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

Abstract

Herein, we report the photoluminescence (PL) properties of Cr3+-doped Mg4Nb2O9 phosphors for applications in NIR phosphor-converted LEDs. Trigonal Mg4Nb2O9 crystals with Cr3+ substitution at three sites were synthesized as the main phase using a solid-state reaction. X-ray photoelectron spectrometry and diffuse reflectance spectroscopy indicated that only trivalent chromium ions were present in the samples. Broadband NIR emission of Cr3+ suitable for combination with Si photodetectors was confirmed at approximately 850 nm. The maximum PL quantum yield (PLQY) was 0.62, and concentration quenching explained the Cr concentration dependence of the PLQY and PL decay time. Low-temperature PL measurements suggested that the PL spectrum comprised three distinct emission bands. The results of the phonon line simulation, low-temperature photoluminescence excitation measurements, and crystal-field parameter estimation clarified the correlation between these emission bands and the Cr3+ substitution sites.