Deciphering the near-infrared emission capabilities of chromium substituted BaLaLiTeO6 double perovskites

Abstract

The enormous capability of near-infrared (NIR) spectroscopy heightens the demand for the development of broadband NIR phosphors. Chromium incorporated tellurate double perovskite compounds are seldom explored and could be a prospective choice for broadband NIR phosphors. The present work deals with the synthesis and the prospective NIR luminescence characteristics of a series of BaLaLiTe_1-xCr_xO₆ (x = 0, 0.004, 0.008, 0.01, 0.02, 0.04 and 0.06) double perovskite phosphors synthesized via solid-state reaction route for the first time. X-ray diffraction, Raman and FTIR spectroscopy analyses were employed to draw inferences about the structural modifications induced by the substitution of Cr³⁺ ions in BaLaLiTeO₆. The confirmation of valence states of all the ions by XPS analysis, optical characteristics by diffuse reflectance and photoluminescence spectroscopy were carried out in detail. The NIR luminescence of BaLaLiTeO₆ centered at 972 nm under 328 nm excitation is particularly striking and is attributed to the simultaneous existence of oxygen vacancies, Te⁴⁺ and Te⁶⁺ ions in the phosphor. The excitation spectra of BaLaLiTe_1-xCr_xO₆ monitored at 954 nm present excitation bands corresponding to host excitation, ⁴A₂(⁴F)→⁴T₁(⁴P), ⁴A₂(⁴F)→⁴T₁(⁴F) and ⁴A₂(⁴F)→⁴T₂(⁴F) transitions of Cr³⁺ ions. The photoluminescence emission spectra exhibited a broadband NIR emission with a FWHM of 168 nm by 270 nm excitation. BaLaLiTe_0.99Cr_0.01O₆ phosphor exhibited the highest emission intensity. The exact energy transfer mechanism and crystal field parameters of the synthesized phosphors were also explored in detail. This work attempts to probe into the possibility of tellurate-based double perovskite as NIR phosphor for NIR pc-LEDs and in diverse photonic fields.