Abstract
We report that the rare-earth (RE) ion, Sm-doped ZnO, acts as white light emitting vacuum ultraviolet (VUV) phosphors and possesses an ultrahigh color rendering index (CRI) and color quality scale (CQS). The VUV-excited emission spectra measured from the synchrotron source reveal the emergence of multi-color emission bands in the visible-IR region and substantially depend on the concentration of ${{\rm Sm}^{3 +}}$ ions. A mechanism is proposed to elucidate the origin behind the high-energy bandgap excitation of the host charge carrier and subsequent energy transfer to the ${{\rm Sm}^{3 +}}$ states leading to additional green-yellow-orange emission bands of ${{\rm Sm}^{3 +}}{(^4}{{\rm G}_{5/2}}{\to ^6}{{\rm H}_{\rm J}}\;({\rm J} = {5/2},\;{7/2},\;{\rm and}\;{9/2}))$. High-quality cool white light (correlated color temperature 5600 K) having CIE coordinates (0.33, 0.35) with a CRI as high as 95.89 and a CQS value of 94.49 is achieved for ${{\rm Zn}_{0.985}}{{\rm Sm}_{0.015}}{\rm O}$ under synchrotron VUV radiations. This Letter demonstrates that RE activated ZnO-based phosphors are expected to be a promising candidate in solid state lighting, as well as plasma display devices.
© 2020 Optical Society of America
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