Blue, green and red emission from Ce3+, Tb3+ and Eu3+ ions in amorphous GaN and AlN thin films

We report strong blue, green and red emission from Ce3+, Tb3+ and Eu3+ ions, respectively, at room temperature in amorphous GaN and AlN thin films prepared by DC magnetron co-sputtering. We observe sharp characteristic emission peaks of intra-4f-shell transitions of the Tb3+ ions (5D4→7F3,4,5,6 transitions) and Eu3+ ions (5D0→7F1,2,3,4 transitions) and a strong but broad peak of 5d–4f emission from Ce3+ ions over the temperature range 2–300 K. The photoluminescence decay time from the excited 5D4 state of Tb3+ ions in a-AlN is 1.1 ms, which is similar to the radiative lifetime of this state in glasses. The broad photoluminescence peak centered at ∼400 nm in a-GaN shows a weak temperature dependence and may be attributed to the intrinsic tail-to-tail transitions in the amorphous matrix. The possible origin of the deep states, close to midgap in a-AlN, is briefly discussed.