Spherical and rod-like Gd 2 O 3 :Eu 3 + nanophosphors—Structural and luminescent properties

Abstract

A comparative study of spherical and rod-like nanocrystalline Gd $_{\boldsymbol 2}$ O $_{\boldsymbol 3}$ :Eu $^{\boldsymbol{3+}}$ (Gd $_{\boldsymbol{1\cdot92}}$ Eu $_{\boldsymbol{0\cdot08}}$ O $_{\boldsymbol 3}$ ) 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 Gd $_{\boldsymbol 2}$ O $_{\boldsymbol 3}$ :Eu $^{\boldsymbol{3+}}$ . Upon calcinations at 800 $^{\boldsymbol\circ}$ C for 3 h, dominant cubic phase was achieved. The as-formed precursor hydrothermal product shows hexagonal Gd(OH) $_{\boldsymbol 3}$ :Eu $^{\boldsymbol{3+}}$ phase and it converts to pure cubic phase of Gd $_{\boldsymbol 2}$ O $_{\boldsymbol 3}$ :Eu $^{\boldsymbol{3+}}$ on calcination at 600 $^{\boldsymbol \circ}$ C for 3 h. TEM micrographs of hydrothermally prepared cubic Gd $_{\boldsymbol 2}$ O $_{\boldsymbol 3}$ :Eu $^{\boldsymbol{3+}}$ 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 Gd $_{\boldsymbol 2}$ O $_{\boldsymbol 3}$ :Eu $^{\boldsymbol{3+}}$ which has been assigned to $^{\boldsymbol 5}{\bf \textit{D}}_{\boldsymbol 0}$ $\boldsymbol \to$ $^{\boldsymbol 7}{\bf \textit{F}}_{\boldsymbol 2}$ transition. However, in hexagonal Gd(OH) $_{\boldsymbol 3}$ :Eu $^{\boldsymbol{3+}}$ , emission peaks at 614 and 621 nm were observed. The strong red emission of cubic Gd $_{\boldsymbol 2}$ O $_{\boldsymbol 3}$ :Eu $^{\boldsymbol{3+}}$ nanophosphors by hydrothermal method are promising for high performance display materials. The variation in optical energy bandgap ( $\boldsymbol{E}_{\boldsymbol{\rm g}}$ ) 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.