Broadband near-infrared (NIR) emission realized by the crystal-field engineering of Y3−xCaxAl5−xSixO12:Cr3+ (x = 0–2.0) garnet phosphors

Abstract

The rapid development of portable spectrometers has evoked a large demand for minimized light sources; meanwhile, NIR phosphor-converted light-emitting diodes (NIR pc-LEDs) are an optimal choice due to their compactness and low cost. The phosphors used in NIR spectroscopy (NIRS) are required to have broadband emission and high quantum efficiency (QE) for a wider detection range and efficient photo-to-electricity conversion. Inspired by the structural tunability of Y₃Al₅O₁₂ (YAG), we proposed to achieve broadband emission by crystal field engineering, i.e., indirectly regulating the crystal field strength of Cr³⁺via the co-substitution of Y³⁺–Al³⁺ by Ca²⁺–Si⁴⁺ in YAG. The crystal field strength experienced on Cr³⁺ decreased as the octahedron was distorted and enlarged by the co-substitution. A broadband NIR emission with a large full width at half maximum (FWHM) of 160 nm and a high internal quantum efficiency (IQE) of ∼75.9% was realized in Y_3−xCa_xAl_5−xSi_xO₁₂:0.6% Cr (x = 1). The suitability of the investigated NIR phosphor was demonstrated by fabricating an NIR pc-LED prototype, and the detection resolution was improved by 30% compared to that of a traditional white pc-LED. These results indicate the great potential of the Y₂CaAl₄SiO₁₂:Cr phosphors for use in highly precise and sensitive NIR pc-LEDs.