Pure red fluorescence generated by near infrared (NIR) excitation is desired for bio-imaging with high biological penetration, but without cell damage or multi-photon photo-toxicity. In this work, β-NaYF₄:Er³⁺ and β-NaYF₄:Er³⁺,Tm³⁺ microcrystals were synthesized using a novel hydrothermal method. β-NaYF₄:Er³⁺ microcrystals exhibited intense green and red up-conversion emissions under 976 nm laser diode excitation. The introduction of Tm³⁺ ions into β-NaYF₄:Er³⁺ resulted in strong inhibition of green up-conversion emission (Er³⁺:²H_11/2 /⁴S_3/2→⁴I_15/2) and, consequently, red up-conversion emission (Er³⁺:⁴F_9/2→⁴I_15/2) was significantly promoted. To simultaneously restrain green up-conversion emissions and enhance red up-conversion emissions, the optimal concentrations of Er³⁺ and Tm³⁺ ions were determined to be 20 mol% and 2.0 mol%, respectively. The red/green up-conversion emission intensity ratio increased from ~1.80 (β-NaYF₄:20Er³⁺, mol%) to ~78 (β-NaYF₄:20Er³⁺,2Tm³⁺, mol%) after the addition of 2 mol% Tm³⁺ ions to β-NaYF₄:20Er³⁺ (mol%). The red up-conversion emission intensity of β-NaYF₄:20Er³⁺,2Tm³⁺ was stronger than that for commercial red up-conversion phosphors (NaYF₄ and ZnF₂) under the same experimental conditions. Based on the results of the emission spectra, luminescence rise, and decay profiles, the mechanism of enhanced red up-conversion emission by Tm³⁺ ion co-doping in β-NaYF₄:20Er³⁺,2Tm³⁺ (mol%) was proposed. The bio-fluorescence experiment under NIR excitation proves that β-NaYF₄:Er³⁺,Tm³⁺ microcrystals have potential applications in bio-imaging.

近红外 (NIR) 激发产生的纯红色荧光对于具有高生物穿透性但没有细胞损伤或多光子光毒性的生物成像来说是理想的。本工作采用新型水热法合成了β-NaYF ₄ :Er ³⁺和β-NaYF ₄ :Er ³⁺ ,Tm ^3+微晶。β-NaYF ₄ :Er ³⁺微晶在 976 nm 激光二极管激发下表现出强烈的绿色和红色上转换发射。将Tm ³⁺离子引入β-NaYF ₄ :Er ³⁺导致强烈抑制绿色上转换发射(Er ³⁺ : ²H _11/2 / ⁴ S _3/2 → ⁴ I _15/2 )，从而显着促进了红色上转换发射(Er ³⁺ : ⁴ F _9/2 → ⁴ I _{15/2 )。}^{为了同时抑制绿色上转换排放和增强红色上转换排放，确定Er 3+}和Tm ³⁺离子的最佳浓度分别为20 mol%和2.0 mol%。红/绿上转换发光强度比从~1.80 (β-NaYF ₄ :20Er ³⁺ , mol%) 增加到~78 (β-NaYF ₄ :20Er ³⁺在β-NaYF ₄ :20Er 3+ ⁽ mol%)中加入2 mol% Tm ^{3+离子后的.2Tm 3+} , mol%)。在相同的实验条件下，β-NaYF ₄ :20Er ³⁺ ,2Tm ³⁺的红色上转换发光强度强于商用红色上转换荧光粉（NaYF ₄和ZnF _{2 ）。}基于发射光谱、发光上升和衰减曲线的结果，Tm ³⁺离子共掺杂在β-NaYF ₄ :20Er ³⁺ ,2Tm ^{3+中增强红色上转换发射的机制}(mol%) 被提议。NIR激发下的生物荧光实验证明β-NaYF ₄ :Er ³⁺ ,Tm ³⁺微晶在生物成像方面具有潜在的应用价值。