Multi‐Color Luminescence Transition of Upconversion Nanocrystals via Crystal Phase Control with SiO₂ for High Temperature Thermal Labels

Abstract

Upconversion nanocrystals (UCNs)‐embedded microarchitectures with luminescence color transition capability and enhanced luminescence intensity under extreme conditions are suitable for developing a robust labeling system in a high‐temperature thermal industrial process. However, most UCNs based labeling systems are limited by the loss of luminescence owing to the destruction of the crystalline phase or by a predetermined luminescence color without color transition capability. Herein, an unusual crystal phase transition of UCNs to a hexagonal apatite phase in the presence of SiO2 nanoparticles is reported with the enhancements of 130‐fold green luminescence and 52‐fold luminance as compared to that of the SiO2‐free counterpart. By rationally combining this strategy with an additive color mixing method using a mask‐less flow lithography technique, single to multiple luminescence color transition, scalable labeling systems with hidden letters‐, and multi‐luminescence colored microparticles are demonstrated for a UCNs luminescence color change‐based high temperature labeling system.

Thermal enhancement of upconversion emission in nanocrystals: a comprehensive summary

“…Baek and co-workers developed a maskless flow lithography technique dispersing Ln 3+ -doped NaYF4 UCNPs and SiO2 NPs in a photocurable resin (polyurethane acrylate). 69 (Fig. 7e-g) The polymer solution was flown into a polydimethylsiloxane (PDMS) microfluidic channel and polymerized with patterned UV light.…”

“…(e) Temperature-sensitive luminescence colour hidden microparticles, (f) hidden pattern-and (g) hidden letterbased labelling system. Reproduced from ref 69. with permission from the Wiley-VCH.…”

Dual-modal Light-harvesting Microfluidic System via Simultaneous Up- and Down-Conversions for Enhanced Flow Photocatalysis

“…The unique up-converting luminescence characteristics of UCNs have been studied in various elds, including photovoltaics, encoding, bioimaging, and drug delivery. [22][23][24][25][26][27][28][29] Upon exposure to 980-nm NIR light, the synthesized UCNs showed luminescence at 530 and 660 nm, which overlaps with the absorption spectra of RB in the wavelength range 520-550 nm. The UCNs were capped with oleic acid (OA), which has a long hydrocarbon chain, to form a well-dispersed mixture in the hydrophobic AHPCS/TAPS matrix.…”

“…In these contexts, the anti-Stokes-shift luminescence phenomenon of upconverting nanocrystals (UCNs) has gained attention because it enables a dual-modal light-harvesting approach using both up-and down-converters to harness UV and near-infrared (NIR) light by expanding the wavelength range of electromagnetic radiation used to activate the photocatalyst. 16,17 In addition, NIR light generally exhibits deep light penetration in physical media. Therefore, using a matrix consisting of UCNs is a promising approach toward the construction of an effective light harvester.…”

Polarized upconversion luminescence from a single LiLuF4:Yb3+/Er3+ microcrystal for orientation tracking

“…In contrast to anisotropic emitters such as semiconductor nanowires, quantum rods, and nanoplates that exhibit size-and shape-dependent polarized luminescence [11][12][13][14], Ln 3+ -doped UCPs show distinguished nature of emission polarization which is independent of the particle size and morphology [15][16][17][18][19]. The upconversion luminescence (UCL) of Ln 3+ in a crystalline host matrix consists of many sharp emission peaks due to the multiple transition levels within the 4f N configuration and their crystal-field (CF) splitting into degenerate sublevels [20][21][22][23][24][25][26][27][28][29][30]. Each CF sublevel emission is polarized along a particular direction allowed by the crystallographic symmetry [31][32][33][34].…”