Comprehension of the photoinduced charge transfer assisted energy transfer in Gd3+-based host sensitized tellurate phosphors for thermal sensing and anticounterfeiting labels

Abstract

A series of novel Eu³⁺-activated Ba₂Gd_2/3TeO₆ (BGT) phosphors were successfully synthesised via a high temperature solid state reaction method. The crystal structure analysis showed that Eu³⁺-doped Ba₂Gd_2/3TeO₆ double perovskite phosphors possess monoclinic symmetry with space group P2₁/n. The as-prepared phosphors can be efficiently excited by far-ultraviolet light to generate reddish orange luminescence of around 593 nm corresponding to the ⁵D₀ → ⁷F₁ transitions of Eu³⁺ ions. Gd³⁺ acts as a sensitizer for luminescence enhancement. The highest luminescence intensity corresponded to x = 0.11 Eu³⁺ concentration, and the critical distance was calculated to be 9.61 Å, indicating that multipolar interaction is behind the concentration quenching mechanism. Besides, the optimum concentration Eu³⁺-activated Ba₂Gd_2/3TeO₆ phosphor exhibited color co-ordinates of (0.63, 0.36), a high color purity of 94.21% and a quantum efficiency of 18%. JO intensity parameters reveal the slight distortion of the crystal field around the activator ion. Notably, the maximum relative sensitivities of the BGT:0.11Eu³⁺ phosphor were found to be 0.19% K⁻¹ within the temperature range of 300–500 K and 2.07% K⁻¹ within 80–300 K, and it can potentially be used as a promising thermometer in high and low temperature regions, respectively. The luminescent labels based on fluorescent ink and PL chalk demonstrate the potential application of synthesized phosphors in anti-counterfeiting and security labeling.