Optical properties of CaSrSiO₄:Eu²⁺ phosphors prepared by using a solid-state reaction method for white light-emitting diodes

Abstract

We have studied the optical properties of CaSrSiO₄:Eu²⁺ phosphors synthesized by using the conventional solid-state reaction method and the role of Eu³⁺ minority ions in those phosphors. The maximum photoluminescence integrated peak intensity was observed for the Ca_1−x Sr_1−x SiO₄:2xEu²⁺ (2x = 0.0050) phosphor. A red shift of 3 nm from 510 to 513 nm in the emission wavelength of the CaSrSiO₄:Eu²⁺ phosphors was observed with increasing Eu concentration. Under an excitation of 244 nm, the Ca_1−x Sr_1−x SiO₄:2xEu²⁺ (2x = 0.0050) phosphor showed a broad emission band at about 515 nm due to the 4f ⁶5d ¹ → 4f ⁷ transition of the Eu²⁺ and small sharp peaks at about 594, 612, and 701 nm corresponding to the 5D ₀-⁷ F _J transitions of Eu³⁺. The existence of Eu³⁺ minority ions in the phosphor resulted in a broader full width at half maximum in the emission of the phosphor at the excitation wavelength of 390 ~ 400 nm, even at low Eu concentration. The white light-emitting diodes (LEDs) were fabricated by using the CaSrSiO₄:Eu²⁺ phosphors and 400-nm GaN-based LED chips and exhibited a high color rendering index of ~ 95 and correlated color temperature of ~ 5370 K. The broad emissions of the CaSrSiO₄:Eu²⁺ phosphors combined with the GaN-based LED chips are suitable for the realization of white LEDs.