Excitation-dependent multi-color emissions in Yb/Er/Eu: Gd2Ti2O7 pyrochlore for anti-counterfeiting

New near‐infrared emissions and energy transfer in Er3+‐doped MgAl layered double hydroxides

“…Compared with the 650 nm emission, the decay curves for the 720 and 850 nm emissions decreased sharply, especially for the 850 nm emission. Furthermore, lifetimes of 720 and 850 nm emissions were much shorter than those of either the present 650 nm emission or previous emissions [ 27,33,34,42,57,60,66 ] (seen in Table 4). As Er 3+ emissions strongly depend on the host, the decay of Er 3+ emissions may be different when Er 3+ ions are doped into different hosts.…”

“…In general, downconversion emissions for Er 3+ produce green ( 2 H 11/2 → 4 I 15/2 , 4 S 3/2 → 4 I 15/2 ) and red emissions ( 4 F 9/2 → 4 I 15/2 , 4 I 9/2 → 4 I 15/2 ), and the green emissions were often stronger than the red emissions. [ 38,57–62,64 ] Here, all Er‐MgAl‐LDH‐ n ( n = 1, 2, 3, 4) exhibited strong infrared emissions at 720, 780, and 850 nm under 480, 520, and 565 nm excitations, respectively, along with red emission at 650 nm under 220 nm excitation (seen in Figure 6II and Figure 7). Strong emissions at 720, 780, and 850 nm have been seldom reported in previous downconverted emission spectra for Er 3+ ‐doped materials.…”

“…The emission at ~650 nm is often found in the downconversion emission spectra of Er 3+ ‐doped compounds [ 30,31,34,55,57 ] as well as the upconversion emission spectra of RE/Er 3+ co‐doped compounds. [ 33,35,58–64 ] When samples were excited with 480, 520, and 565 nm wavelengths, some strong emissions at 720, 780, and 850 nm, respectively, occurred, but the emission at 650 nm did not emerge. The possible reason is that the energy at 480, 520, and 565 nm wavelengths was too low to produce a 650 nm emission.…”

“…To understanding the origins of strong emissions at 720, 780, and 850 nm, the energy transfer diagram of Er 3+ doped into MgAl‐LDH‐ n ( n = 1, 2, 3, 4) is described (seen in Figure 9 and based on relevant references [ 30–35,38,42,55,58–61,67 ] and the relationship between the wavelength and energy is as follows: Electrons at ground state level ( 4 I 15/2 ) can absorb energy and jump to all high energy levels and convert to excited state electrons, while Er 3+ ‐doped Mg n Al‐LDH‐n ( n = 1, 2, 3, 4) were excited by the 220 nm wavelength (5.64 eV). When the excited state electrons come back to the ground state, some excited state electrons may release energy by nonradiative transition, and some excited state electrons at 4 F 9/2 energy level may release energy by radiative transition, resulting in the 650 nm emission.…”

Controllable multi‐color upconversion in glass ceramics through engineering crystal lattice distortion

“…The GCs contained ink was prepared via mixing certain amount of GCs powder in a solution of solution of solid PAA, HNO 3 , and ethanol. 1 g PAA was dissolved in 0.5 ml HNO 3 and 15 ml ethanol and stirred for 5 h. Then, 1 g GCs powder were added into the above solution and stirred for another 1 h to obtain the GCs‐contained ink, which was similar to our previous work 32 …”