Improvement in the dual-mode multicolor luminescence of the NaAlSiO4:Er3+, Yb3+ phosphors and the mechanistic investigations

Na 0.90- y AlSiO 4 :0.1Er 3+ , y Yb 3+ (0 ≤  y  ≤ 0.007) phosphors were prepared by the solid state reaction method and their dual mode multicolor luminescence properties were systematically investigated. The phosphors were crystallized into the carnegieite polymorph of NaAlSiO 4 at 1300 °C. The synthesized phosphors were characterized by using powder XRD technique, FT-IR and UV-VIS-NIR diffuse reflectance spectra. Upon 380 nm excitation, the phosphors emitted visible and NIR downconversion emission, which follows the quantum cutting process. The upconversion emission spectra , irrespective of the laser excitation wavelength (980 nm, 808 nm, or 1550 nm), show characteristics sharp green, and red emissions, from 2 H 11/2  →  4 I 15/2 , 4 S 3/2  →  4 I 15/2 , and 4 F 9/2  →  4 I 15/2 transitions of Er 3+ , respectively. Intense green (552 nm), red (664 nm) and NIR (809 nm) emissions were observed at 980, 808 and 1550 nm laser excitation, respectively. The dual mode emission of the Na 0.90- y AlSiO 4 :0.1Er 3+ , y Yb 3+ (0 ≤  y  ≤ 0.007) phosphors is enhanced upon Yb 3+ co-doping. By analyzing the dependence of upconversion emission intensities on the laser excitation power, a possible upconversion emission mechanism is proposed.