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激光制冷问题的核心是材料的选择。荧光中心能级的间距是其中的一个关键指标。确定合理的能级间距有助于选择合适的激光制冷材料。能级间距决定了对激光制冷至关重要的两个因素：量子效率和无辐射跃迁速率。如果单纯地从制冷功率的角度来看，能级间距越大量子效率越高，也越有利于荧光制冷。但当能级间距宽到某一值后，制冷功率基本上保持不变。如果从热一光转换效率的观点来考察激光制冷的效率问题，能级间距宽度的合理取值就应该小得多。如果在选择激光制冷材料时，确定制冷功率具有第一位的重要性，那么，能级间距选择在５０００ｃｍ－１左右的宽度是比较合适的、这不仅可以确定较大的热－光转换效率，同时也基本上保证了很高的制冷功率。
The core of the laser refrigeration problem is the choice of materials. Fluorescent center level spacing is one of the key indicators. Determining a reasonable energy level spacing helps select the appropriate laser refrigeration material. Energy level spacing determines two crucial factors for laser cooling: quantum efficiency and nonradiative transition rates. If simply from the cooling power point of view, the larger the energy level spacing, the higher the quantum efficiency, the more conducive to fluorescent refrigeration. However, when the level spacing wide to a certain value, the cooling power basically remains unchanged. If you look at the efficiency of laser cooling from the thermal-to-light conversion efficiency point of view, the reasonable value of the energy gap should be much smaller. If the choice of laser refrigeration materials, cooling power to determine the importance of the first place, then the energy level spacing in the choice of about 5000cm-1 width is more appropriate, which not only determine the larger heat - light conversion efficiency, At the same time it basically guarantees a high cooling power.