Preparation Of Single Red Band Upconversion Nanomaterials And Further Luminescence Enhancement

In recent years, lanthanide-doped nanocrystals have attracted a great deal of attention owing to their unique upconversion?UC? luminescence properties and broad potential applications in solid-state lasers, solar cell, optical-fiber-based telecommunications, lamps for illumination, flat-panel displays, optical storage and biological imaging. Compared to organic fluorophores and semiconducting nanocrystals, and quantum dots fluorophores, upconversion nanocrystals offer high photochemical stability, sharp emission bandwidths, and large anti-Stokes shifts?up to 500 nm? that separate discrete emission peaks from the infrared excitation. Along with the remarkable light penetration depth and the absence of autofluorescence in biological specimens under infrared excitation, these upconversion nanocrystals are ideal for use as luminescent probes in biological labelling and imaging technology.As we all known, the red region?600-700 nm? and near-infrared?NIR? spectral range?700-1000 nm? are generally addressed as the “optical window” of the biological tissues, due to the lack of the efficient endogenous absorbers. Moreover, the high energy photons with short wavelength?<600 nm? will promote biological autofluorescence. Therefore, in order to further improve the UC luminescence performance, we do some work and investigate to optimize the UC fluorescence in some popular cubic fluoride crystals NaYF₄, KZnF₃, KMnF₃.Presently, for UC nano materials, the most common approach to gain stable UC luminescence is based on the co-doping with Yb³⁺/Er³⁺, Yb³⁺/Tm³⁺, Yb³⁺/Ho³⁺. And the effective emission band of ogni combination are centred at 550 nm, 475 nm, and 545 nm. Apparently, all of these fluorescence will be absorbed by the biological tissue and cause the happen of biological autofluorescence. As a result, when these UC nano phosphors are used in biological imaging, the signal-to-noise ratio is low. In order to eliminate the fluorescence drawback of the lanthanide-doped UC nanocrystals in biological application. we introduce transition metal Mn²⁺ ios to tune the UC emission spectrum into the “optical window” region.In this paper, we mainly introduce four parts work. The first part is focusing on the UC luminescence and the UC energy transfer mechanism variation in the case of introducing different amount Mn²⁺ into NaYF₄:Yb³⁺/Er³⁺; the second part is devoted to investigate the synthesis and the luminescence enhancement of ? doping core/shell/shell structure, in this work, we do the theoretical analysis and experimental measurement to verify the UC efficiency of this structure is higher than the traditional core/shell structure; in the third part, we do the study of the Mn²⁺ ions' influence on the growth and UC luminescence of the KZnF₃:Yb³⁺/Er³⁺ nanocrystals; and in the last fourth part, Mg²⁺ doping KMn F₃:Yb³⁺/Er³⁺ nanoparticals are synthesized, and the single red band upconversion fluorescence enhancement is investigated as well.Our results show that the Mn²⁺ can really tune the UC emission of Yb³⁺/Er³⁺ from green to red, and in “optical window” region, a strong upconversion process from near-infrared to single red can happen indeed in low phonon energy cubic fluoride crystals by tri-doping Yb³⁺/Er³⁺/Mn²⁺. In addition, we also demonstrate the ? doping core/shell/shell structure have higher UC luminescence efficiency than that of the NaYF₄:Yb³⁺/Er³⁺/Mn²⁺ and the NaYF₄:Yb³⁺/Er³⁺/Mn²⁺@NaYF₄ structure. Last but not the least, when the 30%Mg²⁺ ions are introducing into KMnF₃:Yb³⁺/Er³⁺, the single band red UC emission intensity increase twenty times than that of no Mg²⁺ doped ones. Besides the excellent optical performance, all of our samples show another outstanding performance in particlas size and homogeneity. And all these property will impact on the field of bioimaging and labling based on UC nanoprobes.