Abstract

A new strategy is reported to enhance the upconversion (UC) luminescence emission of LiYF₄:Yb, Er nanocrystals (NCs) using magnesium as a dopant. We carried out systematic experimental studies on the crystal structure, grain size, and UC emitting property of the tetragonal LiYF₄:Yb, Er with varied concentrations of Mg²⁺. The UC luminescence properties were examined under 980 nm laser illumination with various excitation power densities. At a proper doping concentration, co-doping of Mg²⁺ ions into LiYF₄:Yb, Er is found to result in efficient reinforcement in both the green and red upconverted emissions. Remarkably, the maximum green and red luminescence intensities were reinforced by sevenfold and fivefold, respectively, when 7 mol% Mg²⁺ was co-doped into tetragonal LiYF₄. The possible origin and mechanism for boosting UC emission were explained according to the alteration of the cell volume and the local crystal field surrounding the Er³⁺ ions by co-doping of Mg²⁺. Moreover, the emission-optimized LiYF₄ UCNCs were further investigated to understand thermal-sensing behaviors employing the fluorescence intensity ratio (FIR) approach from the two neighboring thermal coupled states (²H_11/2/⁴S_3/2). The optimization of Mg²⁺ co-doping in LiYF₄:Yb, Er allowed the resultant UCNCs to be an excellent luminescent thermometer over a wide range of temperature. Applying the optimized UCNCs as an optical thermometer, a maximum thermal sensitivity (S) of 5.43 × 10^–2 K⁻¹ was achieved at room temperature and a low-power excited upconversion (1 W cm⁻²). The achieved S value is more advanced than most of the Er-based nanophosphors reported heretofore. This paper provides a perspective scheme to design and grow high-quality upconversion nanomaterials for achieving the preconditions of the pragmatic application in temperature sensing, optically heating, and color display devices.

中文翻译：

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高亮度和灵敏的测温LiYF 4：Yb，Er通过Mg 2+三掺杂上转换纳米晶体

摘要

据报道，使用镁作为掺杂剂，可以增强LiYF ₄：Yb，Er纳米晶体（NCs）的上转换（UC）发光发射的新策略。我们对不同浓度的Mg ²⁺的四方LiYF ₄：Yb，Er的晶体结构，晶粒尺寸和UC发射特性进行了系统的实验研究。在各种激发功率密度下，在980 nm激光照射下检查UC发光特性。在适当的掺杂浓度下，将Mg ²⁺离子共掺杂到LiYF _4中：Yb，Er被发现可以有效增强绿色和红色上转换后的发射光。显着地，当将7mol％的Mg ²⁺共掺杂到四方LiYF _4中时，最大绿色和红色发光强度分别增强了七倍和五倍。通过Mg ^2+的共掺杂，根据细胞体积和围绕Er ³⁺离子的局部晶体场的变化，解释了促进UC发射的可能起源和机理。此外，还对发射优化的LiYF ₄ UCNC进行了进一步研究，以从两个相邻的热耦合状态采用荧光强度比（FIR）方法了解热敏行为（²H _11/2 / ⁴ S _3/2）。LiYF ₄：Yb，Er中Mg ²⁺共掺杂的优化使所得的UCNC在宽温度范围内成为出色的发光温度计。将优化的UCNC用作光学温度计，在室温和低功率激发上转换（1 W cm ^-2）时可达到5.43×10 ^–2  K ^-1的最大热灵敏度（S ）。达到的S其值比迄今为止报道的大多数基于Er的纳米荧光粉更先进。本文提供了一种透视方案来设计和生长高质量的上转换纳米材料，以实现在温度传感，光学加热和彩色显示设备中实际应用的前提条件。