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In the quest to predict photoluminescent efficiency in rare-earth substituted inorganic phosphors, research has shown that materials consisting of ordered, rigid crystal structures tend to possess the highest photoluminescent quantum yields. A compound's Debye temperature (ΘD), which can be calculated using ab initio calculations, is an ideal proxy for quantitatively comparing structural rigidity among different inorganic compounds, allowing potentially efficient phosphors to be selected from large crystal structure databases. However, the high computational cost of these calculations limits estimating ΘD for unsubstituted host crystal structures only. It is assumed that the low substitution concentration of the rare-earth luminescent center does not significantly influence a material's Debye temperature. This work evaluates the validity of this approximation by examining the effect of luminescent center substitution on a host structure's ΘD. Two well-known phosphors, (Y1–xCex)3Al5O12 (x = 0 − 0.05) and Ba1-δEuδMgAl10O17 (δ = 0 − 0.15), were synthesized with varying rare-earth concentrations, while ΘD was computationally estimated and then determined by ultrasonic pulse-echo speed-of-sound and low-temperature heat capacity measurements. The ensuing results provide key implications for using ΘD as a proxy for structural rigidity in substituted inorganic compounds. [ABSTRACT FROM AUTHOR]

A series of Eu 2+ -substituted yellow-green emitting phosphors based on the compound, Sr 6 M 2 Al 4 O 15 ( M = Y, Lu, Sc) were identified as potential efficient phosphors based on their high calculated Debye temperatures (Θ D > 450 K), which acts as a proxy for photoluminescent quantum yield (PLQY). The crystal structure contains corner-sharing [ M O 6 ] octahedra and [AlO 4 ] tetrahedra leading to a highly connected, densely packed crystal structure. However, contrary to prediction, these compounds all showed a low PLQY (<6.5%) at room temperature. Temperature dependent luminescence measurements indicate that the photoluminescence is intense at 80 K but loses ≈90% of the emission intensity by room temperature, with the thermal quenching temperature ( T 50 ) occurring well below room temperature. These results suggest that even though Debye temperature (Θ D ) is a valid proxy for PLQY, it does not describe thermal quenching. [ABSTRACT FROM AUTHOR]