Red-to-ultraviolet light chargeable Sm2+-activated deep-red persistent phosphor for simultaneous bioimaging and bio-temperature sensing

Persistent phosphor-based bio-applications do not need real-time photo-excitation and do not suffer from disturbance of stray excitation light, auto-fluorescence of the measured substance and heat produced by excitation. However, the persistent phosphors that well match the optical biological windows are deficient. Here, we report for the first-time divalent samarium (Sm ²⁺) activated persistent phosphor with dual-functionality for simultaneous bioimaging and bio-temperature sensing. The persistent phosphor is Sm ²⁺ and Nd ³⁺codoped SrAl ₂Si ₂O ₈ that can be photo-charged in 250–660 nm and shows deep-red persistent luminescence (PersL) originated from both the 4 f ⁵5 d ¹ → 4 f ⁶ and ⁵D ₀ → ⁷F _J ( J = 0, 1, 2, 3, 4) transitions that well match the first optical biological window. The intense PersL output shows the effective operation temperature range of 240–340 K, covering the physiological temperature range of 298–325 K. It is found that quantum tunneling dominates both the visible light including red light charging process and PersL generating process. The temperature dependent PersL intensity ratio of the thermally coupled 4 f ⁵5 d ¹ → 4 f ⁶ emission band and the ⁵D ₀ → ⁷F _J emission lines is studied and a maximum relative sensitivity of 4.81 % K ⁻¹ at 200 K and 2.17–1.82 % K ⁻¹ in the physiological temperature range are achieved. The dual-functionality of SrAl ₂Si ₂O ₈:1 %Sm ²⁺,1 %Nd ³⁺ for simultaneous bioimaging and bio-temperature sensing is demonstrated. Our findings open up new scenarios for multifunctional applications of Sm ²⁺.