Atmospheric AACVD Growth of Nd ³⁺ : ZnO Thin Films With Temperature‐Optimized Crystallinity and Up‐Conversion Quantum Yield

Thin films doped with rare‐earth ions often suffer from poor crystallinity and low up‐conversion quantum yield (UCQY), limiting their use in photonic and energy‐conversion devices. Nd ³⁺ ions remain particularly underexplored when doped in thin‐film, with no established route for achieving efficient visible up‐conversion (UC). Here, we develop an aerosol‐assisted chemical vapor deposition (AACVD) process operated at atmospheric pressure to fabricate Nd ³⁺ ZnO thin films on Si(111). Systematic variation of the deposition temperature (370–500°C), followed by post‐annealing at 1000°C, reveals a direct correlation between Nd incorporation, ZnO crystallinity, and UCQY. Films deposited at 430°C incorporate 2.97 at.% Nd and exhibit optimal c ‐axis orientation and a refractive index of ~2.03. Under 808 nm excitation, these films display strong visible UC emissions at 540, 618, and 680 nm, achieving a total UCQY of 4.25 ± 0.1%. Mechanistic analysis indicates a two‐photon process involving excited‐state absorption (ESA), energy transfer (ET), cooperative energy transfer (CET), and cross‐relaxation (CR), with concentration quenching occurring above ~3 at.% Nd. This study presents a temperature‐dependent AACVD method that optimizes Nd incorporation and ZnO microstructure for efficient visible UC. This provides a cost‐effective and scalable pathway for high‐performance Nd‐activated photonic thin films.