb3+ ions with YAG host lattice. By utilizing the nonlinear refractive index 'n(2)' from Z-scan measurement, thermo-optic coefficient (dn/dt) was calculated to demonstrate Yb3+ :YAG nanomaterial for high power compact solid state laser gain amplifier systems.

Surface encapsulation of nanophosphors by nanoscale silica (SiO2) coating is an effective strategy to enhance the luminescence property for opto-electronic application. The present work investigates about the synthesis of silica encapsulated LuAG:Pr3+ nanocrystals by surfactant assisted co-precipitation and rapid microwave calcination. The ultrafast microwave heating of silica encapsulated LuAG:Pr at 1050 degrees C for 10 min resulted in the formation of well-crystallized nanocrystals in cubic phase that evidenced by XRD Rietveld analysis. FE-SEM and HR-TEM examinations revealed the formation of similar to 6 nm nanoscale silica film encapsulation on LuAG:Pr nanocrystals. EDS elemental and XPS investigations confirmed the presence of SiO2 layer encapsulation on the surface of nanoparticle. The nanoscale silica encapsulated LuAG:Pr nanocrystals displayed two-fold enhancement in luminescence red emission than uncoated counterpart nanocrystals. The continuous nanoscale silica coating served as an integrating sphere that confides incident photons by means of multiple reflections and improved the light extraction. Temperature dependent photoluminescence analysis of the silica coated LuAG:Pr3+ nanocrystal was also studied. It revealed the original emission intensity was stable up to 425 K and start decreasing to 55% at 520 K, which promoted stable high temperature luminescence behavior. Thermoluminescence investigation was also performed for uncoated and silica-coated LuAG:Pr nanocrystals by irradiated them with high energy gamma-ray (Co-60) source at 200 Gy for 2 min. The trap-depth in terms of activation energy (E) and frequency factor (s) of the gamma ray irradiated nanoparticles was estimated by computerized GCD operation.

In this report graphene oxide is successfully prepared by modified Hummers’ method at room temperature without using low temperature ice bath reactor. For the fabrication of DSSC photoanode, rGO-TiO2 nanocomposite was prepared using a novel two step hydrothermal and solar exfoliation process. Formation of anatase TiO2 with tetragonal structure is confirmed using XRD pattern. Peak splitting occurs in Raman 2D band indicates the presence of bi-layer rGO. FESEM and HRTEM studies show the synthesized spherical shaped TiO2 nanoparticles embedded on rGO flakes and the average particulate size is found to be c.a 10 nm. FTIR and XPS results confirm the formation of direct bonding between Ti and C atoms in rGO-TiO2 by the observation of vibrational band at 1124 cm−1 and binding energy at 284.13 eV respectively. DSSC devices are fabricated and EIS measurements are performed to determine interfacial charge transfer kinetics such as chemical capacitance, recombination resistance and electron lifetime. Here, we report for the first time the results on the co-sensitization of solar exfoliated rGO-TiO2 as photoanode using a combination of metal-free and metal-based organic dyes. Enhanced PCE of 6.9% is realized in N719 + N3 co-sensitized DSSC by its increased electron recombination lifetime.

SrF2 based upconversion nanoparticles (UCNPs) were synthesized by hydrothermal method using ethylenediaminetetraacetic acid (EDTA) as surfactant, by doping with single-lanthanide-activator Er ion and sensitizer-activator Yb3+−Er3+ ion-pair. The excited state absorption (ESA) and energy transfer upconversion (ETU) properties were investigated respectively by synthesizing SrF2:2%Er and SrF2:20%Yb,2%Er nanoparticles. EDTA aided hydrothermal synthesis resulted in nano-rod, nano-plate and nano-sphere morphological particles. The hydrothermally grown SrF2:Yb,Er UCNPs are formed as nano-spheres in size ~ 30 to 60 nm. It gives a high specific surface area of 47.17 to 23.58 m2 g−1. The nano-spherical SrF2:Yb,Er resulted an intense red upconversion emission at 660 nm, under the near-infrared (NIR) 980 nm excitation, due to its high specific surface area and ETU mechanism. The post-calcined SrF2:Yb3+,Er3+ gives better red-to-green emission intensity ratio compared to the as-prepared counterparts. SrF2:Er3+ gives very weak red emission due to ESA mechanism. The optical energy gap of SrF2:Yb,Er UCNP was calculated using the barycentre of green emission at 524 and 542 nm from the thermally coupled energy levels of 2H11/2 and 4S3/2. It gives an optical energy gap of 766 cm−1 and the estimated thermal sensitivity is 1.22% K−1 at 300 K. The result is in agreement with other published reports. We also demonstrated the NIR-to-NIR (980-to-850 nm) upconversion emission in the SrF2:Yb3+, Er3+ nanoparticle.

Micro/Nanoscale binary (CoS, NiS, and ZnS) and ternary (CoNi2S4 and Zn0.76Co0.24S) metal sulfides were directly grown on FTO substrates by a novel one step hydrothermal method for low-cost DSSC counter electrode applications. XRD study confirms phase pure formation of CoS, NiS, ZnS, CoNi2S4 and Zn0.76Co0.24S. HRSEM images of CoS, NiS and CoNi2S4 films exhibits hierarchical flower, hexagonal microcage and flake like particulates respectively. The ZnS and Zn0.76Co0.24S films show spherical micro-nanoparticles. The nanoflake morphological CoS and CoNi2S4 revealed high surface area measured by BET analysis. XPS result confirms the chemical states of CoNi2S4 and Zn0.76Co0.24S. A detailed electrochemical cyclic voltammetry, Tafel polarization and electrochemical impedance spectroscopy (EIS) analyses reveals the ternary metal sulfide (CoNi2S4) possesses an excellent electrocatalytic activity and electrical conductivity than other counter electrodes for the reduction of tri-iodide to iodide. Photovoltaic performance of the devices was studied using standard solar simulator at 1 Sun intensity (AM 1.5 G) and dark conditions. The reduced dark current obtained in CoNi2S4 and Zn0.76Co0.24S confirms the less recombination of electrons in ternary metal sulfides based DSSCs. The power conversion efficiency of similar to 4.03% achieved in Pt-free CoNi2S4 counter electrode is comparable to standard Pt based DSSC (similar to 4.59%). The CoNi2S4 exhibiting good device performance and high electrocatalytic activity can serve as efficient low-cost counter electrode for Pt-free DSSCs.

In this work, NaxScF3+x:Yb,Er upconversion nanoparticles (UCNPs) were synthesized by co-precipitation method. The pH dependent effect on phase formation of the UCNPs and its upconversion emission is investigated. XRD analysis confirmed NaScF4:Yb,Er nanoparticles are crystallized in mixed phases of monoclinic and hexagonal structure. The nanoparticles are formed in 80-120 nm size with spherical, rectangular and thin flake morphologies that depend upon neutral and alkali precipitation conditions. Under the 980nm diode laser excitation, the hexagonal NaScF4:Yb,Er nanoflake shaped nanoparticles yielded intense red upconversion emission. A four-fold improvement in red upconversion is obtained in lower symmetric hexagonal NaScF4:Yb,Er than high symmetric cubic NaScF4:Yb,Er nanoparticles. The intense red emitting NaScF4:Yb, Er is preferable than green emitting NaYF4:Yb,Er UCNPs for bioimaging applications.

Co-sensitization of metal-free (Eosin and Coumarin) and metal-based (N3 and N719) organic dye combinations were employed with TiO2 nanoparticles based photoanodes for the fabrication of dye-sensitized solar cells. The charge injection and oxidized dye regeneration process in mono and co-sensitized system were explored from the constructed energy level diagram using cyclic voltammetry analysis. Electrochemical impedance measurements were performed to determine interfacial charge transfer kinetics such as chemical capacitance, recombination resistance and electron lifetime. Current density–Voltage (J–V) characteristics resulted an improved efficiencies in co-sensitized DSSCs due to increased short circuit current density (Jsc). The studies on polarization effect was also evaluated using conductivity plot of impedance spectroscopy. Here, we report for the first time, the internal polarization of dye-sensitizers contributes a small current in the total obtained current density (Jsc) of a device besides the conduction current which enhances the PCE. Especially, high polarization effect of coumarin dye by its resonance polar structure increasing the conductivity in intermediate frequency region of conductivity plot and thus the current density gets enhanced. Improved efficiency of ~ 5.4% was realized in pure metal-based dye co-sensitization by its optimized electron concentration in CB TiO2 to balance charge injection and recombination.

This work presents the first time synthesis of photon upconverting cubic BaYF5:Yb-3, Er3+ nanoclusters by a novel reverse microemulsion method. Rietveld refinement analysis confirmed the cubic BaYF5 and BaYF5:Yb, Er. The spherical nanoclusters (similar to 35 nm) are formed by an ensemble of similar to 10 nm individual nanocrystals. A plausible formation mechanism is explained based on HRSEM and HRTEM investigations. FTIR revealed the effect of CTAB and oleic acid surfactants on amine and carboxyl functionalization. The cubic BaYF5:Yb,Er nanoclusters exhibited an intense green upconversion emission under 980 nm excitation. A three-fold upconversion green emission enhancement was achieved by increasing the calcination temperature from 200 degrees C to 400 degrees C. The energy transfer mechanism is described based on pump power dependent upconversion luminescence intensity. Furthermore, cytotoxicity effect of the different concentrations (2.5-300 mu g/mL) of the BaYF5:Yb, Er were investigated against human colon adenocarcinoma cell line (HT29 cells) for 24 h and 48 h treatment.

A novel synthesis approach is proposed to prepare strong NIR emitting Yb3+ doped YAG (Yb:YAG) nanoparticles at different Yb3+ concentrations by a modified refluxer assisted homogeneous precipitation using dual polymeric surfactant functionalization approach. Ultrafast microwave calcination has achieved Yb:YAG nanoparticles in pseudo-spherical morphology under the influence of polymeric dual SDS-PEG surfactants, evidenced from HR-TEM observation. XRD pattern of Yb:YA(G) nanoparticles calcined at 900 degrees C resulted in cubic phase formation without the evolution of YAlO3 and Y3AlO4 intermediate phases. XPS analysis revealed the presence of Yb3+ and Yb2+ mixed valence states in high-Yb doped YAG, whereas only Yb3+ is seen in moderately-Yb doped YAG nanoparticles. UV-Visible diffuse reflectance spectrum exhibit characteristic optical absorption at 940 nm is attributed to F-2(7/2) -> F-2(5/2) electronic transitions of Yb3+ ions. From these spectral data, optical parameters such as Stark energy splitting (Delta E), absorption coefficient (alpha), refractive index (n) and absorption cross section (sigma(abs)) are estimated. Photoluminescence spectra of moderately (5 at%) doped Yb:YAG nanoparticles showed strong near infrared emission at 1030 nm due to Yb3+ ions that confirmed by XPS analysis. Also, the stimulated emission cross section (sigma(em)) is calculated using Fuchtbauer-Ladenburg equation. The fluorescence decay lifetime result also implies that the moderately doped YY-5S sample exhibits higher decay lifetime of 2.08 ms. In addition, present work explores the thermally stimulated luminescence properties of Yb:YAG nanoparticles for the first time by high energy gamma-ray irradiation at different dose rates. TSL kinetic parameters such as structural factor (mu(g)), order of kinetics (b), trap depth in terms of activation energy (E) and frequency factor (s) are estimated.

•Femtosecond laser surface texturing of Tin Bronze alloy reported first time.•Effect of scanning speed and tin content on groove geometry.•Reciprocating wear behavior of tin bronze alloy.