Channelling Er3+-activated vanadate garnet's multimode luminescence for high-sensitivity optical thermometers and NIR-II pc-LEDs for bioimaging

Abstract

Channeling the dual-mode luminescence of an Er³⁺-activated Sr₂NaMg₂V₃O₁₂ garnet is required for meeting the demands of multifunctional phosphors for optical thermometry and bioimaging. Herein, the temperature-sensing properties and prospects of bioimaging of the vanadate garnet, exhibiting dual-mode photoluminescence, are investigated in detail. The negative thermal quenching of the G₁ band via phonon-assisted population inversion resulted in a distinct thermal response. Based on the fluorescence intensity ratio, FIR, and Raman-PL intensity ratio, the RPIR method, a maximum relative temperature sensitivity of 8.9% K⁻¹ at 80 K, is observed, offering wide range thermometry. Tunability of emission from the visible to NIR-II region with maxima at 1536 nm is achieved. Notably, benefitting from the enhanced structural rigidity of the garnet followed by the higher Debye temperature, the phosphor exhibits excellent thermal stability with T_1/2 > 500 K. The fabricated NIR-II pc-LEDs exhibit stable NIR-II emission even at higher input bias currents. Furthermore, the prospects of fabricated NIR-II pc-LEDs for bioimaging are evaluated, confirming the potentiality of the present phosphor for risk-free imaging of biological systems. This work puts forth a new dimension to the vanadate garnets for realizing optical thermometers with the highest sensitivity and risk-free imaging of biological systems.