Gallium nitride （GaN） is a cornerstone of third-generation wide-bandgap semiconductor technology， valued for its exceptional electronic mobility， thermal stability， chemical inertness， and robustness under extreme operating conditions. These qualities have driven its adoption in high-power electronics， high-frequency devices， and ultraviolet optoelectronics. However， a persistent challenge in GaN-based photonics is achieving efficient and stable red emission. Conventional InGaN-based red Light-Emitting Diodes （LEDs） suffer from efficiency droop and phase separation issues inherent to the high indium （In） content required for red wavelengths. As an alternative， doping GaN with rare-earth （RE） ions—which exhibit sharp， stable intra-4f shell emissions largely independent of the host matrix—offers a promising route to high-color-purity red light. Among these， trivalent europium ions （Eu³⁺） are renowned for their intense red emission lines around 620 nm. To enhance the optical activation and emission efficiency of such RE centers， co-doping with a sensitizer ion is a widely employed strategy. Samarium ions （Sm³⁺） have demonstrated effective sensitization of Eu³⁺ luminescence in various host materials through resonant energy transfer. Nevertheless， the specific system of Sm³⁺/Eu³⁺ co-doped GaN is still in its infancy. This study aims to systematically investigate the structural modifications and luminescence characteristics—particularly the energy transfer dynamics—in GaN thin films co-doped with Sm³⁺ and Eu³⁺ ions， thereby evaluating its potential as a novel red-emitting material platform compatible with established GaN semiconductor processes.

This research employed ion implantation as the doping technique to introduce Sm³⁺ and Eu³⁺ ions into high-quality GaN thin films grown on c-plane sapphire substrates via metal-organic chemical vapor deposition （MOCVD）. A series of samples were prepared： including Sm³⁺ single-doped samples with varying doses （1×10¹⁴， 5×10¹⁴， 1×10¹⁵ at/cm²）， and Sm³⁺/Eu³⁺ co-doped samples with a fixed Sm³⁺ dose （5×10¹⁴ at/cm²） and varying Eu doses （1×10¹⁴， 5×10¹⁴， 1×10¹⁵ at/cm²）. Post-implantation thermal annealing at 1 000 ℃ in an ammonia atmosphere was conducted to recover implantation-induced lattice damage and to optically activate the RE ions. The structural integrity and stress state of the doped films were comprehensively assessed using High-resolution X-ray Diffraction （HRXRD） and Raman spectroscopy. The optical emission properties were investigated using Cathodoluminescence （CL） spectroscopy.

HRXRD rocking curve analysis of the GaN （0002） plane revealed that the Full Width at Half Maximum （FWHM） increased with higher Sm³⁺ concentrations in single-doped samples， indicating a degradation of crystalline quality due to implantation-induced defects. In co-doped samples with a fixed Sm³⁺ dose， the FWHM exhibited a complex， non-monotonic trend as the Eu³⁺ dose increased， showing a slight initial decrease followed by a rise at higher doses. This suggests that the incorporation of a low dose of Eu³⁺ may induce minor lattice distortions that slightly improve local ordering， while higher doses exacerbate defect formation. Lattice constant analysis from 2θ/ω scans and Raman shift measurements of the E₂^high phonon mode provided consistent evidence of stress evolution. Sm³⁺ single-doping introduced tensile stress， whereas the introduction of Eu³⁺ in co-doped samples led to a significant increase in compressive stress， which intensified with higher Eu³⁺ doses.

Cathodoluminescence spectroscopy provided clear evidence of efficient energy transfer from Sm³⁺ （sensitizer） to Eu³⁺ （activator）. In Sm³⁺ single-doped samples， characteristic emission peaks were observed from Sm³⁺ at approximately 577 nm （⁴G_5/2 → ⁶H_5/2）， 618 nm （⁴G_5/2 → ⁶H_7/2）， and 666 nm （⁴G_5/2 → ⁶H_7/2）. In the co-doped samples， the Sm³⁺ emission intensity， particularly the 577 nm peak， was significantly quenched， while the characteristic Eu³⁺ emission lines， especially the dominant red emission at ~620 nm （⁵D₀ → ⁷F₂）， were strongly enhanced with increasing Eu³⁺ concentration. This anti-correlation provides clear evidence for a non-radiative energy transfer process. The primary energy transfer pathway was identified as ⁴G_5/2 （Sm³⁺） + ⁷F₀ （Eu³⁺） → ⁶H_5/2 （Sm³⁺） + ⁵D₀ （Eu³⁺）， favored by the near-perfect resonance （energy mismatch of only ~74 meV） between the Sm³⁺⁴G_5/2 → ⁶H_5/2 transition and the Eu³⁺⁷F₀→⁵D₀ absorption.

Further quantitative analysis based on Dexter's theory was conducted to elucidate the dominant interaction mechanism. By analyzing the dependence of the Sm³⁺ emission quenching ratio on the total RE concentration through fitting， it was determined that energy transfer occurs primarily via electric dipole-dipole and electric dipole-quadrupole interactions. Critical energy transfer distances （R_c） were calculated to lie between 1.66 nm and 2.24 nm for the studied concentration range， confirming the feasibility of efficient resonant transfer at these doping levels.

The impact of co-doping on the emitted light color was evaluated using the Commission Internationale de l'Éclairage （CIE） chromaticity coordinates. As the Eu³⁺ dose increased from 1×10¹⁴ to 1×10¹⁵ at/cm²， the CIE coordinates systematically shifted from （0.527 5， 0.369 5） in the yellowish-red region to （0.606 3， 0.353 2） in the deep red region. Correspondingly， the calculated Correlated Color Temperature （CCT） decreased from 1 580 K to 730 K. This demonstrates that by adjusting the concentration of Eu³⁺ relative to the fixed proportion of the Sm³⁺ sensitizer， a clear and controllable tuning of the emission color toward saturated red can be achieved.

In conclusion， this study successfully fabricated and characterized Sm³⁺/Eu³⁺ co-doped GaN thin films via ion implantation. Although the doping process introduces compressive stress and affects the crystalline quality， it enables efficient resonant energy transfer from Sm³⁺ to Eu³⁺. This transfer effectively pumps the Eu³⁺⁵D₀ level， resulting in intensified red emission around 620 nm. Most notably， the emission color can be tuned from yellowish-red to deep red by varying the Eu³⁺ concentration， providing a direct means to achieve targeted red chromaticity. These findings offer foundational experimental insights and a material processing framework for developing GaN-based red-emitting devices utilizing the Sm³⁺/Eu³⁺ co-doping scheme， presenting a potentially advantageous alternative to high-In-content InGaN for red micro-LEDs and other advanced optoelectronic applications. Future work may focus on optimizing implantation and annealing parameters to mitigate structural damage and further enhance the luminescence efficiency of this co-doped system.