Phase-sensitive radioluminescence and photoluminescence features in Tm-doped yttrium tantalates for cyan and white light generation.

Radioluminescence and visible photoluminescence tunability features from a single Tm-doped yttrium tantalate phosphor prepared by a soft sol-gel method designed to afford cubic YTaO and monoclinic M'-YTaO crystalline phases are reported. The annealing temperature influenced the crystallization kinetics and stabilized a preferential phase. To investigate how the crystalline phase affected the Tm optical properties, excitation and emission spectra in the visible range were recorded for the samples annealed at 900 or 1100 °C. Inhomogeneous broadening in the emission spectra was due to the structural disorder of the YTaO phase. Energy transfer between the yttrium tantalate host and Tm ions was observed upon CT band excitation. Under UV light, an intense and tunable cyan to blue emission ascribed to both the Tm transitions D → F and G → H also emerged and could be observed by the naked eye. The lifetime decay curves demonstrated the occupation of distinct sites and that the symmetry sites occupied by Tm ions in the YTaO host have higher lifetime values than in the M'-YTaO phase. A radioluminescence study was carried out to evaluate the yttrium tantalate scintillation performance, which was considerably enhanced in the presence of the M'-YTaO phase. Intense white light emission displaying a large color correlated temperature range could be obtained by controlling the delay time for the time-resolved measurements and upon an orange-emitting phosphor addition. All the above-mentioned structural and photoluminescence properties make these Tm-doped yttrium tantalates potential candidates for photonic applications, particularly integrated w-LED systems.