“…The lifetime f of 4 I 13/2 determined by the single exponential fitting is around 7.20 ms, which is longer than the radiative time (see Table 5). This phenomenon has also existed in some other Er 3+ -doped hosts, such as Er 3+ :NaGd(WO 4 ) 2 [13], Er 3+ :NaY(MoO 4 ) 2 [14], and Er 3+ :LiLa(MoO 4 ) 2 [19]. There exist energy transfer between Er 3+ , the excited state absorption and serious self-absorption in Er 3+ :LiGd(MoO 4 ) 2 crystal; therefore, the rate of the depopulation from 4 I 13/2 decreases, accordingly, resulting in the increase of the measured lifetime of 4 I 13/2 [35,36].…”