Research Of Near-infrared Luminescence And Photon Energy Upconversion Of Copper Silicates

BaCuSi4O10 (Han blue) and CaCuSi4O10 (Egyptian blue) are pigments found in ancient articrafts all over the world. Besides their brilliant blue color, stable physical and chemical properties, we found the have both strong Stokes effect and Anti-Stokes effect at the same time. Therefore, they could be used as efficient photonic materials.Under excitation of 440-800 nm visible light, their Cu2+, as luminescent center, can emit broad peak centered at around 930 nm. We have investigated the luminescent mechanism. By comparing luminescent of CaCuSi4O10, SrCuSi4O10 and BaCuSi4O10, we studied the influence of ligand field environment to Cu2+ luminescent center. With coordination ions switch from Ca2+â†'S42+â†'Ba2*, the emission peak of these copper silicates experiences a redshift, which is a result of both lattice expansion and Jahn-Teller effect, and is consistent with Crystal Field Theory.Near-infrared luminescence of Cu2+ can also be produced by pumping using NIR laser diodes. With the rise of pumping density, the emission bandwidth increases notably and stretches to the visible region, giving rise to bright, and broadband photon upconversion (UC). The emission peak by PL does not change with the increase in the excitation laser energy. In comparison, the peak of thermal radiation driven by laser excitation is expected to experience blue shift with the increase of laser power, according to the law of blackbody radiation. Practically both processes could occur under laser excitation, and thus the two mechanisms are not easily distinguishable from the emission spectra. Since the emission spectra can be successfully fitted by the law of black body radiation, it is reasonable to suggest that laser driven thermal radiation may be dominating, especially under high powder laser excitation. At high pumping densities, the 3d levels of Cu2+ would become saturated, therefore enabling the promotion of electrons further to the conduction band. This multiphoton process associate with a photon avalanche mechanism was supported by the photocurrent measurement for several RE3+ doped compounds and the white emission has been ascribed to a charge transfer process.