Enhancing the inherent NIR photoluminescence in SrLaLiTeO through Cr-Yb co-substitution for high performance pc-LEDs.

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 SrLaLiTeO double perovskite centered at 970 nm under 340 nm excitation is particularly intriguing. This phenomenon is attributed to the photoluminescence of Te ions. This study also examines the NIR luminescence of Cr-Yb co-doped SrLaLiTeO. The host and SrLaLiTeO:3%Cr, %Yb ( = 1, 2, 4, 6, 8, 10 mol%) were synthesized using the solid-state ceramic route. The successful incorporation of Cr and Yb ions into the host lattice was confirmed through XRD, Raman, and diffuse reflectance spectral analyses. Under 270 nm excitation, the photoluminescence (PL) of SrLaLiTeO:Cr exhibits a blueshift of the PL band to 965 nm due to the T(4F) → A(4F) emission component of Cr ions. The excited-state lifetime of SrLaLiTeO:0.5%Cr was measured at 36 μs, but this decreased to 26 μs as the Cr concentration reached 10 mol%, primarily due to the enhancement of non-radiative energy transfer between Cr ions. Incorporating Yb 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 F → F transitions of Yb ions, indicating an efficient energy transfer from Cr to Yb. Furthermore, the study also reveals that Yb emission is observed even without Cr ions in SrLaLiTeO under 340 nm excitation, suggesting the possibility of energy transfer from the host to Yb 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 SrLaLiTeO, SrLaLiTeO:3% Cr, and SrLaLiTeO:3% Cr, 1%Yb.