The tellurophosphate K₄P₈Te₄: Phase-change properties, exfoliation, photoluminescence in solution and nanospheres

We describe the inorganic polymer K₄P₈Te₄ which is soluble, giving solutions that exhibit white emission upon 355 nm laser irradiation. An indirect band gap semiconductor (E_g ≈ 1.4 eV), K₄P₈Te₄ crystallizes in the space group P2 ₁/m, with a = 6.946(1) Å, b = 6.555(1) A, c = 9.955(2) Å, and β = 90.420(3)° at 173(2) K. The compound features infinite chains of [P₈Te₄^4-] with covalent P-Te bonding and exhibits reversible crystal-glass phase-change behavior. When deposited from solution, the material forms highly crystalline K₄P ₈Te₄ nanospheres. The thermal analysis, FT-IR, UV-vis diffuse reflectance, ³¹P magic angle spinning solid-state NMR spectroscopy, and pair distribution function (PDF) analysis for the crystal and glass forms and ab initio electronic structure calculations by the screened-exchange local density function approximation are also reported. Speciation of K₄P₈Te₄ in solution studied with ³¹P solutionstate NMR spectroscopy, electrospray ionization mass spectrometry, and PDF analysis indicate exfoliation of [P₈Te ₄^4-] chains followed by rearrangement into molecular species.