Toward tunable and bright deep-red persistent luminescence of Cr3+ in garnets

Garnet structure (A(3)B(2)C(3)O(12)) with three different cation sites is a very flexible host material widely used for w-LEDs, solid-state lasers, scintillators, and so on. In this work, we have successfully developed six different Cr3+-doped garnets: Y3Ga4.99Cr0.01O12 (YGG:Cr), Gd3Ga4.99Cr0.01O12 (GGG:Cr), Lu3Ga4.99Cr0.01O12 (LuGG:Cr), Y3Sc1.99Cr0.01Ga3O12 (YSGG:Cr), Gd3Sc1.99Cr0.01Ga3O12 (GSGG:Cr), and Lu3Sc1.99Cr0.01Ga3O12 (LuSGG:Cr), which exhibit persistent luminescence (PersL) due to Cr3+ emission matching well with both the response curve of the Si detector and the wavelength region of the first biological window (NIR-I, 650-950 nm). The main emission band of Cr3+ in these garnets can be easily tunable from the sharp R-line emission due to the E-2 ((2)G)(4)A(2) (F-4) transition in the strong crystal field to the broad band emission due to the T-4(2) (F-4)(4)A(2) (F-4) transition in the weak one when Lu3+ in the A site and Ga3+ in the B site are, respectively, replaced by larger cations, Y3+/Gd3+ and Sc3+. Furthermore, based on the knowledge of 4f energy levels of 15 lanthanide ions in the host-referred binding energy (HRBE) diagram, we took the GSGG host as a typical example to discuss the feasibility of four trivalent lanthanides (Sm3+, Eu3+, Tm3+, Yb3+) as potential sensitizers for enhancing Cr3+ PersL.