Unveiling the uncommon blue-excitable broadband yellow emission from self-trapped excitons in a zero-dimensional hybrid tellurium-based double perovskite

Abstract

Low-dimensional metal halides with ns² lone-pair electrons have been recognized as new generation luminescent emitters for various optoelectronic applications. However, 5s² configuration tellurium halides have not received substantial attention despite their fascinating photoluminescence (PL) properties. Here, a hybrid tellurium-based double perovskite of (C₂₀H₂₀P)₂TeCl₆ is developed, in which the [TeCl₆]²⁻ octahedra are completely surrounded by [C₂₀H₂₀P]⁺ organic cations to form a unique zero-dimensional (0D) “host–guest” structure. An uncommon broadband yellow emission peaking at 570 nm with ultra-broad excitation from ultraviolet to blue light is excavated, which originates from the triplet self-trapped exciton (STE) emission of Te⁴⁺. Moreover, the 5s² electronic transition mechanism of Te⁴⁺ is systematically revealed in depth, benefiting from the temperature-dependent fluorescence dynamic analysis and auxiliary theoretical calculations. It is concluded that the distortion degree of the [TeCl₆]²⁻ octahedron comprehensively affects the full width at half-maximum (FWHM) (positive correlation), Stokes shift (negative correlation) and PL intensity (negative correlation) with increasing temperatures. This work sheds new light on the PL behaviour of Te⁴⁺ and opens up a feasible avenue for blue-excitable broadband emissions in low-dimensional organic–inorganic hybrid double perovskites.