Hydrothermal synthesis and photoluminescence of SrWO₄:Tb³⁺ novel green phosphor

Abstract

Tb³⁺-doped SrWO₄ phosphors with a scheelite structure have been prepared by hydrothermal reaction. X-ray powder diffraction, field-emission scanning electron microscopy, photoluminescence excitation and emission spectra and decay curve were used to characterize the resulting samples. Scanning electron microscopy image showed that the obtained SrWO₄:Tb³⁺ phosphors appeared to be nearly spherical and their sizes ranged from 1 to 3 μm. Photoluminescence spectra indicated the phosphors emitted strong green light centered at 545 nm under ultraviolet light excitation. Because 12 at.% SWO₄:Tb³⁺ phosphor exhibits intensive green emission under 254 nm excitation in comparison with the commercial green fluorescent lamp phosphor (LaPO₄:Ce,Tb), the excellent luminescence properties make it a new promising green phosphor for fluorescent lamps application.

Introduction

Luminescent materials containing rare-earth ions have become popular in the progress of the optical material of significant importance [1], [2], [3], [4]. Commercial powder phosphors are usually based on the host matrices of tungstates [5], phosphates [6], borates [7], silicates [8] and aluminates [9] etc. Among them, tungstates have two types of structure: wolframite and scheelite. Strontium tungstate has the scheelite structure which is tetragonal with space group I41/a ($C_{4h}^6$) [10]. The luminescent properties of strontium tungstate have been extensively investigated because it is a widely used in a variety of fields, such as laser materials [11], microwave ceramics [12], and photoluminescence [13].

At present, the traditional synthesis for commercial green fluorescent lamp phosphors (LaPO₄:Ce,Tb) is usually solid-state reaction over 1100 °C, including a long processing time and reducing atmosphere [6]. Moreover, the LaPO₄:Ce,Tb phosphor particles prepared by the conventional solid-state reaction method had large size and irregular morphology. Therefore, it is important to develop new processing material method with low costs, environmentally friendly and with possibility of formation of materials on macro- and nanoscale with well-defined morphologies, such as sol–gel process [14] and hydrothermal method [15]. There have been some reports about the hydrothermal synthesis and properties of the alkaline-earth tungstate materials, all of them were concentrated on pure SrWO₄ [16] and Eu³⁺-doped CaWO₄ [15], [17]. But to the best of our knowledge, hydrothermal synthesis and photoluminescence properties of SrWO₄:Tb³⁺ phosphors have not yet been reported till now.

In this paper, we report the preparation of SrWO₄:Tb³⁺ spherical phosphors with different Tb³⁺-doped concentration by a mild hydrothermal method. The luminescence properties of SrWO₄:Tb³⁺ phosphors were investigated by changing doping concentration of Tb³⁺ ions in the host. Our results show that SrWO₄:Tb³⁺ has good properties as a green phosphor for fluorescence lamps application.