Comparing the optical properties and thermal stability of green (TbPO4), yellow (DyPO4), and red (PrPO4) emitting single crystal samples

Abstract

Blue, green and red-emitting phosphors for near-UV/blue based phosphor blend converted white-light emitting devices have been investigated extensively over the past years. Herein, we present our results on the optical spectroscopy of single crystal samples of TbPO₄, DyPO₄ and PrPO₄ exhibiting prominent emission at green (545 nm), yellow (574 nm) and red (616 nm) region of the electromagnetic spectrum, respectively. We study the temperature dependence of their emission spectra for excitations at 365 and 455 nm, to mimic experimental conditions for phosphor converted light emitting diodes, to show that their thermal quenching temperature is 730 K for TbPO₄ (excitation 365 nm), 490 and 520 K for DyPO₄ (excitation at 365 and 455 nm), and 540 K for PrPO₄ (excitation 455 nm). The TbPO₄ emission does not show any considerable blue/red shift at elevated temperatures, while DyPO₄ emission is observed close to the center of CIE coordinate diagram. The PrPO₄ sample possesses high color purity which shows slight yellow-shift at elevated temperatures. The ground state of Pr³⁺ and Tb³⁺ are found to be within the band gap suggesting that both are able to trap holes from the valence band as evinced from the thermoluminescence glow curve data which shows peak maxima at 422 and 437 K due to hole release from the Pr⁴⁺ and Tb⁴⁺, respectively. The result suggests that the samples have large potential for solid state lighting devices upon choice of an appropriate excitation wavelength.