Photoluminescence of SiO2:Eu and SiON:Eu films: Color selection through activating emissions from SiOx, Eu3+, and Eu2+

Abstract

Photoluminescence (PL) from Eu-doped SiO2 (SiON) thin films sputter-deposited in O2, H2O vapor, or a mixture of O2 and N2 gases was characterized by excitation at a wavelength of 325 nm. The SiO2 films deposited at 500 °C with O2 contained small amount of α-quartz nanocrystals. The primary condition for either or both of the Eu3+ and Eu2+ emissions to appear was Eu content between 1 and 3 at.%, and 2.5 at.% gave the maximum emission intensity of Eu3+. The PL spectra showed only the Eu3+ emission when the films were deposited at room temperature (RT) and subsequently post annealed in an O2 atmosphere. Changing the annealing atmosphere from O2 to a vacuum and annealing at temperatures above 600 °C resulted in an intense broad violet emission signal peaking at 390 nm along with the Eu3+ emission signal. This violet emission originated from reduced SiOx species. When deposited at RT, similar temperature-dependent emission properties were obtained regardless of the reactive gas (H2O vapor or a mixture of O2 and N2). Complete transformation of Eu3+ into Eu2+ occurred when deposition was carried out at temperatures between 400 and 500 °C; a blue emission at around 467 nm was predominant from the SiO2:Eu2+ films. Deposition in the O2 and N2 gas mixture at elevated temperatures produced SiON:Eu2+ films, from which an intense white emission band peaking at 525 nm and ranging between 400 and 650 nm was observed.