Silicate phosphors

A compound of formula (1),

• (Ba2−a−b−c−dMaAbREcDd)(Mg1−e−f−g−jM′eA′fRE′gC′j)(Si2−h−iB′hC″i)(O7+m−k−lXkNl) Formula (1)
• where the following applies to the symbols and indices used:
• M is Ca, Sr, Zn or a mixture of these elements;
• A is Na, K, Rb or a mixture of these elements;
• RE is La, Y, Gd or a mixture of these elements;
• D is Eu2+, Mn2+, Yb2+, Sm2+ or a mixture of these elements;
• M′ is Zr, Hf or a mixture of these elements;
• A′ is Li, Na or a mixture of these elements;
• RE′ is Sc, Lu or a mixture of these elements;
• C′ is B, Al, Ga, In or a mixture of these elements;
• B′ is Ge, Sn or a mixture of these elements;
• C″ is B, Al, Ga, In or a mixture of these elements;
• X is F, Cl or a mixture of these elements;
• N is nitrogen;
• 0≤a≤1.0;
• 0≤b≤0.6;
• 0≤c≤0.6;
• 0<d≤2;
• 0≤e≤0.3;
• 0≤f≤0.3;
• 0≤g≤0.3;
• 0≤j≤0.6;
• 0≤h≤1.0;
• 0≤i≤0.6;
• 0≤k≤2.1;
• 0≤l≤2.1;
• −2.0≤m≤2.0;
• wherein at least one and a maximum of three of the indices b, c, e, f, g, h, i, j, k, and l is ≠0;
• and
• wherein the compound contains a coating of aluminum oxide which has been deposited by an ALD process.