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The development of blue/green/red tricolor upconversion (UC) phosphors under invisible light irradiation has attracted significant interest in emerging applications such as anti‐counterfeiting, three‐dimensional (3D) optical data storage, and solid‐state 3D displays. In this study, a series of LiYO2:RE3+,Yb3+ (RE = Tm, Ho, Eu) phosphors are successfully prepared via first precipitation process followed by calcination, and completely optimized for efficient tricolor UC luminescence with 980 nm laser excitation. Mechanisms involving two‐ or three‐photon absorption processes and low‐phonon‐energy‐suppressed multi‐phonon relaxation have been proposed for Ho3+(Eu3+)/Yb3+ and Tm3+/Yb3+ codoping, respectively. In addition, the RE3+ (Yb3+) concentration‐induced phase transition of the LiYO2 host is discussed for interesting possibilities in spectral regulation. Based on the broad color gamut achieved by the tricolor UC phosphor mixture, homochromatic and polychromatic metamerisms are experimentally fabricated via screen printing for high‐level anti‐counterfeiting and information security. Moreover, for a proof‐of‐concept demonstration, prototypes of 3D optical data storage and volumetric displays are constructed by embedding tricolor UC mixtures and their 3D printed patterns in polydimethylsiloxane. It is believed that the continuous exploration of tricolor UC under invisible light excitation for metamerism anti‐counterfeiting and 3D displays can promote the development of high‐level information security and advanced volumetric display technologies. [ABSTRACT FROM AUTHOR]

Tristimulus values and chromaticities, which are derived using the color matching functions (CMFs), are commonly used for color characterization, calibration, and specifications, with the stimuli having the same values believed to have the same color appearance (i.e., metameric match). Many studies, however, found that the stimuli having the same tristimulus values do not appear the same (known as metameric failure) due to the failure of CMFs in accurately characterizing the color matching mechanisms. Most past work investigated the performance of different CMFs through color matching experiments, with a smaller chromaticity or calculated color difference between the reference and test stimuli suggesting a better performance. Such differences, however, may not accurately characterize the performance of the CMFs, since the color spaces or chromaticity diagrams may not be uniform, in terms of the threshold of noticeable color difference. In this study, the human observers evaluated the perceived color difference between pairs of stimuli, which were calibrated to have the same tristimulus values calculated using the CIE 1931 2° CMFs, with two sizes of field of view (FOV). The results clearly suggested that the stimuli having the same tristimulus values may not always appear the same, which depended on the primaries and the FOV. More importantly, the results clearly suggested that the chromaticity differences from color matching experiments may overestimate the metameric failure, especially when the color differences were small. [ABSTRACT FROM AUTHOR]

PURPOSE. To evaluate the metameric disparities among monolithic zirconia materials with differing yttrium compositions across various lighting conditions. MATERIALS AND METHODS. Thirty-six square-shaped zirconia samples measuring 10 × 10 × 0.5 mm were prepared from monolithic zirconia materials with three different yttrium contents. A 0.2 mm thick layer of polymerized dualpolymerizable self-adhesive resin cement was created using a silicone mold with the same dimensions as the prepared zirconia specimens. To evaluate metamerism, color measurements were conducted using a spectrophotometer device on a neutral gray background in a color measurement cabinet that offers four different illumination environments. All samples underwent aging by subjecting them to 10000 thermal cycles using a thermal cycle tester. Following thermal aging, color measurements were taken once more, and the data were recorded using the CIE L*, a*, b* color system. Two-way ANOVA and Post-hoc Bonferroni tests were employed to analyze the data. RESULTS. It was observed that there was no statistical difference among the color measurements made in different illumination environments of the monolithic zirconia ceramics used to evaluate metamerism (P > .05). This observation remained consistent both before and after thermal aging. After thermal aging, the color of monolithic zirconia materials exhibited a tendency towards red and yellow hues, accompanied by a decrease in brightness levels. CONCLUSION. It can be stated that different illumination conditions did not affect the metamerism of monolithic zirconia materials, but there was a color change in monolithic zirconia materials after a thermal aging period equivalent to one year. [ABSTRACT FROM AUTHOR]