Structural and Luminescent Properties of GaN：Eu，Dy Films

With the global energy shortage，solid light-emitting materials with high efficiency，energy saving and environmental protection has become more and more important in lighting materials. Among them，GaN-based semiconductor light-emitting diodes （LEDs）have been developed rapidly. Traditionally，GaN-based LEDs changed the emission wavelength by changing the content of In component. At present，due to the phase segregation of In，low mutual solubility，and the fact that the spectral lines were easily affected by current and other factors，the commercialization of white LEDs and red LEDs was in progress. Rare earth（RE）ions could undergo radiation transitions in their 4f electron layers，and are not easily affected by the external environment. The emitted light was stable，monochromatic，high-intensity. Therefore，the doping of rare earth ions in GaN host would avoid the above-mentioned traditional GaN-based LEDs question. Dysprosium（Dy）ions could emit blue and yellow light，but the red light was weak. Europium（Eu）ions could emit bright red light. The co-doping of Eu and Dy was expected to achieve white and other visible light emission. In this paper，a series of Eu，Dy doped GaN samples were prepared by ion implantation. Their structure，luminescence and energy transfer mechanism were investigated. GaN thin films were epitaxially grown by metal-organic chemical vapor deposition（MOCVD），and then GaN thin films were uniformly doped with different doses of Eu and Dy ions by ion implantation. Finally，the samples were placed at 1000 ℃ in a flowing NH3 atmosphere for high temperature annealing treatment that was used to repair lattice damage and activate rare earth ions. The structural and luminescent properties of GaN：Eu，Dy were analyzed by Raman scattering spectroscopy，X-ray diffraction（XRD）patterns and cathodoluminescence spectroscopy. The energy transfer mechanism in GaN：Eu，Dy was calculated and analyzed according to Dexter multipole energy transfer theory and Reisfeld approximation theory. And the luminescence color change was analyzed by chromaticity coordinates and McCamy color temperature approximate equation. In addition，the structure and luminescence changes caused by different Eu and Dy implantation doses in GaN were also investigated. Raman and XRD results unanimously indicated that GaN lattice firstly formed tensile strain and subsequently formed compressive strain with the increase of Dy dose when Eu dose was constant. When Dy dose was 5×1014 at·cm-2，the lattice expansion of the sample was the smallest. So，the crystal quality was the best at this time. Eu and Dy co-doped GaN showed the same cathodoluminescence characteristics as Eu or Dy single-doped GaN，which indicated co-doping did not change the local crystal field. In the GaN host，625 nm emission peak corresponds to 5D0→7F2 transition was the strongest emission of Eu ions. 583 nm emission peak corresponded to 4F9/2→6H13/2 transition was the strongest emission of Dy ions. 583 nm emission gradually strengthened and 625 nm emission gradually weakened with the increase of Dy dose when Eu dose was constant. This showed that the change in the number of luminescent centers and the co-doping of rare earth ions would affect the luminescence of GaN：Eu，Dy，and there was energy transfer（Eu→Dy）between Eu ions and Dy ions. Further，through combining with calculation，Eu ions transfer energy to Dy ions by electron multi-pole interaction. In the spectrum，there were not intrinsic luminescence peaks of GaN，which indicated that the energy in GaNwas transferred to Eu and Dy to enhance the luminescence intensity of rare-earth ions. It also indicated that GaN provided an excellent platform for rare-earth ion luminescence. In the end，through the calculation of chromaticity coordinates and color temperature，it was found that with the change of ion implantation dose，the emission color changed between white and red，and the color temperature changed between 3889~4839 K. When Eu dose was 1×1014 at·cm-2，and Dy dose was 5×1014 at·cm-2，the chromaticity coordinates of the sample were（0.3373，0.3312）. The chromaticity coordinates of the sample were（0.3367，0.3253）when Eu dose was 1×1015 at·cm-2，and Dy dose was 1×1015 at·cm-2. They approached the standard white light chromaticity coordinates（0.3300，0.3300），and the color temperatures of the two samples were 4838 and 4839 K，respectively. In this paper，the white light emission with lower color temperature was achieved by optimizing the injection dose ratio of Eu and Dy，which also provided an experimental basis for the new GaN-based white light LED. This paper also suggested that the emission color could be regulated by co-doping various rare earth ions and changing the implantation ratio of rare earth ions，which also provided an experimental basis for the regulation of emission color by co-doping GaN with more rare earth ions in the future. © 2023 Editorial Office of Chinese Journal of Rare Metals. All rights reserved.