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[摘要]：Site-selective spectroscopy in hexagonal beta-NaYF(4):Er(3+),Yb(3+) has revealed different environments for Er(3+) ions (multisite formation). The low-temperature (4)S(3/2) -> (4)I(15/2)Er(3+) green emission depends on the excitation wavelength associated with the (4)F(7/2) Er(3+) level. We have studied the effect of hydrostatic pressure on the green, red, and blue Er(3+) emission upon NIR excitation at similar to 980 nm, in order to establish the role played by energy resonance conditions and the multiple Er(3+) sites due to the disordered structure for the upconversion (UC) process (energy tuning). The variation of photoluminescence spectra and lifetimes as a function of pressure and temperature reveals that the origin of the high green UC efficiency of the beta-NaYF(4):Er(3+),Yb(3+) compound is mainly due to the multisite distribution, and the low phonon energy of the host lattice. |
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