M²⁺Doping Induced Simultaneous Phase/Size Control and Remarkable Enhanced Upconversion Luminescence of NaLnF₄Probes for Optical-Guided Tiny Tumor Diagnosis

KGaA, Weinheim Doping has played a vital role in constructing desirable hybrid materials with tunable functions and properties via incorporating atoms into host matrix. Herein, a simple strategy for simultaneously modifying the phase, size, and upconversion luminescence (UCL) properties of the NaLnF4(Ln = Y, Yb) nanocrystals by high-temperature coprecipitation through nonequivalent M2+doping (M = Mg2+, Co2+) has been demonstrated. The phase transformation from cubic to hexagonal is readily achieved by doping M2+. Compared with Mg-free sample, a remarkable enhancement of overall UCL (≈27.5 times) is obtained by doping Mg2+. Interestingly, owing to the efficient UCL, red UCL-guided tiny tumor (down to 3 mm) diagnosis is demonstrated for the first time. The results open up a new way of designing high efficient UCL probe with combination of hexagonal phase and small size for tiny tumor detection.