The carbon-dots/NaLuF 4 microcrystals have been synthesized by the hydrothermal method and bright blue emission from carbon dots is observed in aqueous and solid state under 365 nm excitation. Self-quenching property of the carbon-dots/NaLuF 4 microcrystals under solid state was deeply investigated, by changing the ratio of citric acid (CA) and ethylenediamine (DHE). The results indicate that the carbon dots can be effectively adsorbed and dispersed on the surface of NaLuF 4 microcrystals, suppressing the aggregation of carbon dots. Furthermore, the upconversion luminescence can also be realized under 980 nm laser excitation. From the above observations, the carbon-dots/NaLuF 4 microcrystals not only reveal emission property of carbon dots and NaLuF 4 , respectively, but also optimize the property of carbon dots. It provides a promising new strategy to prevent the carbon dots quenching in solid state and the carbon-dots/NaLuF 4 microcrystals may have potential multi-applications in different fields including temperature sensing, solid-state display lighting as well as security inks.
Internal OH– defects always cause significant depletion of excitation energy for low upconversion efficiency; however, preventing the incorporation of OH– into the crystal lattice is very difficult during the synthesis of upconversion crystals. In this work, red upconversion emission is dramatically enhanced in Er3+-sensitized hexagonal NaLuF4 (β-NaLuF4) microcrystals through a collaborative effect of ion exchange and Tm3+ doping. The ion exchange can not only maintain the morphology very well but also strongly reduce the internal OH– defects, which can enhance the upconversion luminescence due to improved excitation energy harvesting and red to green (R/G) ratio due to intense cross-relaxation. Doping of Tm3+ as an energy trapping center not only regulates the red emission output but also reduces the excitation energy loss. β-NaLuF4:Er,Tm microcrystals after ion exchange exhibit stronger red upconversion emission compared with β-NaYF4:Er,Tm and β-NaGdF4:Er,Tm counterparts. Moreover, fluorescent labeling of the fingerprint pattern printed from β-NaLuF4:Er,Tm microcrystals with stable and intense red fluorescence has been demonstrated under 980 nm excitation.
In this work, monodisperse β-NaLuF 4 :Yb,Er microcrystals with intense upconversion emission were synthesized via a modified hydrothermal method . With the increase of reactant concentration, their production yield is increased obviously, and the upconversion emission intensity in β-NaLuF 4 :Yb,Er microcrystals is also enhanced significantly. The luminescence enhancement should be attributed to minimal internal OH − defects, validated by a combination of analytical X-ray diffraction (XRD), energy dispersive spectrum (EDS), and Eu 3+ structural probe measurements. We also reveal that high Na + :RE 3+ ratio in the β-NaLuF 4 :Yb,Er microcrystals prepared under Na + -rich reaction will arouse the increased repulsive energy of β-NaLuF 4 microcrystals between F − and OH − anions and then facilitate the substitution of large OH − ions by small F − ions under F − -rich reaction conditions. Minimal OH − concentrations can limit nonradiative relaxation and promote excitation energy harvesting for high upconversion efficiency. The presented results not only offer a facile method for the simultaneous production yield and luminescence intensity increase of β-NaREF 4 microcrystals, but also uncover a better insight into the upconversion emission alterations, which is favorable to broaden their practical applications.
危险品化学品经营许可证（带存储）