Spectral engineering and thermometric performance of LiIn(Si2-xGex)O-6: Cr-3+ phosphor for multi-mode NIR thermometry

Exploring the phosphors with tunable NIR emission to realize versatile application is highly desired while remains a challenging. Herein, we show that the composition modification of Si/Ge ratio in LiIn(Si2-xGex)O-6: Cr-3+ could lead to a precise tuning of Cr-3+ emission wavelength in 840-900 nm range with significant emission enhancement. The spectral engineering is quantitatively analyzed on the base of structural variation and crystal fielding parameters, revealing that the PL tuning is originated from reducing crystal field by Ge4+-induced lattice expansion. It is found that the strong temperature-dependence of Cr-3+ emission enables it to read the temperature in three ways: variation of peak wavelength, fluorescence intensity and decay lifetime variation. All modes exhibit good linear response with R-2 > 0.99 in range of 293-473 K. The ability to absorb and emit in NIR-I biological window allows it to be used as a thermometer in deep tissue temperature sensing and imaging. All results indicate that this phosphor is of great potential in NIR thermometry application.