Abstract
The Er3+ ion’s 4F7/2-4I15/2 transition, which has been less reported in the past, is studied in CaWO4:Yb3+/Er3+ phosphors. It has been confirmed that this transition is from the two-photon upconversion mechanism when the 980 nm laser diode is used as the excitation source. Moreover, the transition has the same lifetime with the neighboring lower 2H11/2/4S3/2 states, suggesting that the 4F7/2/4S3/2 states are thermally linked. It is shown that the 4F7/2/4S3/2-4I15/2 emissions can be used for ratiometric temperature measurement. Their relative thermal sensitivity is up to 2820/T2, one of the largest sensitivities reported so far. It is very close to the theoretical maximum 2877/T2.
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