Latent fingerprint development plays an important role in forensic sciences. In the last two decades, various fluorescent nanomaterials have been used to develop latent fingerprints, of which rare earth ion–doped upconversion nanomaterials (UCNMs) are outstanding examples. The use of UCNMs is advantageous for several reasons, including high contrast due to the strong fluorescence signal and negligible background interference, high sensitivity owing to the tunable nanoparticle size, and high selectivity arising from the proper particle morphology with suitable absorbability. In most cases, NaYF₄:Yb,Er UCNM-based development involves a single near-infrared (NIR)-to-visible (VIS) process, enabling the observation of fingerprints by detecting VIS light under NIR light excitation. Inspiringly, other infrequently used UCNMs, such as NaYbF₄:Tm, can irradiate both NIR and VIS emissions under NIR excitation, making it possible to develop latent fingerprints in dual modes, namely, through both NIR-to-NIR and NIR-to-VIS process. In this work, we synthesized high-quality NaYbF₄:Tm UCNMs as fluorescent markers for dual-mode development of latent fingerprints. We found that our NaYbF₄:Tm UCNM–based method exhibited high contrast, high sensitivity, high selectivity, and extensive applicability in fingerprint development under both NIR-to-VIS and NIR-to-NIR modes. We expect that this work will open up a new avenue in the application of UCNMs to develop latent fingerprints under dual modes in forensic sciences.

潜在指纹的发展在法医学中起着重要的作用。在过去的二十年中，各种荧光纳米材料已被用于开发潜在指纹，其中稀土离子掺杂的上转换纳米材料（UCNMs）是出色的例子。由于多种原因，使用UCNMs是有利的，包括由于强荧光信号而产生的高对比度和可忽略的背景干扰，由于可调的纳米颗粒尺寸而导致的高灵敏度以及由于具有适当吸收性的适当颗粒形态而产生的高选择性。在大多数情况下，NaYF ₄：Yb，Er基于UCNM的开发涉及单个近红外（NIR）到可见（VIS）的过程，从而可以通过在NIR光激发下检测VIS光来观察指纹。令人鼓舞的是，其他不常用的UCNM，例如NaYbF ₄：Tm，可以在NIR激发下照射NIR和VIS发射，从而有可能在双模式下（即通过NIR-to-NIR和NIR-to-to产生潜指纹） VIS过程。在这项工作中，我们合成了高质量的NaYbF ₄：Tm UCNMs作为荧光标记，用于潜在指纹的双模式开发。我们发现我们的NaYbF ₄：Tm基于UCNM的方法在NIR-to-VIS和NIR-NIR模式下均表现出高对比度，高灵敏度，高选择性以及在指纹开发中的广泛适用性。我们希望这项工作将为应用UCNMs开辟一条新途径，以在法医学的双模式下开发潜在指纹。