Na₂MgAlF₇:Ln³⁺ (Ln³⁺ = Ce, Gd) weberite downshifting phosphor for designing UVB LED

New results on luminescence of Na₂MgAlF₇ activated with Ce³⁺ and/or Gd³⁺ are presented. Powder XRD confirms orthorhombic structure with Imm2 space group. Intense ultraviolet (UV) emission is observed for both the phosphors. Excitation for Gd³⁺ is in the form of narrow lines while a broad band marks the excitation spectrum for Ce³⁺. This broad band covers the most intense excitation line for Gd³⁺. By virtue of the close proximity of Ce³⁺and Gd³⁺ absorption, the former can act as a sensitizer for the latter. The excitation spectrum for Ce³⁺ also overlaps the emission from 275 nm UV chip. This was exploited for constructing phosphor converted UVB LED. Using Na₂MgAlF₇:Ce³⁺ phosphor and 275 nm UV chip, LED emitting broad band UVB light is demonstrated. Coating 275 nm chip with Na₂MgAlF₇:Ce³⁺, Gd³⁺phosphor, resulted in a LED with dominant emission at 311 nm. The results presented are important for obtaining UVB LEDs at lower prices.