Multifunctionalities of near-infrared upconversion luminescence, optical temperature sensing and long persistent luminescence in La3Ga5GeO14:Cr3+,Yb3+,Er3+ and their potential coupling

Abstract

The multifunctionalities of La₃Ga₅GeO₁₄:Cr³⁺,Yb³⁺,Er³⁺ (LGG:Cr³⁺,Yb³⁺,Er³⁺) with respective functions of near-infrared (NIR) upconversion (UC) luminescence, optical temperature sensing (OTS) and long persistent luminescence (LPL) were carried out and investigated in detail, which makes the materials attractive for bioapplications. The NIR UC luminescence at ∼830 nm with deep penetration in tissues is ascribed to the ⁴T₂ → ⁴A₂ transition of Cr³⁺. The OTS function based on the intensity ratio variation of ²H_11/2 → ⁴I_15/2 to ⁴S_3/2 → ⁴I_15/2 transitions of Er³⁺ ion detected that the thermal effects of the UC material caused by the laser irradiation ranges from 307 to 332 K for pumping power of 60 to 86 mW mm⁻². It also showed LPL of Cr³⁺ with a defect trap depth of ∼0.77 eV below the conduction band, benefiting excitation-free and noise-free imaging in tissues. Additionally, anomalous temperature dependant UC emission behaviours of Cr³⁺ and Er³⁺ in this material were also characterized and discussed, which can be understood by the configurational coordinate (CC) model and the complex forward and backward energy transfer processes among the dopants, respectively. The potential coupling of these functions was further discussed, such as UC induced NIR LPL, which would repetitively restrengthen the fading LPL signals and alert the operators to thermal damage of the biosystems by the NIR laser in the tissue imaging.