Alternative green gap tuning via Dy³⁺ → Tb³⁺ energy transfer of double-doped germanate glass and the variation of the UV illumination wavelength

This work analyzes the influence of dysprosium (Dy³⁺) and terbium (Tb³⁺) trivalent rare-earth ions on germanate (86GeO₂-14Na₂O) glasses for multicolor lighting applications. After evaluation of the optical properties of single-doped Dy³⁺ and Tb³⁺ glasses by the means of photoluminescence emission, excitation and time-resolved spectroscopy, the energy transfer mechanism of a double-doped glass (Dy³⁺/Tb³⁺) was evaluated. The double-doped sample exhibited a dominant dipole–dipole interaction in the Dy³⁺ → Tb³⁺ energy transfer process, and low probability for the Tb³⁺ → Dy³⁺ reverse transfer process. This enables multiple emission and excitation bands as a result of the interaction of both trivalent ions. The energy transfer process Dy³⁺ → Tb³⁺ promotes different optical emissions within the green-yellow region as a function of the illumination source wavelength, enabling a correlated color temperature (CCT) tuning from 3767 to 6333 K using UV illumination wavelengths from 285 to 393 nm.