Fig. 1. Structures of GaN∶Eu³⁺ materials prepared by methods of in-situ growth and ion implantation. (a) In-situ growth; (b) ion implantation

Fig. 2. Room temperature PL spectra of the samples grown at 10 kPa and 100 kPa^[15]

Fig. 3. Room temperature CL spectra of GaN∶Eu³⁺ annealed at 1100, 1200, and 1300 ℃^[21]

Fig. 4. EL spectra at different bias voltages^[24]. (a) Yellow light emission at bias voltage of -100 V; (b) orange light emission at bias voltage of -70 V

Fig. 5. EL spectra of blue, green, and red light emissions from GaN∶Tm³⁺, Er³⁺, Eu³⁺ samples at bias voltages of -70 V and -100 V^[26]

Fig. 6. Energy transfer diagram of GaN∶Eu³⁺/Er³⁺ samples^[29]

Fig. 7. PL spectra for ⁵D₀→⁷F₂ transition of Eu³⁺ in GaN∶Eu³⁺/Mg²⁺ under above bandgap excitation at RT^[31]

Fig. 8. PL spectra at 25 K for GaN∶Eu³⁺/Mg²⁺ films with Eu³⁺ ion concentrations of 3×10¹⁸, 3×10¹⁹, and 3×10²⁰ cm^{-3 [36]}

Fig. 9. PL spectra of samples GaN∶Eu³⁺ and GaN∶Eu³⁺/Mg²⁺ at room temperature with doped ion dose (Eu³⁺ and Eu³⁺, Mg²⁺) of 5×10¹⁴ cm^{-2 [37]}

Fig. 10. PL spectra of the p-GaN samples^[42]. 1—GaN∶Mg²⁺, 2—GaN∶Eu³⁺/Mg²⁺, and 3—GaN∶Eu³⁺/Mg²⁺/Zn²⁺. PL in the long-wavelength is shown in the inset: 1—GaN∶Eu³⁺/Mg²⁺/Zn²⁺and 2—GaN∶Eu³⁺/Mg²⁺