• 商用荧光粉的要求：
• YAG:Ce3+， CaAlSiN3:Eu2+目前还是最好的商用荧光粉，outcompete rapidly developing alternatives。
  • 优点：a close to 100% internal quantum yield and prolonged LED operating hours without severe degradation.
  • 缺点：thermal quenching or saturation quenching (automotive head lights and projector devices)
• 对于high-power applications应用场景，目前只有YAG:Ce3+满足要求，没有可用的红色荧光粉。

Two-level systems $$\frac{\mathrm{d}p}{\mathrm{d}t}=k_{\mathrm{exc}}[1-p(t)]-k_{\mathrm{decay}}p(t)$$(1) $p(t)$ is the probability to find a center in the excited state at some moment in time $t$;
(2) $k_{\mathrm{exc}}=\sigma I_{\mathrm{exc}}/\hslash \omega$ is the rate constant for excitation, depends on the absorption cross-section $\sigma$ of a center, , the excitation intensity $I_{\mathrm{exc}}$, , and on the excitation photon energy $\hslash \omega$;
(3) $k_{\text{decay }}$ is the rate constant for decay, $=k_{\text{rad }}+k_{\text{nonrad }}$.

两种情况：

• $t>t_2$
  $p(t)=p\left(t_2\right)e^{-k\text{decay }(t-t2)}$
• $t_1<t<t_2$
  $p(t)=p\left(t_2\right)[1-e^{-k_{\text{rise }}(t-t_1)}]$其中$k_{\text{rise }}=k_{\text{exc }}+k_{\text{decay }}$

可以被测定的参数：As the emission intensity from the sample is proportional to excited-state population, both $k_{\text{exc }}$ and $k_{\text{decay }}$ can be determined from a measurement of the luminescence dynamics with square-wave-modulated excitation.

KSF:Mn⁴⁺ Mild experiment conditions
(1) the grains were placed on an indium foil directly connected to a heat sink; (2) the peak excitation intensity was limited to a maximum of 0.7 W mm⁻²;
(3) the duty cycle was set to no more than 5%;
(4) the heat sink waskept at room temperature.

• Mn4+的激发态寿命为8.5 ms，和之前光谱仪测试的一致，而且这里没有随着激发功率的变化而变化，说明没有在这个实验条件下没有open nnradiative decay pathways。
• 激发光为blue，发射光为red，所以必然存在热的生成，但是寿命没有变化，说明在此条件下not sufficient to lead to thermal quenching.
• rise dynamics accelerate with increasing excitation intensity，这很容易理解，因为$k_{\text{rise }}=k_{\text{exc }}+k_{\text{decay }}$