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.

中文翻译：

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La2O2SO4：RE / Yb新型荧光粉，用于近红外到可见光和近红外上转换发光（RE = Ho，Er，Tm）

La ₂ O ₂ SO ₄：RE / Yb（分别为RE = Ho，Er和Tm ）的3种新的上转换（UC）荧光粉是通过在100°C水热合成的层状氢氧化物前体的便捷脱水而得到的。Rietveld XRD精炼发现，随着RE ³⁺尺寸的减小，晶胞尺寸缩小，从而证实了固溶体的直接结晶。Er ³⁺和Ho ³⁺活化剂在978 nm近红外（NIR）激光激发（NIR-Vis UC）下均同时显示绿色和红色（主要）发射。特别是，Tm ³⁺通过其³ H ₄  → 在〜812 nm处产生了高斯形的纯近红外发射带。³ H ₆跃迁（NIR-NIR UC），这对于NIR生物应用是非常需要的。对激发功率相关的UC特性的分析表明，这3种荧光粉具有3光子机理，并说明了导致UC的可能的光子反应。