Crystal Phase Transition and Polyhedron Transformation Towards the Evolution of Photoluminescence and the Improvement of Thermal Stability in Efficient Blue-Emitting Ba0.47-xSr0.50+xAl2Si2O8:Eu2.

Investigations into novel single-phase phosphors with outstanding luminescence properties and excellent thermal stability are urgently needed in the lighting field. In this work, a crystal phase transition and polyhedron transformation strategy via cation substitution has been proposed. Via controlling the Sr/Ba ratio, the structural evolution of the phosphor from a monocelsian phase to a hexacelsian or feldspar phase and the variation of the local environments of Eu2+ sites are correspondingly studied in Ba0.47-xSr0.50+xAl2Si2O8:0.03Eu. Consequently, the optimal Ba0.17Sr0.80Al2Si2O8:0.03Eu sample exhibits a higher intensity, up to 15.2-fold that of Ba0.97Al2Si2O8:0.03Eu. A narrower full-width-at-half-maximum of 73 nm, better color purity of 82.96%, and an internal quantum yield of 82.3% can be realized. With an increase in temperature, the emission intensity losses of samples from x = -10.0-47.0% are no more than 10.0% at 473 K. Moreover, a WLED (CCT = 5210 K; CRI = 90.3) fabricated using Ba0.17Sr0.80Al2Si2O8:0.03Eu displays warmer white light than one fabricated using BaMgAl10O17:Eu under the same assembly and test conditions. Analysis shows that the structural evolution with reduced polyhedral symmetry and the condensed crystal structure with fortified rigidity are responsible for the improvement in properties. This discovery demonstrates that the utilization of a crystal phase transition and symmetrical coordination is an efficient way to develop novel efficient phosphors and other related materials.