A. K. Parchur

Behaviour of electric and magnetic dipole transitions of Eu3+, 5D0 → 7F0 and Eu–O charge transfer band in Li+ co-doped YPO4:Eu3+

The effect of Li+ co-doping on the photoluminescence properties of YPO4:Eu is discussed. Interesting behaviours, such as the presence of intermediate bands, shifting of the Eu–O charge transfer band (Eu–O CTB) to a lower wavelength, variation in intensities of magnetic (5D0 → 7F1) and electric dipole (5D0 → 7F2) transitions of Eu3+ and shift of 5D0 → 7F0 to higher energy with increasing excitation wavelengths are observed. The Eu3+ ion does not have an absorption band in the range 340–350 nm, but after excitation at these wavelengths, a broad emission band (370–570 nm), as well as sharp peaks of Eu3+, could be observed. This is due to strong energy transfer from the intermediate band of the host to the Eu3+ ion. X-ray photoelectron spectroscopy (XPS) study also confirms that intermediate band emission is not due to Eu2+ ion emission. The blue shifting of Eu–O CTB is because of the increase in the optical electronegativity of the Eu3+ ion on Li+ co-doping. The variation in intensities of the 5D0 → 7F2 and 5D0 → 7F1 dipole transitions is related to (i) overlapping interaction parameters within the ground and excited states, (ii) exchange interaction among atoms/ions and (iii) density of the incoming photons. Shift of 5D0 → 7F0 to a higher energy with increasing excitation wavelengths is because of change in the second order crystal field parameter B20 with excitation wavelength. The significant enhancement of luminescence intensity is found with Li+ co-doping due to the increase in crystallinity.

Observation of intermediate bands in Eu3+ doped YPO4 host: Li+ ion effect and blue to pink light emitter

This article explores the tuning of blue to pink colour generation from Li+ ion co-doped YPO4:5Eu nanoparticles prepared by polyol method at ∼100-120 °C with ethylene glycol (EG) as a capping agent. Interaction of EG molecules capped on the surface of the nanoparticles and/or created oxygen vacancies induces formation of intermediate/mid gap bands in the host structure, which is supported by UV-Visible absorption data. Strong blue and pink colors can be observed in the cases of as-prepared and 500 °C annealed samples, respectively. Co-doping of Li+ enhances the emission intensities of intermediate band as well as Eu3+. On annealing as-prepared sample to 500 °C, the intermediate band emission intensity decreases, whereas Eu3+ emission intensity increases suggesting increase of extent of energy transfer from the intermediate band to Eu3+ on annealing. Emission intensity ratio of electric to magnetic dipole transitions of Eu3+ can be varied by changing excitation wavelength. The X-ray photoelectron spectrosc...

In-vitro cyto-toxicity, geno-toxicity, and bio-imaging evaluation of one-pot synthesized luminescent functionalized mesoporous SiO2@Eu(OH)(3) core-shell microspheres

UNLABELLED Luminescent functionalized mesoporous SiO2@Eu(OH)3 core-shell microspheres (LFMCSMs) were prepared by coating of europium hydroxide (Eu(OH)3) shell on mesoporous silica (SiO2) nanospheres via a facile one-pot process at low temperature. The FETEM images revealed that a well-defined luminescent europium hydroxide shell was successfully grafted on the surface of mesoporous silica nanospheres. These experimental results showed that the LFMCSM has a typical diameter of ca. 392 nm consisting of the silica core with about 230 nm in diameter and europium hydroxide shell with an average thickness of about 162 nm. LFMCSMs exhibited strong red emission peak upon irradiation with ultraviolet light, which originated from the electric-dipole transition (5)D0 → (7)F2 (614 nm) of Eu(3+) ion. The biocompatibility of the synthesized LFMCSMs was evaluated in vitro by assessing their cytotoxic and genotoxic effect on human hepatoblastoma (HepG2) cells using MTT, TUNEL, fluorescent staining, DNA ladder and Gene expression assays respectively. FROM THE CLINICAL EDITOR This paper describes the development of a one-pot synthesis of luminescent mesoporous SiO2@Eu(OH)3 core-shell microspheres and evaluates their favorable in vitro cyto-toxicity and geno-toxicity, and their applications in bio-imaging of these particles that emit bright red signal under UV exposure.

Preparation, microstructure and crystal structure studies of Li+ co-doped YPO4:Eu3+

Rod-like shape particles of tetragonal phase Li+ co-doped YPO4:Eu samples are prepared by using a polyol method at low temperature (∼100–120 °C for 1 h). Li+ co-doping enhances the crystalline nature of the sample and reduces the agglomeration among the particles. The shift in the reflection peaks of the tetragonal phase to the lower 2θ angle in the X-ray diffraction pattern indicates the occupancy of Li+ ions in the interstitial sites of the host lattice. The point group symmetry of Y3+/Eu3+ in YPO4 is demonstrated in simple representation.

Effect of surface coating on optical properties of Eu3+-doped CaMoO4 nanoparticles

A simple polyol method has been used for the synthesis of CaMoO4:Eu (core), CaMoO4:Eu@CaMoO4 (core/shell) and their silica coated CaMoO4:Eu@CaMoO4 (core/shell/shell) nanoparticles. X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), Fourier transform Raman (FT-Raman), Fourier transform infrared (FT-IR), UV/Vis absorption and photoluminescence (PL) spectroscopies techniques has been employed for their characterization. XRD patterns and FT-Raman spectra showed that these nanoparticles have a scheelite-type tetragonal structure without the presence of deleterious phases. These nanoparticles were easily dispersed in water, producing a transparent colloidal solution. The optical energy band-gap decreases after core/shell formation due to increase the crystalline size. The photoluminescence (PL) spectra of the as-synthesized core, core/shell and core/shell/shell nanoparticles measured with an excitation source wavelength of 325nm showed that the emission intensity was increases after shell formation around the surface of core nanoparticles.

Highly aqueous soluble CaF2:Ce/Tb nanocrystals: effect of surface functionalization on structural, optical band gap, and photoluminescence properties

The design of nanostructured materials with highly stable water-dispersion and luminescence efficiency is an important concern in nanotechnology and nanomedicine. In this paper, we described the synthesis and distinct surface modification on the morphological structure and optical (optical absorption, band gap energy, excitation, emission, decay time, etc.) properties of highly crystalline water-dispersible CaF2:Ce/Tb nanocrystals (core-nanocrystals). The epitaxial growth of inert CaF2 and silica shell, respectively, on their surface forming as CaF2:Ce/Tb@CaF2 (core/shell) and CaF2:Ce/Tb@CaF2@SiO2 (core/shell/SiO2) nanoarchitecture. X-ray diffraction and transmission electron microscope image shows that the nanocrystals were in irregular spherical phase, highly crystalline (~20 nm) with narrow size distribution. The core/shell nanocrystals confirm that the surface coating is responsible in the change of symmetrical nanostructure, which was determined from the band gap energy and luminescent properties. It was found that an inert inorganic shell formation effectively enhances the luminescence efficiency and silica shell makes the nanocrystals highly water-dispersible. In addition, Ce3+/Tb3+-co-doped CaF2 nanocrystals show efficient energy transfer from Ce3+ to Tb3+ ion and strong green luminescence of Tb3+ ion at 541 nm(5D4→7F5). Luminescence decay curves of core and core/shell nanocrystals were fitted using mono and biexponential equations, and R2 regression coefficient criteria were used to discriminate the goodness of the fitted model. The lifetime values for the core/shell nanocrystals are higher than core-nanocrystals. Considering the high stable water-dispersion and intensive luminescence emission in the visible region, these luminescent core/shell nanocrystals could be potential candidates for luminescent bio-imaging, optical bio-probe, displays, staining, and multianalyte optical sensing.Graphical AbstractA newly designed CaF2:Ce/Tb nanoparticles via metal complex decomposition rout shows high dispersibility in aqueous solvents with enhanced photoluminescence. The epitaxial growth of inert CaF2 shell and further amorphous silica, respectively, enhanced their optical and luminescence properties, which is highly usable for luminescent biolabeling, and optical bioprobe etc.

Synthesis and characterization of bifunctional hybrid nanocomposite YPO4:5Eu@Fe3O4

Spherical, non-agglomerated and highly water dispersed bifunctional YPO4:5Eu@Fe3O4 nanocomposite was prepared by coprecipitation method. The nanohybrid shows characteristic induction heating under AC magnetic field by reaching the hyperthermia temperature (∼42°C) and giving red emission under 395nm excitation, characteristic of Eu3+, thus potential material for biological applications.

Luminescence and electrical behavior of lead molybdate nanoparticles

We report our investigation on photoluminescence and electrical behavior of lead molybdate (PbMoO4) nanoparticles by spanning the solvent of reaction medium. The PbMoO4 nanoparticles were prepared in different solvents like ethylene glycol (EG), dimethyl sulfonic acid (DMSO) and 50% EG + 50% DMSO at room temperature. The crystallite size and strain acting on nanoparticles were characterized by X-ray diffraction (XRD) study and microstructure was studied by transmission electron microscope (TEM). The average crystallite sizes and strain were found to be ∼22, 24 and 25 nm and ∼0.0028, 0.0039 and 0.0048 for EG, DMSO and EG+DMSO solvents, respectively. The XRD peak corresponding to (112) were found to shift to lower angle by 0.02° for DMSA solvent as compared to EG. This confirmed the lattice expansion in the unit cell. The particle sizes measured from TEM measurements were found to be slightly greater than that obtained from XRD analysis. The photoluminescence (PL) measurements were carried out by using 266 ...

CaMoO[sub 4]:Tb@Fe[sub 3]O[sub 4] hybrid nanoparticles for luminescence and hyperthermia applications

We have prepared CaMoO4:Tb@Fe3O4 hybrid nanoparticles by co-precipitation and polyol method. Their temperature kinetics for hyperthermia temperature ∼43 °C under different applied AC fields and the luminescence properties under UV-radiation are investigated. A strong green emission is observed due to the presence of Tb3+ ions.