Tunable rare-earth-free white light emission in zinc phosphate glasses activated with Ag_mⁿ⁺ clusters and Mn²⁺ ions

ZnO–P₂O₅ glasses activated with Ag_mⁿ⁺ clusters and Mn²⁺ ions were successfully synthetized by the melt-quenching method. X-ray diffraction patterns confirmed the glassy nature for doping concentrations up to 3.0 and 5.0 mol% of Ag⁺ and Mn²⁺ ions, respectively, whereas the Raman spectra in all cases displayed δ(P–O–P), ν_s(P–O–P), ν_s(PO₂) and ν_as(PO₂) vibrational modes, typical of a phosphate glass network. The emission spectra under 345 nm (Ag_mⁿ⁺: S₀ → S₁ and Mn²⁺: ⁶A₁(S) → ⁴T₁(P) + ⁴E(D)), 385 nm (Ag_mⁿ⁺: S₀ → S₁) and 407 nm (Mn²⁺: ⁶A₁(S) → ⁴A₁(G) + ⁴E(G) and Ag_mⁿ⁺: S₀ → S₁) excitations, showed the broad band related to the superimposed Ag_mⁿ⁺ cluster: S₁ → S₀, T₂ → S₀ and T₁ → S₀ radiative transitions along with the Mn²⁺: ⁴T₁(G) → ⁶A₁(S) one. Under 385 nm excitation, the Mn²⁺ emission transition is attained by energy transfer from Ag_mⁿ⁺ clusters. Such excitations lead to emission tonalities in the bluish white to cold white (345 and 385 nm) and cold white to reddish orange (407 nm) ranges, with correlated color temperature (CCT) values in the 10,095-5371 K (345 nm), 14,768-6862 K (385 nm) and 8592-1633 K (407 nm) ranges. Purplish pink emissions upon 345 nm excitation were obtained as well. The white color tonalities together with the color rendering index (CRI) and absolute quantum yield (QY, external) values up to 95 Ra and 35%, respectively, revealed promissory features for rare-earth-free white light emitting diode applications. The Ag_mⁿ⁺ cluster: S₁ → S₀ emission fitting by the Burstein model suggested that the non-radiative energy transfer is mainly mediated by an electric dipole-dipole interaction.