The pH Value Control of Morphology and Luminescence Properties of Gd2O2S: Tb3+ Phosphors

Developing rare-earth doped oxysulfide phosphors with diverse morphologies has significant value in many research fields such as in displays, medical diagnosis, and information storage. All of the time, phosphors with spherical morphology have been developed in most of the related literatures. Herein, by simply adjusting the pH values of the reaction solution, Gd₂O₂S:Tb³⁺ phosphors with various morphologies (sphere-like, sheet-like, cuboid-like, flat square-like, rod-like) were synthesized. The XRD patterns showed that phosphors with all morphologies are pure hexagonal phase of Gd₂O₂S. The atomic resolution structural analysis by transmission electron microscopy revealed the crystal growth model of the phosphors with different morphology. With the morphological change, the band gap energy of Gd₂O₂S:Tb³⁺ crystal changed from 3.76 eV to 4.28 eV, followed by different luminescence performance. The samples with sphere-like and cuboid-like microstructures exhibit stronger cathodoluminescence intensity than commercial product by comparison. Moreover, luminescence of Gd₂O₂S:Tb³⁺ phosphors have different emission performance excited by UV light radiation and an electron beam, which when excited by UV light is biased towards yellow, and while excited by an electron beam is biased towards cyan. This finding provides a simple but effective method to achieve rare-earth doped oxysulfide phosphors with diversified and tunable luminescence properties through morphology control.