Saturation of phosphors under low‐voltage excitation

— Two potential green FED phosphors, Gd 2 O 2 S:Tb and SrGa 2 S 4 : Eu, are examined in detail for performance at 1000‐V excitation energy. Strong saturation effects are observed in Gd 2 O 2 S:Tb and this is explained in terms of ground‐state depletion resulting from the relatively small volume of activators available. A simple two‐level model is used to show that ground‐state depletion can be observed by analyzing the rise time of the luminescence during the “pulse on” excitation time. A comparison is made between the efficiencies of both phosphors as a function of current density, and the article concludes by demonstrating that fast‐decay‐time phosphors such as SrGa 2 S 4 : Eu (1/e = 500 ns) may be essential to enable 100‐cd/m 2 displays at low voltage.