Tailoring the Morphology and Structure of Nanosized Zn₂SiO₄: Mn²⁺ Phosphors Using the Hydrothermal Method and Their Luminescence Properties

Abstract

Mn2+-doped Zn2SiO4 phosphors with nanoellipsoid or nanowire morphologies were synthesized at low temperature <200 °C by a hydrothermal method without any surfactants. The morphologies of the phosphors were easily tailored by varying the amount of hydroxide ions in the precursor solution before the hydrothermal reaction. Absolute ethanol was used as a solvent instead of distilled water to explore the effects of hydroxide ions on the morphology and crystal structure. We adjusted the amount of hydroxide ions by changing the pH of the precursor solution. Sheaves of powders with an ellipsoid shape were synthesized at low pH values of 7 and 9, at which only a few hydroxide ions were present, whereas powders with a nanowire shape were produced at a high pH of 11, at which many hydroxide ions were present. In addition to its morphology, the hydroxide ions also affect the crystal structure of the synthesized powder. Whereas a Zn2SiO4 phase with a willemite structure was formed at pH 7 and 9, a Zn4Si2O7(OH)2·H2O phase with a hemimorphite structure was formed at pH 11. The as-prepared powders with a willemite structure showed an intense green emission (λ ≈ 525 nm) under 254 nm excitation, whereas the as-prepared powders with a hemimorphite structure did not show any emission. However, all of the powders showed a willemite structure while retaining their original shape after annealing at 900 °C under a reducing atmosphere. The annealed sheaves of willemite with an ellipsoid shape showed a more intense green emission with a longer decay time than the phase-transformed willemite nanowires. These results were discussed in terms of the surface defects and dopant concentration.

Effects of Calcination Holding Time on Properties of Wide Band Gap Willemite Semiconductor Nanoparticles by the Polymer Thermal Treatment Method

“…Similarly, the particle size of the willemite produced by Al–nidawi et al [36] were at the range between 500–1000 nm, and this involved high temperature up to 1400 °C. The willemite NPs synthesized by hydrothermal methods generally involves low calcination temperature between 200–700 °C [37,38,39]. For instance, Zeng et al [37] synthesized non–uniformly distributed particles of willemite sized between 200–300 nm at the sintering conditions of 230 °C for 12 h. The same procedure was used by Xu et al [40].…”

A simple sonochemical approach for synthesis and characterization of Zn2SiO4 nanostructures

“…Willemite Zn 2 SiO 4 is a natural orthosilicate with a phenacite-like structure in which ZnAO tetrahedra and SiAO tetrahedra share corners to form hollow 'tubes' parallel to [0 0 0 1] [17,18]. The numerous investigations on the synthesis routes of Zn 2 SiO 4 have been carried out, including sol-gel method [19], solid-state route [20], polymer precursor method [21], spray pyrolysis method [22] and hydrothermal method [23,24]. However these methods usually require high pressure or heat-treating at temperatures higher than 180°C for several hours.…”

Microwave‐Assisted Hydrothermal Synthesis of Submicrometer Willemite Phase Zinc Silicate and Its Zinc Ion Release Behavior

“…Wang et al ., reported that ZSO firstly formed in the hydrothermal procedure, then ZSO would transform to ZS if it had a higher temperature or a longer reaction time in this step. An et al., suggested that ZSO tended to form at a higher pH value, and ZS would form at relatively low pH value (7 or 9) because of the deficiency of the hydroxide ions. However, our study indicates that the reactant concentration plays a significant role in the phase of final products.…”