Eu2+induced crystal field modulation and luminescence enhancement in Ca9Ga(PO4)7:Zn2+,Cr3+

The development of efficient dual-emissive and temperature-sensitive luminescent materials is critical for advancing non-contact optical thermometry. Herein, we employed a co-doping strategy to enhance energy transfer pathways in Ca9Ga(PO4)7 phosphors. Under 331 nm excitation, dual emissions from Eu2+ (415 nm) and Cr3+ (696 nm) were achieved, with Zn2+ enhancing the near-infrared (NIR) of Cr3+. The optimal Cr3+ concentration led to an approximately six-fold increase in NIR emission intensity, attributed to Eu2+-induced crystal field modulation and efficient dipole-dipole energy transfer, which are evidenced by comparing the emission spectra and decay curve lifetimes. Temperature-dependent emission spectra revealed that Eu2+ emission remained stable, while Cr3+ emission exhibited significant temperature sensitivity in Ca9Ga(PO4)7:Zn2+,Eu2+, Cr3+, enabling precise temperature sensing with a peak sensitivity of 1.256 % K-1 at 298 K. This work offers a novel approach to improving energy transfer efficiency and dual-emission properties, contributing to the development of high-performance, real-time optical thermometry and photonic technologies.