Shining Transparent Displays with Stable Narrow-Band Blue-Emitting Phosphor in Layered Film

Transparent displays (TDs) rendering "levitating" images on screen have appeared as an emerging technology toward augmented/mixed reality applications. However, the traditional phosphor design and screen construction have severely limited the TD performance owing to the lack of efficient narrow-band blue emitters and stable screen structure. Herein, the novel narrow-band (full width at half maximum: 32 nm) NaLi₃ SiO₄ :Eu²⁺ phosphor with a peak at 467 nm as a key blue emitter is explored, and it is sandwiched in layered film as a unique screen design. The devised screen features decent transparency, high emission color purity, and good reliability, and the TD prototype renders "floating" static images and vivid animation with broad viewing angle (15°-165°) and large color gamut (97% of National Television Standards Committee). Spectroscopic and microstructural characterizations reveal the TD superior performance originates from synergistic contributions of moderate crystal field effect (ε_c  ≈ 1.13 eV; ε_cfs  ≈ 1.60 eV), weak vibronic coupling (S ≈ 3; ħω ≈ 285 cm^-1 ), and limited thermal ionization of 5d electrons (E_a  ≈ 0.43 eV) for NaLi₃ SiO₄ :Eu²⁺ emission and layered architecture for screen film. These findings establish fundamental guidelines for narrow-band emitting materials design and shine light on superior TD innovative development.