Synthesis and luminescence properties of Cr₂O₃-CaO-GeO₂ glass and glass ceramics for broadband NIR-LEDs

Abstract

We report the fabrication of novel 0.1Cr2O3-25CaO-75GeO2 glass and glass ceramics with wideband NIR luminescence and the annealing temperature dependence of the photoluminescence (PL) properties for applications as NIR phosphors. The anisotropic growth of Ca2Ge7O16 nanocrystals in the annealing samples was confirmed. Annealing-induced variations in the body colors and diffuse reflectance spectra suggest that change in the valence of Cr ions and their coordination environments. Broadband luminescence of 700-1300 nm attributed to the 4T2 → 4A2 transition of Cr3+ was observed for the as-made glass. The peak wavelength is shifted from 860 to 780 nm, and line-shaped 2E → 4A2 emission appears due to the crystallization of Ca2Ge7O16 by heat treatment. The PL quantum efficiency reaches the maximum at 0.19 when the sample is annealed at 775ºC, and the dependence on annealing temperature can be understood by the change in the PL lifetimes and diffuse reflectance spectra.

Broadband NIR luminescence of Cr3+-doped Mg4Nb2O9 phosphors toward LED light source applications for NIR spectrometry

“…Phosphorconverted LEDs (pc-LEDs) are also used in white LEDs, and various NIR phosphors have recently been reported. [11][12][13][14][15][16][17][18][19] Several rare-Earth and 3D transition metal ions act as NIR luminescent centers in phosphors. Previously, we developed NIR glass phosphors with intra-4f shell luminescence using rare-Earth ions.…”

“…Meanwhile, NIR phosphors doped with Cr 3+ , identified as 3d transition metal ions, have been investigated. 15,19,22) The broadband luminescence of Cr 3+ can be explained by the Tanabe-Sugano diagram. 23) Figure 1 illustrates the Tanabe-Sugano diagram for the 3d 3 electron configuration in octahedral coordination.…”