Optical characterization of GaN:Eu microcrystals grown by the ammonothermal method

Abstract

Eu-doped gallium nitride (GaN:Eu) microcrystals with a wurtzite crystal structure were synthesized using the ammonothermal method. The Eu concentration of GaN:Eu microcrystals estimated by glow discharge mass spectrometry (GDMS) was 5.8 × 1020 atoms/cm3. The morphology of GaN:Eu microcrystals was characterized by scanning electron microscopy (SEM). The exposed crystal faces of GaN:Eu microcrystals were identified as {10−10}, {10−11}, (000−1), and (0001), respectively. The photoluminescence excitation (PLE), photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectra of GaN:Eu microcrystals revealed two luminescent sites of Eu3+ ions, designated as Eu0 and Eu1. The Eu0 was excited in the range of 300 nm to 420 nm, resulting in the observation of four characteristic luminescence peaks at 599 nm (5D0-7F1), 620 nm (5D0-7F2), 632 nm (5D1-7F4), and 663 nm (5D0-7F3). The Eu1 was associated with O2- ions and emitted light at specific excitation wavelengths. The main luminescence peak of the Eu1 was located at 614 nm, accompanied with characteristic peaks at 578 nm, 591 nm, and 698 nm. In view of the distinct luminescence properties of the Eu0 and the Eu1, the energy transfer processes of two luminescence sites were proposed.