Significant colour tuning via energy transfer in Eu2+ solely doped La2.5Ca1.5Si12O4.5N16.5

Abstract

Eu²⁺ doped La_2.5Ca_1.5Si₁₂O_4.5N_16.5 powders have been prepared via a solid-state reaction synthesis and have been studied as a function of the Eu concentration. A large shift of the position of the Eu²⁺ 5d–4f emission band from 495 to 575 nm was observed with increasing Eu concentration, which changes the emission colour of the phosphors from blue-green for low Eu concentrations towards orange for highly concentrated samples. Similarly, the maximum in the excitation spectrum shifted from 388 to 511 nm. The shifts are due to the two distinct crystallographic sites on which the Eu²⁺ ions are substituted, which give rise to a high and a low energy emission band. Increased energy transfer at higher Eu concentration from the high to the low energy sites results in a relative increase of the low energy site emission. Temperature dependent luminescence measurements reveal a slight blue shift of the luminescence with increasing temperature due to energy back-transfer and show that the emission is temperature stable with half of the luminescence maintained up to 600 K.