Phase-pure eulytite-type Sr₃Y_0.88(PO₄)₃:0.10Yb³⁺,0.02Ln³⁺ upconversion (UC) phosphors (Ln = Ho, Er, Tm) were synthesized via gel-combustion and subsequent calcination at 1250°C. Their UC luminescence, temperature-dependent fluorescence intensity ratio of thermally and/or non-thermally coupled energy levels, and performance of optical temperature sensing were systematically investigated. The phosphors typically exhibit green, orange-red and blue luminescence under 978 nm NIR laser excitation for Ln = Er, Ho and Tm, respectively, which were discussed from two- and three-photon processes. The 524 nm green (Er³⁺), 657 nm red (Ho³⁺) and 476 nm blue (Tm³⁺) main emissions were analyzed to have average decay times of ~52 ± 2, 260.6 ± 0.7 and 117 ± 1 μs, respectively. It was shown that (1) the Er³⁺ doped phosphor has a better overall performance of temperature sensing with thermally coupled ²H_11/2 and ⁴S_3/2 energy levels, whose maximum absolute (S_A) and relative (S_R) sensitivities are ~5.07 × 10⁻³ K⁻¹ at 523 K and ~1.16% at 298 K, respectively; (2) the Ho³⁺ doped phosphor shows maximum S_A and S_R values of ~0.019 K⁻¹ (298–573 K) and 0.42% at 573 K for the non-thermally coupled energy pairs of ⁵F₅/(⁵F₄,⁵S₂) and ⁵I₄/⁵F₅, respectively; (3) the Tm³⁺ doped phosphor has a maximum S_A of ~12.74 × 10⁻³ K⁻¹ at 573 K for the non-thermally coupled ³F_2,3/¹G₄ energy levels and a maximum S_R of ~1.74% K⁻¹ at 298 K for the thermally coupled ³F_2,3/³H₄ levels. Advantages of the current phosphors in optical temperature sensing were also revealed by comparing with other typical UC phosphors. Graphical abstract Phase-pure eulytite-type Sr₃Y_0.88(PO₄)₃:0.10Yb³⁺,0.02Ln³⁺ upconversion (UC) phosphors (Ln=Ho, Er, Tm) were synthesized via gel-combustion, whose property and mechanism of UC luminescence and the performance of optical temperature sensing with thermally and/or non-thermally coupled energy levels were thoroughly investigated.

Doping Li⁺ resulted in oxygen vacancies and green-yellow emission. Changing the excitation wavelength/temperature yielded varied visible/NIR lights and afterglows, which contributed to a dynamic luminescence.

Conductive copper patterns are usually heated in vacuum, inert gas or reducing atmosphere to avoid the oxidation of copper for printed electronics applications. Here, we report a formulation of metal organic decomposition copper ink and obtained conductive copper films by heating the ink in air at low temperatures using diamine as the complexing agent without other additions. The complexing of diamine with the copper formate tetrahydrate precursor lowers the thermal decomposition temperature of the ink, promotes the densification of the film and prevents the oxidation of copper by consuming absorbed oxygen during the heating process. The copper films using 1,2-diaminopropane as the complexing agent showed a low resistivity of 1.8 × 10⁻⁵ Ω cm after heating at 180 °C for 1 min in air. The pen-writing copper patterns showed a metal copper luster and great adhesion on a PI substrate.