Optical thermometry in low temperature through manipulating the energy transfer from WO66− to Ho3+ in Y2WO6:Ho3+ phosphors

Optical thermometry based on the adjacent thermally coupled levels of rare earth ions has been widely studied in the high temperature range, and shows unobvious effect at low temperature range. In this work, we propose a new method to achieve optical thermometry in 10˜300 K range through manipulating the energy transfer from WO66− to Ho3+. A comprehensive five-level rate-equation model is developed to establish the relation between lifetime ratios and temperature. It is found that the lifetime ratios of 540 nm (Ho3+) and 471 nm (WO66−) emissions are dependent on the phonon energy of Y2WO6 host and temperature. The values of sensor sensitivity reach the maximum 2.1% K−1 at 211 K in 30%Ho3+ doped Y2WO6, which is higher than the maximum of the reported phosphors at low temperature. It overcomes the shortcoming of unobvious thermal population of thermally coupled levels in low temperature range through traditional Boltzmann distributing method.