Thermal ionization and thermally activated crossover quenching processes for $5d-4f$ luminescence in ${\mathrm{Y}}_3\mathrm{A}{\mathrm{l}}_{5-x}\mathrm{G}{\mathrm{a}}_x{\mathrm{O}}_{12}:\mathrm{P}{\mathrm{r}}^{3+}$

We investigated thermally activated ionization and thermally activated crossover as the two possibilities of quenching of $5d$ luminescence in $\mathrm{P}{\mathrm{r}}^{3+}$-doped ${\mathrm{Y}}_3\mathrm{A}{\mathrm{l}}_{5-x}\mathrm{G}{\mathrm{a}}_x{\mathrm{O}}_{12}$. Varying the Ga content $x$ gives the control over the relative energy level location of the $5d$ and $4f^2:{}^{3}P_J$ states of $\mathrm{P}{\mathrm{r}}^{3+}$ and the host conduction band (CB). Temperature-dependent luminescence lifetime measurements show that the $5d$ luminescence quenching temperature $T_{50\%}$ increases up to $x=2$ and decreases with further increasing Ga content. This peculiar behavior is explained by a unique transition between the two quenching mechanisms which have an opposite dependence of thermal quenching on Ga content. For low Ga content, thermally activated crossover from the $4f5d$ state to the $4f^2\left({}^{3}P_J\right)$ states is the operative quenching mechanism. With increasing Ga content, the activation energy for thermally activated crossover becomes larger, as derived from the configuration coordinate diagram, while from the vacuum referred binding energy diagram the activation energy of thermal ionization becomes smaller. Based on these results, we demonstrated that the thermal quenching of $\mathrm{P}{\mathrm{r}}^{3+}:5d_1-4f$ luminescence in ${\mathrm{Y}}_3\mathrm{A}{\mathrm{l}}_{5-x}\mathrm{G}{\mathrm{a}}_x{\mathrm{O}}_{12}$ with $x=0,1,2$ is a thermally activated crossover while for $x=3,4,5$ it results from the thermal ionization.

Figure 1

Schematic diagram combining configuration coordinate (CC) and VRBE diagrams for YAG:$\mathrm{C}{\mathrm{e}}^{3+}$ and YAG:$\mathrm{P}{\mathrm{r}}^{3+}$ explaining thermal quenching of luminescence.

Figure 2

PL and PLE in ${\mathrm{Y}}_3\mathrm{A}{\mathrm{l}}_5{\mathrm{O}}_{12}$ doped with $0.2\%\mathrm{P}{\mathrm{r}}^{3+}$ and $0.1\%\mathrm{C}{\mathrm{e}}^{3+}$.

Figure 3

PL (for excitation to the $5d_1$ state) and PLE (for $5d_1-4f$ luminescence) of ${\mathrm{Y}}_3\mathrm{A}{\mathrm{l}}_{5-x}\mathrm{G}{\mathrm{a}}_x{\mathrm{O}}_{12}:0.2\%\mathrm{P}{\mathrm{r}}^{3+}$ ($x=0,1,2,3,4$) at 10 K. For the $x=5$ samples, PLE was measured by monitoring ${}^{3}P_J$ luminescence.

Figure 4

High-resolution PL spectrum (excited by 280 nm) and PLE spectrum (of 318 nm luminescence) in YAG:$0.2\%\mathrm{P}{\mathrm{r}}^{3+}$ at 8 K. Vertical black lines are phonon lines.

Figure 5

(a) Configuration coordinate diagram showing the various $4f^2$ and $4f5d$ states of $\mathrm{P}{\mathrm{r}}^{3+}$ in YAG:$\mathrm{P}{\mathrm{r}}^{3+}$ and (b) enlarged view of the CC diagram around the crossing point of the lowest energy $4f5d_1$ state with the highest energy $4f^2$ states (${}^{3}P_2$) for ${\mathrm{Y}}_3\mathrm{A}{\mathrm{l}}_{5-x}\mathrm{G}{\mathrm{a}}_x{\mathrm{O}}_{12}:\mathrm{P}{\mathrm{r}}^{3+}$ ($x=0-4$).

Figure 6

Temperature dependence of lifetime in ${\mathrm{Y}}_3\mathrm{A}{\mathrm{l}}_{5-x}\mathrm{G}{\mathrm{a}}_x{\mathrm{O}}_{12}:\mathrm{P}{\mathrm{r}}^{3+}$.

Figure 7

Integrated TL intensity between 300 K and 600 K as a function of charging excitation wavelength from 180 nm to 320 nm with 300 s charging time in ${\mathrm{Y}}_3\mathrm{A}{\mathrm{l}}_{5-x}\mathrm{G}{\mathrm{a}}_x{\mathrm{O}}_{12}:\mathrm{P}{\mathrm{r}}^{3+}$.

Figure 8

Tauc plot of PLE spectra in the VUV region in ${\mathrm{Y}}_3\mathrm{A}{\mathrm{l}}_{5-x}\mathrm{G}{\mathrm{a}}_x{\mathrm{O}}_{12}:\mathrm{P}{\mathrm{r}}^{3+}$.

Figure 9

Stacked VRBE diagram of ${\mathrm{Y}}_3\mathrm{A}{\mathrm{l}}_{5-x}\mathrm{G}{\mathrm{a}}_x{\mathrm{O}}_{12}:\mathrm{P}{\mathrm{r}}^{3+}$.