Designing ultra-highly efficient Mn²⁺-activated Zn₂GeO₄ green-emitting persistent phosphors toward versatile applications

Developing highly efficient green-emitting phosphors is very significant because human eyes are sensitive to green spectral region. Herein, Mn²⁺-activated Zn₂GeO₄ phosphors, which can emit bright green light with an ultrahigh internal quantum efficiency of 98.5%, were prepared by a solid-state reaction technology in ambient atmosphere. At 323 nm irradiation, the emission spectrum shows a narrow band centered at 534 nm, which is ascribed to the ⁴T₁ → ⁶A₁ transition of Mn²⁺, with a full width at half maxima of 49.5 nm. Through monitoring the temperature-dependent photoluminescence emission intensity and decay time of Mn²⁺, we explored the thermometric properties of the resultant compound and found maximum relative sensitivities of Zn₂GeO₄:0.02Mn²⁺ phosphor are 4.90% K⁻¹ and 0.74% K⁻¹, respectively. Furthermore, green afterglow phenomenon is observed in the designed phosphors, and its mechanism is verified by discussing the thermoluminescence. Because of the excellent luminescence behaviors, various multimode luminescent patterns for information encryption are designed, including anticounterfeiting and fingerprint identification. Furthermore, using the prepared Zn₂GeO₄:0.02Mn²⁺ as green-emitting components, a white-light-emitting diode with suitable color coordinates, high color rending index (>90), and low correlated color temperature (5,000–6,000 K) was fabricated. These results demonstrate that Mn²⁺-activated Zn₂GeO₄ phosphors are multifunctional green-emitting components for optical thermometry, anticounterfeiting, fingerprint detection, and solid-state lighting applications.