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

Abstract

In this work, a series of novel NaLa_1−xGd_xCa₄W₂O₁₂:Mn⁴⁺ (NL_1−xG_xCWO: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.