• S J Dhoble

Articles written in Bulletin of Materials Science

• Preparation and characterization of Eu3+ activated CaSiO3, (CaA)SiO3 [A = Ba or Sr] phosphors

Eu3+ activated CaSiO3, (Ca, Ba) SiO3 and (Ca, Sr) SiO3 have been prepared by sol–gel technique. Residual solvent and organic contents in the gel were removed by firing at 100°C for 3–4 h at 300 and 600°C for 2 h. Small exothermic shoulder around 850 to 875°C, as observed in DTA curve, corresponds to crystallization temperature of the doped calcium silicate. Influence of firing temperature on the luminescence of Eu3+ shows the maximum emission intensity in gel fired at 850°C. Photoluminescence emission peak is observed at 614 nm due to ${}^{5}D_{0} \rightarrow {}^{7}F_{2}$ transition of Eu3+ ion in (Ca, Ba) SiO3 and (Ca, Sr) SiO3 phosphors, when excited by 254 nm. The (Ca, Ba) SiO3 material is proposed as an efficient red phosphor.

• Luminescent studies of impurity doped SrS phosphors

SrS phosphors activated with Ce and Dy ions were prepared by solid-state diffusion method. Photoluminescent study was carried out on SrS : Ce, SrS : Dy and SrS : Dy, Ce. Thermoluminescence and electron spin resonance studies were also carried out on SrS : Dy phosphor. The thermoluminescence glow curve shows a peak at around 142°C. Irradiated SrS : Dy exhibits an ESR line due to a defect centre. Thermal annealing behaviour indicates that this centre correlates with the TL peak at 142°C. The centre is characterized by an isotropic g-value of 2.0039 and is assigned to a 𝐹+ centre.

• Combustion synthesis of Eu2+ and Dy3+ activated Sr3(VO4)2 phosphor for LEDs

Combustion synthesis and photoluminescence (PL) characterization of Sr3(VO4)2:Eu,Dy phosphors are presented in this paper. PL emission of Sr3(VO4)2:Eu phosphor shows green broad emission band centring at 511 nm and a red sharp band at 614 nm by excitation wavelength of 342 nm. The PL emission spectrum of Sr3(VO4)2:Dy phosphor exhibits an intense blue emission peak at 479 nm, yellow broad band centring at 573 nm and red band at 644 nm by the excitation wavelength of 426 nm in near visible blue region. The excitation wavelength of Eu (342 nm) and Dy (426 nm) activated Sr3(VO4)2 phosphor are well matched with the excitation of near UV excited solid state lighting and blue chip excitation of light emitting diodes, respectively. The effect of Eu2+ and Eu3+ ions concentration on the emission intensity of Sr3(VO4)2 was also investigated. The Sr3(VO4)2:Eu is a potential green and red emitting phosphor as well as Sr3(VO4)2:Dy is blue and yellow emitting phosphor for solid state lighting i.e. white LEDs. The XRD and SEM characteristics of Sr3(VO4)2 materials was also reported in this paper.

• Ce and Eu activated Na2Zn5(PO4)4, a new promising novel phosphor

A new efficient phosphor, Eu2+/Eu3+ and Ce3+ activated Na2Zn5(PO4)4 has been synthesized by solid-state reaction technique at high temperature. X-ray powder diffraction analysis confirmed the formation of Na2Zn5(PO4)4 host lattice. Scanning electron microscopy indicated that the microstructure of the phosphor consisted of irregular fine grains with a size of about 0.5–2 𝜇m. Photoluminescence excitation spectrum measurements of Ce3+ activated Na2Zn5(PO4)4 show that the phosphor can be efficiently excited by UV-Vis light from 280 to 310 nm to realize emission in the visible (blue) range due to the 5𝑑–4𝑓 transition of Ce3+ ions which is applicable for scintillation purpose, whereas Eu2+/Eu3+ activated Na2Zn5(PO4)4 phosphor emits blue, green and red emission spectrum shows at 487 nm, 546 nm with a dominant peak at 611 nm respectively, due to Eu2+/Eu3+ ions which is promising candidate for solid state lighting. Therefore, newly synthesised, by low cost and easy technique prepared, novel phosphors may be useful as RGB phosphor for solid state lighting application.

• Synthesis and photoluminescence characterization of Ce3+ and Dy3+ activated ALa(WO4)2(A = Na and Li) novel phosphors

In this paper, we report the synthesis of Ce3+ and Dy3+ activated alkali lanthanide tungstates, ALa(WO4)2(where A = Na and Li), prepared by solid state reaction method. The prepared phosphors were characterized by X-ray diffraction and photoluminescence techniques. The NaLa(WO4)2:Dy3+ and LiLa(WO4)2:Dy3+ phosphors show two emission peaks at around 574 and 486 nm (𝜆exc = 354 nm). NaLa(WO4)2:Ce3+ and LiLa(WO4)2:Ce3+ show two emission peaks at around 378 and 425 nm (𝜆exc = 350 nm). Excitation wavelengths of Ce3+ and Dy3+ activated alkali lanthanide tungstates are in near UV region i.e. Hg free excitation. These characterizations of phosphors are applicable for solid state lighting. Accordingly, Ce3+ and Dy3+ activated NaLa(WO4)2 and LiLa(WO4)2 may be the promising materials for solid state lighting applications.

• Blue-shifted photoluminescence of Alq3 dispersed in PMMA

Alq3 is known to emit bright green light under UV excitation. Blue shift of the emission was reported in recent literature. This was ascribed to the presence of various isomers/crystallographic modifications obtained through train sublimation. Here a blue shift was reported for Alq3 dispersed in PMMA. No isomers/phases, which were reponsible for blue-shift, separated and yet the emission maxima shift to shorter wavelengths as the concentration of Alq3 in PMMA decreases. The results were interpreted on the basis of cross relaxation between interacting Alq3 molecules.

• Lyoluminescence in Ce3+ activated (KNa)Br phosphor for ionizing radiation dosimetry

The lyoluminescence (LL) in 𝛾-ray irradiated (KNa)Br : Ce3+ phosphors are reported in this paper. LL of (KNa)Br : Ce3+ have been recorded for different 𝛾-ray doses. The nature of variations of LL peak intensities is found to be linear with 𝛾-ray irradiation dose and LL peak intensity is found to be dependent on concentrations (0.1–10 mol%) of added Ce3+ ions in the (KNa)Br host lattice. Negligible fading in the prepared sample is observed.

• Photoluminescence properties of X5SiO4Cl6:Tb3+ (X = Sr, Ba) green phosphor prepared via modified solid state method

Luminescence property of a new halo silicate phosphor, X5SiO4Cl6:Tb3+ (X = Sr, Ba) prepared by modified solid state method is reported here. It is characterized by powder X-ray diffraction and studied by photoluminescence excitation and emission spectra. In the emission spectra of X5SiO4Cl6:Tb3+ (X = Sr, Ba) phosphor, characteristic blue and green emission peaks are present corresponding to Tb3+ intra 4𝑓 transition. Emission spectrum shows a dominant peak at 544 nm due to the ${}^{5}D_{4} \rightarrow {}^{7}F_{5}$ transition of Tb3+.

• # Bulletin of Materials Science

Volume 44, 2021
All articles
Continuous Article Publishing mode

• # Dr Shanti Swarup Bhatnagar for Science and Technology

Posted on October 12, 2020

Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020