Saturation of phosphors under low‐voltage excitation

Two potential green FED phosphors, Gd2O2S:Tb and SrGa2S4: Eu, are examined in detail for performance at 1000‐V excitation energy. Strong saturation effects are observed in Gd2O2S: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 SrGa2S4: Eu (1/e = 500 ns) may be essential to enable 100‐cd/m2 displays at low voltage.