Designing a Thermally Robust Green-Emitting Phosphor Rb2HfSi2O7: Eu2+ by an Atomic Chain Vibration Model and Its White Light-Emitting Diode Application

Thermal stability is considered to be a crucial factor to assess phosphors, which prompts people to explore the novel thermally robust phosphors and reveal the thermal quenching mechanism. Commonly, two mainstream theories of the thermal ionization mechanisms and cross-over well explain the thermal quenching and predict that the phosphors with a rigid network formed by anionic groups would present an excellent thermal stability; nevertheless, the effect of counterions is ignored. In this study, a significant Rb-based green-emitting phosphor of Rb2HfSi2O7: Eu2+ with an excellent thermal stability was successfully synthesized. The large difference in the thermal behavior of the three matrixes of M2HfSi2O7: Eu2+ (M = Na, K, and Rb) demonstrates the irreplaceable role of the counterion M (M = Na, K, and Rb) in thermal quenching. Thus, we proposed the atomic chain vibration model to describe the vibration of the counterion, which well illustrates the thermal behaviors of the three matrixes and makes up the weakness of the two prevailing theories. Moreover, the structure–property relation of Rb2HfSi2O7: Eu2+ was discussed to reveal its fascinating photoluminescence and cathodoluminescence properties, and a warm white light-emitting diode device showing a low correlated color temperature (4123 K) and a high color rendering index (88) was fabricated, which indicates the potential application of Rb2HfSi2O7: Eu2+ in white light-emitting diodes.