Insight into emission-tuning and luminescence thermal quenching investigations in NaLa1-xGdxCa4W2O12:Mn4+ phosphors via the ionic couple substitution of Na+ + Ln3+ (Ln = La, Gd) for 2Ca2+ in Ca6W2O12:Mn4+ for plant-cultivation LED applications.

In this work, a series of novel NaLa1-xGdxCa4W2O12:Mn4+ (NL1-xGxCWO:Mn4+, x = 0-1) phosphors were synthesized using a high-temperature solid-state reaction approach. Unexpected intense red-far-red emissions were clearly observed after the ionic couple substitution of 2Ca2+ by Na+ + Ln3+ (Ln = La, Gd) in negligible-luminescence Ca6W2O12:Mn4+ upon ultraviolet (UV) excitation. Moreover, a maximal emission-tuning of Δλ = 28 nm (Δν = 582 cm-1) can be found by changing x from 0 to 1, which is ascribed to the different crystal field and covalence among them. In addition, the luminescence thermal quenching behaviors and thermal quenching mechanisms were investigated in detail in representative NLCWO:0.01Mn4+ and NGCWO:0.01Mn4+ phosphors. The results were used to initiate an ionic couple substitution strategy to enrich novel oxide hosts for Mn4+ luminescence and select an appropriate host with better thermal stability for plant-cultivation LED applications.