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Abstract: The 3 new upconversion (UC) phosphors of La2O2SO4:RE/Yb (RE=Ho, Er, and Tm, respectively) were derived via facile dehydration of their layered hydroxide precursors that were hydrothermally synthesized at 100°C. Rietveld XRD refinement found contracting cell dimension with decreasing RE3+ size, confirming the direct crystallization of solid solution. The Er3+ and Ho3+ activators both exhibited simultaneous green and red (dominant) emissions under 978‐nm near‐infrared (NIR) laser excitation (NIR‐Vis UC). Particularly, Tm3+ produced a Gaussian‐shaped pure NIR emission band at ~812 nm via its 3H4 → 3H6 transition (NIR‐NIR UC), which is highly desired for NIR biological application. Analysis of the excitation‐power dependent UC properties manifested a 3‐photon mechanism for the 3 phosphors, and the possible photon reactions leading to UC were illustrated. [ABSTRACT FROM AUTHOR]

The sulfate-type layered hydroxides of (Gd1− xTb x)2( OH)5( SO4)0.5· nH2O ( x = 0.06-0.10) have been directly crystallized via hydrothermal reaction at 120°C and pH ~10.0, without the need of conventional anion exchange. The primary crystallites were found to be thin platelets having lateral sizes of ~450-1000 nm and thicknesses of ~65-85 nm. Combined analysis by DTA/ TG, FTIR, and XRD revealed that the layered compounds convert into cubic (Gd1− xTb x)2O3 solid-solutions through dehydration, dehydroxylation, and desulfuration up to ~1200°C and via a (Gd1− xTb x)2O2.5( SO4)0.5 intermediate phase. Optical spectroscopies found that the layered compounds and the derived oxides have their strongest 4 f8→4 f75 d1 transition excitations at ~248 and 305 nm and optimal Tb3+ contents of 9 at.% ( x = 0.09) and 8 at.%, respectively. Both the types of materials exhibit the strongest emission at ~544 nm (the 5D4→7F5 transition of Tb3+), but the oxide has an emission intensity ~3 times that of the hydroxide. Fluorescence lifetime of the 544 nm green emission was found to decrease from 2.45 to 2.15 ms along with increasing Tb3+ content for the oxide, and smaller values of ~1.55 ms were derived for the layered hydroxides. [ABSTRACT FROM AUTHOR]