• H Nagabhushana

      Articles written in Bulletin of Materials Science

    • Spherical and rod-like Gd2O3:Eu3+ nanophosphors—Structural and luminescent properties

      N Dhananjaya H Nagabhushana B M Nagabhushana B Rudraswamy C Shivakumara R P S Chakradhar

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      A comparative study of spherical and rod-like nanocrystalline Gd2O3:Eu3+ (Gd1.92Eu0.08O3) red phosphors prepared by solution combustion and hydrothermal methods have been reported. Powder X-ray diffraction (PXRD) results confirm the as-formed product in combustion method showing mixed phase of monoclinic and cubic of Gd2O3:Eu3+. Upon calcinations at 800°C for 3 h, dominant cubic phase was achieved. The as-formed precursor hydrothermal product shows hexagonal Gd(OH)3:Eu3+ phase and it converts to pure cubic phase of Gd2O3:Eu3+ on calcination at 600°C for 3 h. TEM micrographs of hydrothermally prepared cubic Gd2O3:Eu3+ phase shows nanorods with a diameter of 15 nm and length varying from 50 to 150 nm, whereas combustion product shows the particles to be of irregular shape, with different sizes in the range 50–250 nm. Dominant red emission (612 nm) was observed in cubic Gd2O3:Eu3+ which has been assigned to ${}^{5}D_{0} \rightarrow {}^{7}F_{2}$ transition. However, in hexagonal Gd(OH)3:Eu3+, emission peaks at 614 and 621 nm were observed. The strong red emission of cubic Gd2O3:Eu3+ nanophosphors by hydrothermal method are promising for high performance display materials. The variation in optical energy bandgap (𝐸g) was noticed in as-formed and heat treated systems in both the techniques. This is due to more ordered structure in heat treated samples and reduction in structural defects.

    • Red luminescence from ZnO : Cr3+ nanophosphors under visible excitation

      N Pushpa M K Kokila B M Nagabhushana H Nagabhushana A Jagannatha Reddy

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      ZnO : Cr3+ (1 mol%) nanophosphor is synthesized by the wet chemical solution combustion method at the temperature of 400°C. Powder X-ray diffraction results confirmed that Cr3+-doped and undoped ZnO nanophosphors exhibit hexagonal wurtzite structure. The average crystallite size calculated from Scherrer’s method is 25 nm for undoped and 14 nm for Cr3+-doped ZnO. The UV–visible absorption spectra shows red shift in Cr3+-doped ZnO. Photoluminescence studies of undoped ZnO show violet emission peak at 400 nm and blue emission peak at 447 nm. Cr3+-doped ZnO shows red emission peaks at 642, 694 and 746 nm, which are mainly attributed to spin forbidden transitions of $^2$Eg $\to {}^4$A2g of Cr3+ ion in ZnO : Cr3+ nanophosphor. Thermoluminescence (TL) studies recorded at a heating rate of 6°C s$^{–1}$ show two well-resolved glow peaks at 124 and 284°C. It is found that the TL intensity increases with the gamma irradiation dose (500 Gy–10 kGy).

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