Abstract
Quaternary wide-band-gap oxychalcogenides (MZnOS, M = Ca, Sr, and Ba) are underexplored inorganic semiconductors compared with pure chalcogenides or oxides, in which more dopants could be simultaneously coordinated by oxide and chalcogenide anions. In this kind of materials, color-tunable photoluminescence (PL) could well be obtained without destructing structure. Due to the need of complex conditions for synthesis compared with Ca(Sr)ZnOS, the unique structure of BaZnOS remains largely unexplored as host for application in lighting/display fields. Spectroscopic measuring combined with XPS and DFT computational studies on pristine BaZnOS reveal that the weak multi-colored self-PL were originated from the intrinsic trap states of oxygen vacancies (VO2+, VO+ and VO0). The crystallographic occupancies of dopants Bi3+/Eu3+ and Li + at Ba2+ and Zn2+ sites, respectively were proved based on the Rietveld refinements and crystal chemistry rules. Tunable and thermally stable PL in the regions of cyan, white and even yellow could be systematically obtained from the BaZnOS: Bi/Eu via changing concentrations of dopants with the help of energy transfer (ET) from the host to dopants as well as Bi to Eu. The effect of unlit Li+ is acting both as charge balancer and fluxing agent for reducing calcination temperature and improving PL efficiency. Finally, as a proof-of-concept experiment, the BaZnOS: Bi/Eu/Li phosphor converted white light emitting diode (pc-wLED) was fabricated and produced attractive performances including high CRI of 82.5, low CCT of 4024 K, CIE coordinates of (0.3462, 0.3531), and luminous efficiency (LE) of 16.5 lm/W. Altogether, the stable Bi/Eu/Li tridoped BaZnOS phosphor is a promising candidate to be applied in lighting/display fields.
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