Enhanced VIS-NIR emission of Re4+ doped Cs2ZrCl6 for optical thermometry and near-infrared illumination applications†

Abstract

The luminescence properties of transition metal d³ ions have exhibited widespread application potential in optical thermometry, while the emissive characteristics of self-trapped excitons in lead-free metal halides have garnered significant attention in the field of optoelectronics. Nonetheless, a comprehensive investigation into the temperature-dependent luminescence features of d³ ion-doped lead-free metal halides remains an area demanding in-depth exploration. Herein, we report on the visible and near-infrared (NIR) photoluminescence of 5d³ Re⁴⁺ doped vacancy-ordered metal halide Cs₂ZrCl₆ synthesized via hydrothermal methods. The undoped Cs₂ZrCl₆ host exhibits broad band self-trapped exciton (STE) emission. PL measurements reveal that its anti-thermal quenching PL under 270 nm excitation is predominantly due to the enhancement of the hot absorption band tail. Upon UV excitation, Re⁴⁺ doped Cs₂ZrCl₆ concurrently emits STE emission and features a narrow-band NIR emission at 730 nm with vibronic sideband details from the ReCl₆²⁻ octahedra, alongside a narrow-band emission at 1340 nm. By harnessing the luminescence intensity ratio (LIR) technique, combined with the anti-thermal quenching of STEs and the thermal quenching of Re⁴⁺ emission, optical thermometry with a relative sensitivity as high as 2.76% K⁻¹ is achieved. Our findings suggest that Re⁴⁺-doped Cs₂ZrCl₆ represents a multifunctional optoelectronic platform with promising applications in NIR illumination and temperature sensing.