Visible light emission and control by infrared-responsive materials

Upconversion characteristics of rare-earth cations were utilized for emitting or controlling visible light with infrared light. A fluorescent glass rod was fabricated by using durable AlF3-based glass that contained high-concentration Er3+ cations. This glass rod acted as a two-way wavelength converter; i.e., visible light (~500 nm) was converted to infrared light (~800 nm) as it passed through the glass, and infrared light that propagated in the opposite direction was converted to visible light. An infrared-responsive photochromic compound was fabricated by dispersing spirobenzopyran and upconversion powder (Gd2O2S:Yb3+Er 3+) in photocurable acrylate. When this compound was exposed to ultraviolet light (~370 nm), a strong absorption band appeared in the visible spectral region due to photochromic isomerization of spirobenzopyran. This absorption band disappeared by irradiation of a 940-nm laser beam, since the upconversion powder emitted green light that caused bleaching of colored spirobenzopyran.