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Perovskite quantum dots are considered to be one of the most promising materials for next-generation backlight displays due to their narrow emission width, high color purity and tunable luminescence. However, the deterioration and failure of perovskite quantum dots under stimulation from the external environment (e.g., light, heat, and humid air) limit their practical applications. Herein, CsPbBr3@glass with excellent stability and optical properties was successfully prepared by optimizing the quantum dot nucleation/growth conditions. The CsPbBr3@glass@PDMS hierarchical structure film with a full width at half maximum of ∼17 nm and photoluminescence quantum yield of ∼80% was obtained via the physical dilution method to eliminate the internal filtering effect. Benefiting from the dual protection of the inorganic glass network and PDMS polymer matrix, the film exhibited excellent water/heat resistance. As an application demonstration, a white LED backlit unit was designed by coupling a CsPbBr3@glass@PDMS green film and Mn4+:K2SiF6 red film with a home-made blue light guide panel, endowing the LCD with a wide color gamut (a color gamut of 159% for commercial LCD, 108% for NTSC, and 81% for Rec. 2020), confirming its great potential in the display industry. [ABSTRACT FROM AUTHOR]

The development of luminescent materials with concurrent tunable spectral profile and brightness is a great challenge to improve the security of the authentic items and shield against counterfeiting. Herein, we report the realization of in situ hexagonal-to-cubic phase transition of Yb/Er:NaLuF4 nanocrystals inside inorganic glass via simply modifying the heating (glass crystallization) temperature, leading to simultaneous control of upconversion emission color and intensity. Impressively, this peculiar phase transition process is reversible upon cyclic heating/cooling thermal-treatment and the accompanying repeatable upconversion emission behaviors are retained. It is experimentally demonstrated that multiple patterns visualized using screen-printing inks containing the investigated samples and the anti-counterfeiting prototypes are practically applicable by switching in situ glass crystallization temperatures. These findings show great promise of the designed lanthanide-doped NaLuF4@glass nanocomposites in high-level anticounterfeiting applications and give new insights for the development of advanced optical materials. [ABSTRACT FROM AUTHOR]

In situ nanocrystallization of homogeneously distributed Lu–Ln (Lu = La–Lu, Sc) solid-solution potassium lanthanide fluorides inside the same aluminosilicate glass matrix is reported. These precipitated nanocrystals exhibit Ln3+ radius dependent phase structures, i.e., cubic K(Lu/Ln)3F10 for large-radius Ln3+ ions and orthorhombic K(Lu/Ln)2F7 for small-radius Ln3+ ones. Particularly, a Lu–Yb system shows the ability to completely substitute between Lu and Yb in the K(Lu/Yb)2F7 nanocrystals, and Er (2 mol%):K(Lu0.5Yb0.5)2F7@glass yields the best upconversion quantum yield of 0.7%, which is far higher that the value of well-known Yb/Er (20/2 mol%):NaYF4@glass (0.13%). Taking Er/Tm:K(Lu0.5Yb0.5)2F7@glass as a color converter, a 980 nm laser-driven upconverted lighting device can be constructed to produce bright white-lighting with an optimal luminous efficiency of 0.53 lm W−1 and an energy efficiency of 1.31%. In addition, Er:KYb2F7@glass shows a significant photothermal effect owing to 100% Yb3+ host ions, leading to 980 nm laser-power-sensitive upconversion luminescence colors. As a proof-of-concept experiment, a specially designed Er:KYb2F7@glass-based flower pattern with tunable upconversion colors is adopted to demonstrate its practical application in high-end anti-counterfeiting. [ABSTRACT FROM AUTHOR]

This work demonstrates a novel mechanism of temperature sensitive upconversion luminescence. The Yb/Er:La2MoO6 phosphor is taken as a typical example. The laminated lattice structure of the La2MoO6 host endows a high potential of the 4F7/2 + 4I11/2→4F9/2 + 4F9/2 cross relaxation of the Er3+ dopant. It is found that such cross relaxation is sensitive to the variation of temperature, resulting in a distinct variation in fluorescence intensity ratio and thus a remarkable thermochromic upconversion luminescence. Employing this material as an optical thermometer, the maximum relative sensitivity is calculated to be 1.6% K−1 at room temperature, which is superior to most of the Er based thermometers reported previously. In addition, when an impulse pump is utilized, the maximum sensitivity can be further enhanced up to 3.3% K−1. The anisotropic thermal expansion of the La2MoO6 host lattice is proposed to be responsible for such temperature dependent luminescence. Other hosts (i.e. LaOCl and BiOCl) with similar laminated lattice structures have also been investigated, which exhibit a similar temperature sensing property. This work not only presents a novel strategy for constructing upconversion thermometric materials, but also provides inspiration that developing impulse excited optical thermometric materials might be a promising route for the field of temperature sensing. [ABSTRACT FROM AUTHOR]