The upconversion (UC) emission properties of rare-earth ions are not only dependent on the host materials, but also relate to the excitation conditions. In this work, taking the Ho ³⁺ions for example, upconversion emission properties are studied in two NaYF ₄and LiYF ₄fluoride microcrystals through changing excitation conditions, namely the excitation power and the sample environment. The NaYF ₄:20%Yb ³⁺/2%Ho ³⁺and NaYF ₄:20%Yb ³⁺/2%Ho ³⁺microcrystal are synthesized by the hydrothermal method. The typical X-ray diffraction patterns of NaYF ₄:20%Yb ³⁺/2%Ho ³⁺and LiYF ₄:20%Yb ³⁺/2%Ho ³⁺microcrystal indicate that the prepared samples possess pure hexagonal phase NaYF ₄structure and the pure tetragonal phase LiYF ₄structure with high crystallinity, respectively. Most of NaYF ₄:20%Yb ³⁺/2%Ho ³⁺microcrystals show uniform and regular rod shape with diameter and length of approximately 3 μm and 10 μm, respectively. Few rods with a length of approximately 5 μm are also observed. The LiYF ₄:20%Yb ³⁺/2%Ho ³⁺microcrystals are all octahedral in shape with a smooth surface, the average size is around 10 μm. The spectral peculiarities of Ho ³⁺are investigated by using confocal microscopy equipment under near infrared 980 nm excitation. Beautiful patterns with different upconversion emissions of Ho ³⁺are discovered in single NaYF ₄and LiYF ₄microcrystal. As the excitation power increases, the upconversion emission of Ho ³⁺turns from green to pink in single NaYF ₄microrods due to the cross-relaxation between Ho ³⁺and the energy back transfer from Ho ³⁺to Yb ³⁺. However, in single LiYF ₄:Ho ³⁺microcrystal no similar phenomenon is observed. Nevertheless, when the powder of NaYF ₄and LiYF ₄microcrystals are excited by a 980 nm laser, increasing the power can turn the output colours of Ho ³⁺all green. Because particles outside the laser radiation are not directly covered by the laser, most of them are excited by the scattered light from the laser, and the actual excitation energy is low compared with at the center position. This result can be proved in the single NaYF ₄and LiYF ₄microcrystal under low excitation power. Thus, the results indicate that UC emission of rare-earth ions is controlled by changing the excitation condition. Using the new testing methods we can not only observe more interesting spectral phenomena, but also find a new way to further study its luminescence mechanism.