Demonstration of Temperature Dependent Energy Migration in Dual-Mode YVO(4): Ho(3+)/Yb(3+) Nanocrystals for Low Temperature Thermometry

A dual mode rare-earth based vanadate material (YVO(4): Ho(3+)/Yb(3+)), prepared through ethylene glycol assisted hydrothermal method, demonstrating both downconversion and upconversion, along with systematic investigation of the luminescence spectroscopy within 12–300 K is presented herein. The energy transfer processes have been explored via steady-state and time-resolved spectroscopic measurements and explained in terms of rate equation description and temporal evolution below room temperature. The maximum time for energy migration from host to rare earth (Ho(3+)) increases (0.157 μs to 0.514 μs) with the material’s temperature decreasing from 300 K to 12 K. The mechanism responsible for variation of the transients’ character is discussed through thermalization and non-radiative transitions in the system. More significantly, the temperature of the nanocrystals was determined using not only the thermally equilibrated radiative intra-4f transitions of Ho(3+) but also the decay time and rise time of vanadate and Ho(3+) energy levels. Our studies show that the material is highly suitable for temperature sensing below room temperature. The maximum relative sensor sensitivity using the rise time of Ho(3+) energy level ((5)F(4)/(5)S(2)) is 1.35% K(−1), which is the highest among the known sensitivities for luminescence based thermal probes.