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

Abstract

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.