Luminescence blinking in Eu3+ doped yttrium oxysulfide (Y2O2S:Eu3+) quantum-dot ensembles: Photo-assisted relaxation of surface state(s)

Ensembles of Y2O2S:Eu3+ widegap semiconductor nano-crystals exhibit ON-OFF fluorescence blinking phenomenon, which mimic II-VI semiconductor quantum-structures. Attempt has been made to explain this phenomenon under the ambit of diffusion controlled electron transfer (DCET) model. Insights derived using opto-impedance technique in conjunction with the DCET model clearly establish the relaxation of surface state(s) through a diffusion process. Ensembles of Y2O3:Eu3+ nano-crystals, the insulating counterpart investigated for comparison does not show such fluorescence blinking.

(a) Photograph images of successive frames showing ON-OFF blinking in Y2O2S:Eu3+ nano-crystals, (b) corresponding fluorescence intensity versus time plot. (c) histogram showing the PL intensity versus number of ON-OFF occurrences fitted under single Gaussian. Using PL intensity scales 'ON' and 'OFF' states are identified as marked. Also (d) opto-impedance data corresponding to Warburg impedance part (diffusion process) on Y2O2S:Eu3+ nano-crystals showing variation in slope (m) upon UV shining in a comparable time scale as the blinking is indicated.