A novel precursor route for Y2Mo4O15:Yb3+,Ho3+ phosphor and investigation of up-conversion luminescence

Abstract

Hydrothermal reaction of Y(NO3)3·6H2O and (NH4)6Mo7O24·4H2O at 180 °C for 24 h was performed in this work via systematically varying the solution pH (4–10) and Mo/Y molar ratio (R, 2–5), which produced a NH4Y(MoO4)2·0.19H2O new compound that yielded phase-pure Y2Mo4O15 upon calcination at 500–700 °C. The pH/R window for the compound to crystallize was determined to be 6–7/3 and 6–9/4–5. The products were characterized in detail by XRD, FTIR, elemental analysis, SEM, TEM, STEM and TG to understand chemical composition and the courses of phase/morphology evolution. Applying the above synthesis strategy successfully produced Y2Mo4O15:xYb3+,yHo3+ phosphors that exhibit strong deep-red (630–670 nm, 5F5 → 5I8 transition) and weak green (530–560 nm, 5F4/5S2 → 5I8) emissions under 978 nm laser pumping, where the optimal Yb3+ and Ho3+ contents were determined to be x = 0.20 for y = 0.01 and y = 0.03 for x = 0.10, respectively. Spectral analysis indicated that the up-conversion luminescence occurred via a two-photon process, with the red/green intensity ratio and also the emission color dependent on Yb3+ and Ho3+ contents, which were explained by considering ground state excitation, energy transfer, non-radiative relaxation and cross relaxation.