Non-quenching photoluminescence emission up to at least 865 K upon near-UV excitation in a single crystal of orange-red emitting SmPO4

Abstract

The adjustment of photoluminescence emission spectrum and an enhancement in the thermal stability of red/orange-red emitting phosphors is an important issue for the whole lighting industry. Herein, we present our results on the luminescence spectroscopy of a single crystal sample of SmPO₄ exhibiting a prominent orange-red emission at 597 nm, along with a charge-transfer absorption (O²⁻ → Sm³⁺) around 200 nm. We study the temperature dependence of emission spectra in SmPO₄ for excitations at 365 and 455 nm, to mimic experimental conditions for phosphor converted light emitting diodes, to show that the sample has a non-quenching photoluminescence emission up to at least 865 K for an excitation at 365 nm, and ∼865 K for an excitation at wavelength, 455 nm. The thermal stability of SmPO₄ was found to be much higher than its structural analogue, EuPO₄, which is also an orange-red emission phosphor, but possesses a thermal quenching temperature of 710 K (exc. 365 nm), and 735 K (exc. 455 nm). The extraordinary thermal stability of SmPO₄ is a result of the energy transfer from deep defects to the Sm³⁺ ions at high temperatures. The color purity of SmPO₄ (65%) was found to be slightly lower than the EuPO₄ sample (70%), at room temperature. The results suggests that the rare earth orthophosphate, SmPO₄, has a large potential for near-UV excited phosphor converted solid state lighting devices.