N. Yaiphaba

Luminescence, lifetime, and quantum yield studies of redispersible Eu3+-doped GdPO4 crystalline nanoneedles: Core-shell and concentration effects

Crystalline nanoneedles of Eu3+-doped GdPO4 and Eu3+-doped GdPO4 covered with GdPO4 shell (core shell) have been prepared at relatively low temperature of 150 °C in ethylene glycol medium. From luminescence study, asymmetric ratio of Eu3+ emission at 612 nm (electric dipole transition) to 592 nm (magnetic dipole transition) is found to be less than one. Maximum luminescence was observed from the nanoparticles with Eu3+ concentration of 5 at. %. For a fixed concentration of Eu3+ doping, there is an improvement in emission intensity for core-shell nanoparticles compared to that for core. This has been attributed to effective removal of surface inhomogeneities around Eu3+ ions present on the surface of core as well as the passivation of inevitable surface states, defects or capping ligand (ethylene glycol) of core nanoparticles by bonding to the shell. Lifetime for D50 level of Eu3+ was found to increase three times for core-shell nanoparticles compared to that for core confirming the more Eu3+ ions with sym...

Is Higher Ratio of Monoclinic to Tetragonal in LaVO4 a Better Luminescence Host? Redispersion and Polymer Film Formation

Crystalline LaVO4:Eu(3+) nanophosphors (NPs) codoped with metal ions (M(n+) = Li(+), Sr(2+), and Bi(3+)) are prepared in ethylene glycol (EG) medium at temperature ∼140 °C in 3 h. A mixture of monoclinic and tetragonal phases is observed. The ratio of tetragonal to monoclinic phases increases with increase of Li(+) and Sr(2+) concentration, but this is opposite in case of Bi(3+) concentration. Lattice expansion occurs in the case of Li(+) and Sr(2+) codoping. Li(+) ions occupy the interstitial sites instead of La(3+) sites. Lattice contraction occurs in case of Bi(3+) codoping indicating substitution of La(3+) sites. Luminescence intensity is improved by codoping of M(n+) irrespective of crystal structure. Charges of Li(+) and Sr(2+) are different from that of La(3+) (host lattice), whereas the charge of Bi(3+) is same as that of La(3+). One interesting observation is in magnetic dipole transition that the intensity of the peak at 594 nm is more than that at 587 nm in the case of charge imbalance, whereas the reverse occurs in the case of charge balance. LaVO4:Eu(3+) nanophosphors prepared in water medium have more luminescence intensity when compared to those prepared in ethylene glycol, and this is related to variation of ratio of tetragonal to monoclinic phases. The luminescence intensity is also enhanced as annealing temperature increases from 600 to 800 °C due to the improved crystallinity. Lifetime data are analyzed on the basis of exponential and nonexponential decay equations. Samples are dispersible in polar medium due to capping of particles by EG. Polymer films are prepared by dispersion of NPs in poly(vinyl alcohol), and extra borax is added in order to make cross-link between polymer molecules. Samples of NPs in the forms of powder, dispersion in liquid medium, and film show the red emission.

Calculation and Comparison of Energy Interaction and Intensity Parameters for the Interaction of Nd(III) with DL-Valine, DL-Alanine and -Alanine in Presence and Absence of / in Aqueous and Different Aquated Organic Solvents Using 4f-4f Transition Spectra as Probe

Absorption difference and comparative absorption spectrophotometric studies involving 4f-4f transitions of Nd(III) and different amino acids: DL-valine, DL-alanine, and -alanine in presence and absence of Ca(II) and Zn(II) in aqueous and different aquated organic solvents have been carried out. Variations in the spectral energy parameters: Slater-Condon () factor, Racah (), Lande factor (), nephelauxetic ratio (), bonding (), percentage covalency () are calculated to explore the mode of interaction of Nd(III) with different amino acids: DL-valine, DL-alanine, and -alanine. The values of experimentally calculated oscillator strength (P) and computed values of Judd-Ofelt electric dipole intensity parameters, ( = 2,4,6), are also determined for different 4f-4f transitions. The variation in the values of P and parameters explicitly shows the relative sensitivities of the 4f-4f transitions as well as the specific correlation between relative intensities, ligand structures, and nature of Nd(III)-ligand interaction.