Lanthanide-doped upconversion nanomaterials are emerging as promising candidates in optoelectronics, volumetric display, anti-counterfeiting as well as biological imaging and therapy. Typical modulations of upconversion through chemical methods, such as controlling phase, composition, morphology and size enable us to rationally manipulate emission profiles and lifetimes of lanthanide ions by using continuous-wave laser excitation. Here we demonstrate that under pulsed laser excitation the emission color of NaYF4:Er/Tm (2/0.5%)@NaYF4 core-shell nanoparticles has an obvious transformation from green to red colors. Moreover, both pulse duration and repetition frequency are responsible for manipulating the upconversion emission color. The mechanism of the phenomena may be that the pulsed laser sequence triggers the emission levels to non-steady upconversion states first, and then cuts off the unfinished population process within the pulse duration. This pump source dependent and resultant tunable fluorescence emission enables NaYF4:Er/Tm (2/0.5%)@NaYF4 nanoparticles as a promising fluorophore in the transparent anti-fake printing.

Organolead halide perovskites (OHPs) have shown unprecedented potentials in optoelectronics. However, the inherent large bandgap has restrained its working wavelength within 280-800 nm, while light at other regions, e.g., near-infrared (NIR), may cause drastic thermal heating effect that goes against the duration of OHP devices, if not properly exploited. Herein, a solution processable and large-scale synthesis of multifunctional OHP composites containing lanthanide-doped upconversion nanoparticles (UCNPs) is reported. Upon NIR illumination, the upconverted photons from UCNPs at 520-550 nm can be efficiently absorbed by closely surrounded OHP nanowires (NWs) and photocurrent is subsequently generated. The narrow full width at half maximum of the absorption of rare earth ions (Yb 3+ and Er 3+ ) has ensured high-selective NIR response. Lifetime characterizations have suggested that Förster resonance energy transfer with an efficiency of 28.5% should be responsible for the direct energy transfer from UCNPs to OHP NWs. The fabricated proof-of-concept device has showcased perfect response to NIR light at 980 and 1532 nm, which has paved new avenues for applications of such composites in remote control, distance measurement, and stealth materials.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201801782. mobility, tunable direct bandgap, long electron-hole diffusion distance, as well as the merits of low-cost and earth-abundant, organolead halide perovskites (OHPs) with a general chemical formula of APbX 3 (A = organic ammonium cation, X = halide anion) have recently drawn unprecedented attention as a type of photoactive materials with competitive performance in the areas of optical, electronic, and optoelectronic devices. [1][2][3][4][5][6][7] A typical example is the exponentially increased studies on perovskite in solar energy conversion, the effort from which has pushed rapid and continuous improvement of the energy conversion efficiency from originally 3.8% to currently 22.1%, making it one of the most promising materials toward commercialization. [8][9][10][11][12] In addition, OHP has also shown extraordinary potentials in other areas ranging from light-emitting diodes (LEDs) to photodetectors, nonlinear optical devices, lasers, and X-ray sensors. [13][14][15][16][17][18][19][20] Unfortunately, as a typical light harvesting material with excellent performance, a common but intrinsic blemish of pure OHP at both bulk and the nanoscale is that it can only convert part of the UV-visible light (280-800 nm) in the standard AM1.5G sunlight spectrum (280-2500 nm) into electric signals due to the medium bandgap determined by both the chemical composition and crystal structure. [21][22][23] Thus, near-infrared (NIR) light that possesses ≈52% of the total solar irradiance may generate drastic thermal heating effect that shortens the duration of the relevant devices, while the solar energy conversion efficiency may be further increased if properly utilized...

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