White or tunable photoluminescence of phosphors is of great significance for their practical applications in the light-emitting diodes. In this work, Ba 2 Y(BO 3 ) 2 Cl:Bi 3+ ,Eu 3+ phosphors were fabricated, and their photoluminescence properties were investigated. Three difference luminescence peaks located at 366, 410, and 490 nm were observed in the single Bi 3+ -doped Ba 2 Y(BO 3 ) 2 Cl phosphor under the excitation of ultraviolet light attributed to three various Bi 3+ sites occupied in the Ba 2 Y(BO 3 ) 2 Cl host. By tuning the excitation wavelength from three various Bi 3+ sites, the tunable luminescence properties were obtained. The energy transfer from Bi 3+ at various sites to Eu 3+ were observed in the Ba 2 Y(BO 3 ) 2 Cl:Bi 3+ ,Eu 3+ phosphors by an electric dipole−dipole interaction. The tunable and white luminescence was obtained by changing the Eu 3+ concentration or excitation wavelength. The light-emitting diodes with the white light emission were constructed by coupling Bi 3+ and Eu 3+ codoped Ba 2 Y(BO 3 ) 2 Cl phosphors with the UV chip, which indicated that the Bi 3+ and Eu 3+ codoped Ba 2 Y(BO 3 ) 2 Cl phosphors can act as a promising candidate for the UV converted WLEDs.

Reversible luminescence modulation of upconversion phosphors has the potential applications as photoswitches and optical memory and data storage devices. Previously, the photochromic reaction was extensively used for the realization of reversible luminescence modulation. It is very necessary to develop other approaches such as thermomchromic reaction to obtain the reversible upconversion luminescence modulation. In this work, the WO:Yb,Er phosphors with various colors were prepared at various temperatures, exhibiting tunable upconversion luminescence attributed to the formation of oxygen vacancies in the host. Upon heat treatment in the reducing atmosphere or air, the WO:Yb,Er phosphors show a reversible thermomchromic property. The reversible upconversion luminescence modulation of WO:Yb,Er phosphors was observed based on thermomchromic reaction. Additionally, the upconversion luminescence modulation is maintained after several cycles, indicating its excellent stability. The WO:Yb,Er phosphors with reversible upconversion luminescence and excellent reproducibility have potential applications as the photoswitches and optical memory and data storage devices.

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Photochromism-induced reversible upconversion luminescence modulation has received an extension attention due to its promising applications in anti-counterfeiting, optical storage, and switches. In this work, photochromic TiO2:Yb3+, Er3+ ceramics was prepared...

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