On the Er3+ NIR photoluminescence at 800 nm

Here, we study the Er 3+ NIR 4 I 9/2 - 4 I 15/2 photoluminescence peaking at 800 nm. It can be detected with a good signal-to-noise for the prepared CaWO 4 :Yb 3+ ,Er 3+ phosphors upon excitation at 980 nm. When directly exciting the Er 3+ green and red emitting states over the 333-773 K temperature range, the 800 nm photoluminescence for the samples is undetectable. It shows that the non-radiative relaxation from the upper excited states to the 4 I 9/2 emitting state is extremely inefficient. Moreover, the 800 nm photoluminescence decay curve is measured at high temperatures. It is found that the 800 nm emission always has a similar lifetime with the Er 3+ 4 I 11/2 - 4 I 15/2 ransition. This reminds us that the Er 3+ 4 I 9/2 state is mainly populated by the adjacent lower 4 I 11/2 state by a thermally coupled way.