Novel Y2(SO4)3:Eu3+ Phosphors with Anti-Thermal Quenching of Luminescence Due to Giant Negative Thermal Expansion

One of the most critical problems for phosphors used in light-emitting diodes (LEDs) is the thermal quenching of luminescence. Herein, novel (Y1−xEux)2(SO4)3 (x = 0, 0.17, 0.33, 0.5, 0.66) phosphors with anti-thermal quenching of luminescence due to giant negative thermal expansion were obtained by crystallization from aqueous solutions. The Y2(SO4)3 crystal structure is described as a framework, which consists of corner-sharing SO4 tetrahedra and YO6 octahedra. Thermal expansion of x = 0, 0.17, 0.5 solid solutions was investigated by high-temperature powder X-ray diffraction. The crystal structure of the x = 0.5 solid solution was refined by the Rietveld refinement using X-ray powder diffraction data at 400 and 500 °C to RB = 1.7 and 1.9%, respectively. The rotation of the SO4 tetrahedra results in giant negative volumetric thermal expansion: the structure contracts in all directions (αa = −7(3), αb = −15(3), αc = −22(2), αV = −44(2) · 10−6 °C−1 at 500 °C for YEu(SO4)3). The photoluminescence intensity is enhanced 1.8 times with the temperature increasing up to 500 °C. The anti-thermal quenching of Eu3+ luminescence can be described in terms of thermal-enhanced energy transfer between Eu3+ ions due to the negative thermal expansion of the Y2(SO4)3 matrix in all non-equivalent directions.