Ravi Sharma

Chemical route synthesis dependent particle size of Mn activated ZnS nanophosphors

The synthesis and optical properties of Mn activated ZnS nanoparticles are reported in this paper. Nanoparticles of zinc sulphide were prepared by chemical route technique; whereas mercaptoethanol (ME) was used as the capping agent. The particle size of such nanocrystals was measured using XRD, SEM and TEM patterns and was found to be in between 3 nm to 5 nm. The blue-shift in the absorption spectra was found with reducing size of the nanoparticles. It was also found that the change in Mn concentrations does not influence the particle size and blue-shift in the absorption spectra. The optical absorption edge was found at 296 nm for all the doped samples for fixed concentration of capping agent. The particle size of nanoparticle was calculated both theoretically and experimentally, which is nearly the same. The FTIR spectra inferred that the stabilising agent passivates the surface of the particles.

Mechanoluminescence & Thermoluminescence of SrAl2O4: EUNano-Phosphors

Eu doped strontium Aluminate phosphors were synthesized by combustion method using urea as a reducer at initiating temperature of 600 o C. We have investigated the Fracto- Mechanoluminescence (ML) and Thermoluminescence (TL) of SrAl2O4: Eu. Two peaks have been found in time Vs ML intensity plot. The peak of ML intensity Vs time curve increases with increasing velocity of the piston. The total ML intensity (area below the curve) also increases with impact velocity and attains saturation at higher value of the impact velocity. We have also investigated that the ML intensity is completely recovered by irradiation with ultraviolet light. The TL intensity was recorded for different exposure time with UV light and it was observed that TL intensity is maximum for 15 minute exposure time. We have calculated the trap depth by different methods.

A study on the luminescence properties of gamma-ray-irradiated white light emitting Ca2Al2SiO7:Dy3+ phosphors fabricated using a combustion-assisted method

Ca2Al2SiO7:Dy3+ phosphors emitting long-lasting white light were synthesized by a combustion-assisted method. The phase structure, surface morphology, particle size, and elemental composition were analysed using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) techniques. The XRD profiles showed that all peaks could be attributed to the tetragonal Ca2Al2SiO7 phase when the sample was annealed at 1100 °C for 4 hours. The thermoluminescence (TL) intensity increased with increasing γ-dose and it seemed to become saturated at 1180 Gy. The increase in TL intensity indicates that the concentration of traps increased with the γ-dose. Moreover, the depths and frequency factors of the trap centers were calculated from the TL glow curve of the sample, which indicated that the trap centers corresponding to the 420 K (1st peak) and 462 K (2nd peak) band were more helpful to long-lasting phosphorescence. Under γ-excitation, the TL emission spectra of the Ca2Al2SiO7:Dy3+ phosphor showed the characteristic Dy3+ emission peaks at 484 nm (blue), 583 nm (yellow), and 680 nm (red), originating from the transitions 4F9/2 → 6H15/2, 4F9/2 → 6H13/2, and 4F9/2 → 6H11/2, respectively. Photoluminescence (PL) decay is also reported and it indicates that the Ca2Al2SiO7:Dy3+ phosphor shows fast and slow decay processes. The effect of the doping concentration on the crystal structure and the luminescence properties of the Ca2Al2SiO7:Dy3+ phosphors was investigated. The peak for the mechanoluminescence (ML) intensity increases linearly with the increasing impact velocity of the moving piston. The possible mechanisms of the TL, PL, and ML of the white light emitting long-lasting phosphor are also discussed.

Effect of capping agent on the particle size of CdSe nanoparticles

CdSe nanoparticles were synthesized by green route and chemical route methods. In the green route method the samples were capped by starch and in the chemical route method the samples were capped by mercaptoacetic acid (MAA). The samples were characterized by powder X- ray diffraction (XRD) and transmission electron microscopy (TEM). Both the samples showed zinc blend structure. The optical absorption spectra and Fourier transform infrared (FTIR) spectra were also studied. A blue shift was seen in the absorption spectra as compared with the bulk as well as the sample capped by starch. TEM images showed agglomeration for the starch-capped sample as compared with the MAA-capped sample. The particle size for the sample capped by MAA was found to be less as compared with the starch-capped sample. A blue shift in the photoluminescence (PL) spectra was also recorded for the samples prepared by the chemical route as compared with the sample prepared by the green route as well as the bulk. The PL peak shifted towards the red side and increase in the peak intensity occurred with the change in the excitation wavelength. Change in PL intensity was observed with different pH at 685 nm. Copyright

Ca2Al2SiO7:Ce3+ phosphors for mechanoluminescence dosimetry

A series of Ce3+ ion single-doped Ca2 Al2 SiO7 phosphors was synthesized by a combustion-assisted method at an initiating temperature of 600 °C. The samples were annealed at 1100 °C for 3 h and their X-ray diffraction patterns confirmed a tetragonal structure. The phase structure, particle size, surface morphology and elemental analysis were analyzed using X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy techniques. Thermoluminescence (TL) intensity increased with increase in ultraviolet (UV) light exposure time up to 15 min. With further increase in the UV irradiation time the TL intensity decreases. The increase in TL intensity indicates that trap concentration increased with UV exposure time. A broad peak at 121 °C suggested the existence of a trapping level. The peak of mechanoluminescence (ML) intensity versus time curve increased linearly with increasing impact velocity of the moving piston. Mechanoluminescence intensity increased with increase in UV irradiation time up to 15 min. Under UV-irradiation excitation, the TL and ML emission spectra of Ca2 Al2 SiO7 :Ce3+ phosphor showed the characteristic emission of Ce3+ peaking at 400 nm (UV-violet) and originating from the Ce3+ transitions of 5d-4f (2 F5/2 and 2 F7/2 ). The photoluminescence (PL) emission spectra for Ca2 Al2 SiO7 :Ce3+ were similar to the ML/TL emission spectra. The mechanism of ML excitation and the suitability of the Ca2 Al2 SiO7 :Ce3+ phosphor for radiation dosimetry are discussed. Copyright

Effect of capping agent concentration on thermoluminescence and photoluminescence of copper-doped zinc sulfide nanoparticles.

Copper-doped zinc sulfide (ZnS:Cu) nanoparticles with varying concentrations of capping agent were prepared using a chemical route technique. These particles were characterized by scanning electron microscopy (SEM), transmission electron microscopy and X-ray diffraction (XRD). Optical absorption studies showed that the absorption edge shifted towards the blue region as the concentration of the capping agent increased. Using effective mass approximation, calculation of the nanoparticle size indicated that effective band gap energy increases with decreasing particle size. The thermoluminescence (TL) properties of sodium hexameta phosphate (SHMP)-passivated ZnS:Cu nanoparticles were investigated after UV irradiation at room temperature. The TL glow curve of capped ZnS:Cu showed variations in TL peak position and intensity with the change in capping agent concentration. The photoluminescence (PL) spectra of ZnS:Cu nanoparticles excited at 254 nm exhibited a broad green emission band peaking around 510 nm, which confirmed the characteristic feature of Zn(2+) as well as Cu(2+) ions as the luminescent centres in the lattice. The PL spectra of ZnS:Cu nanoparticles with increasing capping agent concentrations revealed that the emission becomes more intense and shifted towards shorter wavelengths as the sizes of the samples were reduced.