Enhancing the inherent NIR photoluminescence in SrLaLiTeO6 through Cr3+–Yb3+ co-substitution for high performance pc-LEDs

Abstract

Until now, double perovskite tellurates have not been reported to exhibit inherent NIR photoluminescence. Therefore, the current study's revelation of inherent NIR luminescence in SrLaLiTeO₆ double perovskite centered at 970 nm under 340 nm excitation is particularly intriguing. This phenomenon is attributed to the photoluminescence of Te⁴⁺ ions. This study also examines the NIR luminescence of Cr³⁺–Yb³⁺ co-doped SrLaLiTeO₆. The host and SrLaLiTeO₆:3%Cr³⁺, y%Yb³⁺ (y = 1, 2, 4, 6, 8, 10 mol%) were synthesized using the solid-state ceramic route. The successful incorporation of Cr³⁺ and Yb³⁺ ions into the host lattice was confirmed through XRD, Raman, and diffuse reflectance spectral analyses. Under 270 nm excitation, the photoluminescence (PL) of SrLaLiTeO₆:Cr³⁺ exhibits a blueshift of the PL band to 965 nm due to the ⁴T₂(4F) → ⁴A_2g(4F) emission component of Cr³⁺ ions. The excited-state lifetime of SrLaLiTeO₆:0.5%Cr³⁺ was measured at 36 μs, but this decreased to 26 μs as the Cr³⁺ concentration reached 10 mol%, primarily due to the enhancement of non-radiative energy transfer between Cr³⁺ ions. Incorporating Yb³⁺ into the system results in additional spectral lines with an enhanced intensity in the range of 970 nm to 1125 nm when excited at 270 nm. These emission lines correspond to the ²F_5/2 → ²F_7/2 transitions of Yb³⁺ ions, indicating an efficient energy transfer from Cr³⁺ to Yb³⁺. Furthermore, the study also reveals that Yb³⁺ emission is observed even without Cr³⁺ ions in SrLaLiTeO₆ under 340 nm excitation, suggesting the possibility of energy transfer from the host to Yb³⁺ ions. The thermal stability and crystal field parameters of the synthesized phosphors are also explained in detail. To explore the potential of these phosphors in practical applications, phosphor-converted NIR LEDs were fabricated using SrLaLiTeO₆, SrLaLiTeO₆:3% Cr³⁺, and SrLaLiTeO₆:3% Cr³⁺, 1%Yb³⁺.